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3 Recommended Short-Term Recovery Strategy In this chapter, the committee presents a summary of the analysis that informed its recommended prioritiza- tion. As noted above, prior to the meeting, one or more committee members with the requisite expertise was assigned the task of preparing a detailed review of the issues associated with the descoping or demanifesting of a particular NPOESS or GOES-R measurement capability. In forming its judgments, the committee relied on the information in these presentations as well as the recommendations and detailed background information found in several recent NRC reports. The text in this chapter provides highlights of the factors that informed the committeeâs ranking; however, it is not meant to be an exhaustive summary of the information considered by the committee. RATIONALE FOR PRIORITIZATION: NPOESS LOST CAPABILITIES Microwave Radiometry Related NPOESS Sensor CMIS Post-Nunn-McCurdy âA reduced capability sensorâ Status CMIS canceled; descoped MIS instrument to be included on C2 and later platforms Climate Applications Sea-surface temperature and wind, sea ice extent, snow cover, soil wetness, atmospheric moisture Mitigation Priority Tier 1 The process by which the committee performed its prioritization is discussed in Chapter 2; the priorities are based on an average of each â memberâs numerical ranking of the importance of the lost or degraded climate capability, according to an unweighted average of responses to the nine questions shown in Chapter 2. See especially the report of the June 2007 workshop (NRC, 2008; reprinted in Appendix B) and Earth Science and Applications from Space: â National Imperatives for the Next Decade and Beyond (NRC, 2007); Ensuring the Climate Record from the NPP and NPOESS Meteorological Satellites; and Climate Data Records from Environmental Satellites: Interim Report (NRC, 2004). Some of the material in this chapter was revised and/or extended after the ranking process was completed. These changes improved the â clarity and depth of the analyses in this chapter; they did not, however, alter the committeeâs findings shown here. 29
30 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Highlights of Analysis Satellite microwave (MW) radiometry has a 35-year heritage of providing highly accurate geophysical re- trievals for Earth science. By viewing Earth over a broad spectral band ranging from 6 to 90 GHz, a large set of environmental parameters can be simultaneously estimated. The lower frequency channels penetrate the layers of cloud, giving an uninterrupted view of Earthâs surface. MW surface measurements include sea-surface temperature and wind, sea ice extent, snow cover, and soil wetness. The higher frequencies provide information on atmospheric moisture in all of its various forms: vapor, cloud, rain, and ice. The alteration of the planetâs hydrologic cycle due to global warming is one of the most (if not the most) critical issues associated with climate change, and satellite MW radiometry products are important inputs for the calculation of the planetâs changing water and energy budget. MW radiometry provides direct measurement of precipitation over both land and ocean. Over the ocean, sea-surface temperature, wind speed, and water vapor are retrieved, all of which are needed for the computation of evaporation; there is also the potential to determine water vapor advection and storage, drivers for air-sea fluxes, and global ocean circulation and upwelling. Ad- ditional hydrologic parameters are sea ice extent, snow cover, and soil wetness, although the latter two are more qualitative measurements. The importance of sea-surface temperature (SST) to climate research/science is hard to overstate. For example, SST is a key parameter in determining how the water and energy fluxes at the air-sea interface affect the hydrologic cycle and the surface radiation balance (e.g., Curry et al., 2004). The intensity, frequency, and location of hur- ricanes are in part determined by the availability of oceanic heat to sustain, encourage, or dissipate these storms. Climate oscillations such as the El NiÃ±o Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO) all have characteristic signatures that are visible in patterns of SST, precipitation, water vapor, cloud cover, and surface winds (scalar and vector). Because 6 GHz MW observations penetrate the clouds, are not affected by aerosols, and are only slightly affected by water vapor (an effect that is easily removed using higher frequency channels), the microwave radiometer has a distinct advantage over infrared sensors. The endemic cloud cover at high latitudes prevents monitoring of ocean temperatures by infrared radiometers, and microwave radiometers provide the only way to continually measure SST in these vital Arctic regions, which are now experiencing rapid climate change. Tropical convergence zones are also prime examples of persistently cloudy regions where SST detection by infrared sensors is problematic. However, the MW radiometer cannot provide the high spatial resolution or the near-coastal retrievals offered by the IR techniques. The two techniques are thus highly synergistic, and the combination of the MW radiometer with IR measurements provides the best means to accurately measure SST. Microwave radiometers, specifically the Scanning Multi-channel Microwave Radiometer (SMMR) and Special S Â ensor Microwave Imager (SSM/I), provided the first convincing evidence that the Arctic polar ice was depleting. The Arctic ice plays a critical role in global climate change by regulating ocean-atmosphere transfers of energy and water and helping control ocean surface salinity. Sea ice albedo feedbacks amplify climate impacts in the polar regions. Variables such as ice extent, concentration, and type are important for navigation as well as for marine habitat assessment. Satellite observations of September minimum sea ice show that sea ice extent has declined 8.6 percent +/â 2.9 percent per decade over the period 1979-2006 (Serreze et al., 2007). Snow cover in the North- ern Hemisphere has also declined by 1.28 Ã 106 km2 over the period 1972-2006 (DÃ©ry and Brown, 2007). This decline in snow cover is significant because, compared with other land cover types, snow has a very high albedo and climate feedbacks are felt on local, regional, and even hemispheric scales. Monitoring water vapor via its emission at 22.235 GHz, the MW radiometer provides the most accurate means to measure total columnar â water vapor. In the absence of rain, the MW radiometer also provides the most accurate means to measure total columnar cloud water. By design (i.e., by including the 89 GHz channels), the MW radiometer can detect scattering from ice particles, the third phase of water. However, unlike the measurements of water vapor and liquid water, this detection is not a quantitative measurement. In the IPCC 4th Assessment it is stated that âcontinuous satellite measurements capture most of the Earthâs seasonal snow cover on land, â and reveal that Northern Hemisphere spring snow cover has declined by about 2 percent per decade since 1966, although there is little change in autumn or early winter. In many places, the spring decrease has occurred despite increases in precipitationâ (IPCC, 2007, p. 18). Recent unpublished work concludes that snow cover in the Northern Hemisphere has been declining at a rate of about 3 to 5 percent per decade Âduring spring and summer (Brodzik et al., 2006).
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 31 As has been demonstrated via WindSat, microwave radiometers are capable of measuring vector winds (that is, both wind direction and speed) over the ocean by using polarimetric observations. Surface vector wind (SVW) controls the air-sea transfer of momentum and vorticity, and the surface wind speed modulates air-sea transfers of heat and fresh water. SVW and wind stress curl drive coastal and open-ocean upwelling processes affecting global primary production and oceanic mass transfers (e.g., cross-shelf transport and CO 2 uptake). As such, characteriza- tion and quantification of the role of the global ocean as a planetary heat and carbon sink depend critically on ac- curate representation of the global SVW. However, passive MW measurements of vector winds are not comparable in accuracy, coverage, or resolution to measurements from radar scatterometers such as the Sea Winds instrument on NASAâs QuikSCAT. The differences are even more dramatic when comparing the capabilities of passive ra- diometers (e.g., WindSat and CMIS/MIS) with those of the advanced ocean vector winds scatterometer mission, known as the Extended Ocean Vector Winds Mission (XOVWM), which was recommended in the 2007 NRC Earth Science and Applications from Space decadal survey. XOVWMâs ability to provide highly accurate wind vectors at a high spatial resolution (5 km) in the presence of rain and near coastlines (target value of 2.5Â km) far exceeds what is achievable by passive radiometry. Thus, provision of climate quality ocean vector winds measurements requires consideration of mitigation options beyond the NPOESS passive microwave sounder. Scatterometers are active spaceborne systems that emit directed microwave signals and detect correspond- ing backscatter to infer surface wind speed and direction over water surfaces. SVW retrievals from scatterometer observaÂtions have been used to demonstrate global surface wind kinetic energy content, vorticity, and divergence at spatial scales of about 25 km. SVW from scatterometer observations have a pronounced impact on the response of global ocean general circulation models (OGCMs) in terms of, for example, mass and heat transports, overturning circulations, and synoptic eddy field energy (Milliff et al., 1999). The spatial resolution and global coverage of SVW from scatterometer observations are commensurate with, and provide forcing for, the ocean synoptic-scale eddies (e.g., Spall, 2007) that transport heat, organize and sequester ocean ecosystems, and contribute significantly to the ocean general circulation (Hughes and Wilson, 2008). OGCMs are a critical component of the coupled climate model systems from which climate scenario calculations are obtained. The ocean role in climate scenarios gleaned from the coupled systems must be verified against ocean-only OGCM calculations driven by realistic SVWs. The radar backscatter signal detected by scatterometers has other important climate implications as well. For example, reprocessing of the 1999 to 2005 QuikSCAT backscatter time series for sea ice classification produced a unique record that captured the diminishing Arctic multiyear and summer sea ice extent conditions leading to a record minimum in 2005. Drastic regional reduction and redistributions of the perennial ice in 2005 resulted in a net decrease in the total perennial ice extent of an area equivalent to the size of Texas (Nghiem et al., 2006). The Conical-scanning Microwave Imager and Sounder (CMIS) instrument that was planned for NPOESS C1 and subsequent platforms was canceled as a result of the Nunn-McCurdy certification. A descoped sensor, desig- nated as MIS (Microwave Imager and Sounder), is now planned to replace CMIS on NPOESS C2 and subsequent platforms. At its December 2007 meeting, the committee heard briefings by NPOESS officials on the status of the MIS procurement. At that time, formal specifications for MIS could not be disclosed; however, the committee was informed that the instrument would include core radiometry channels (10-89 GHz), soil moisture/sea surface temperature channels (6 GHz), and wind direction (10-37 GHz) polarimetric channels, while relying upon CrIS/ ATMS to meet temperature and moisture sounding requirements that have been designated as key performance â WindSat is a joint IPO/DOD/NASA risk reduction demonstration project intended to measure ocean surface wind speed and wind direction from space using a polarimetric radiometer. Launched in June 2003 by an Air Force Titan II rocket into an 830 km 98.7 degree orbit, it has exceeded its 3-year design life. See http://www.nrl.navy.mil/WindSat/index.php. The decadal survey recommendation for XOVWM was prompted in part by the recognition of the importance of data from scatterometers to climate research and prediction.â See also Z. Jelenak, P.S. Chang, J. Sienkiewicz, R. Knabb (NOAA), and D. Chelton (Oregon State Uni- versity), âCurrent and Future Needs and Solutions for Ocean Surface Vector Wind Measurements from Space,â presentation to the committee, June 20, 2007, available at www7.nationalacademies.org/ssb/NPOESSWorkshop_NRC_Workshop_June07_zjelenak.pdf; Freilich and ÂVanhoff (2006), and Monaldo (2006). Also of interest regarding XOVWM versus QuikSCAT and WindSat are presentations given at the NOAA OperaÂtional Satellite SVW Winds Requirements Workshop on June 5-7, 2006; available at http://manati.orbit.nesdis.noaa.gov/SVW_nextgen/Â workshop_Âoutline.html.
32 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT BOX 3.1 SUAG Priorities 1.â Core Radiometry Channels (10-89 GHz) 2.â Sounding Channels (50-60, 166 and 183 GHz) 3.â Soil Moisture/Sea Surface Temperature (6 GHz) 4.â ind Direction (10-37 GHz polarimetric channels) W 5.â Upper Atmospheric Sounding (60-63 GHz) SOURCE: Presentation to the committee, October 9, 2007. Available at http://www7.nationalacademies.org/ssb/ NPOESS_mitigate_descope_presentation_Schneider_StGermain.pdf. parameters (KPPs). This would be a deviation from the NPOESS Science User Advisory Group (SUAG) recom- mendations (see Box 3.1), which placed a clear emphasis on atmospheric temperature and moisture vertical profiles over polarimetric channels (SUAG priority 4). However, shortly before this report went to press, the committee learned that the first MIS, scheduled for launch on NPOESS C2, will, in fact, be procured with the desired sound- ing channels (SUAG priority 2). The first MIS is planned for the C2 platform, which is currently scheduled for launch no earlier than 2016. For a variety of reasons, the committee believes future planning should include the significant likelihood for another slip in the schedule past 2016. Thus, the committee sees a very real risk of a substantial gap in the time series of microwave climate products. Currently, there are only two operational MW radiometers that have the spectral bands and spatial resolution necessary for adequate climate monitoring: AMSR-E on Aqua and WindSat on Coriolis. 10 Unfortunately, both of the sensors are already beyond their specified mission life, and it is extremely unlikely that either sensor will be in operation when the C2 platform is launched. A follow-on, AMSR-2, is scheduled to fly on JAXAâs GCOM-W platform, but not before 2012, and no fol- low-on is planned for WindSat. Furthermore, the GCOM-W launch schedule may slip, and premature spacecraft failures have occurred in the previous two JAXA Earth observation missions. In view of this, relying solely on AMSR-2 to continue the MW climate time series carries considerable risk. Another MW radiometer, GMI, 11 is scheduled for launch in 2013, but it does not have 6 GHz channels or the high spatial resolution of AMSR and WindSat. In addition, GMI will not view the high latitudes due to its 65Â° inclination orbit. The only other U.S. MW radiometers (other than sounders) that are scheduled for launch are part of the SSM/IS series. However, the SSM/IS lacks both the spatial resolution and spectral range required for adequate climate monitoring. Should AMSR-2 be delayed or experience an early failure, a significant data gap of many years will occur. In the committeeâs view, this would be devastating to climate monitoring of SST and the hydrologic cycle. Given the Âimportance of the MW radiometer for climate monitoring, the committee found cancellation of CMIS on the The DOD and DOC would consider the NPOESS system to have a major flaw if it did not meet its key performance parameters (KPPs) as â outlined in the Integrated Operational Requirements Document (IORD) II (December 10, 2001). A KPP is defined as a measurable capability or characteristic a system must deliver or display when declared operational. Any system or program not meeting a KPP is a candidate for termination. See âThe Future of NPOESS: Results of the Nunn-McCurdy Review of NOAAâs Weather Satellite Program,â Hearing before the Committee on Science, House of Representatives, One Hundred Ninth Congress, Second Session, June 8, 2006, available at http://bulk. resource.org/gpo.gov/hearings/109h/27970.pdf. The SUAG represents the primary U.S. government users of NPOESS data. See Memorandum of Agreement Between the Department of â Commerce, Department of Defense, and National Aeronautics and Space Administration for the National Polar-Orbiting Operational Environ- mental Satellite System (NPOESS). Available at http://www.hq.nasa.gov/pao/History/presrep95/f1.htm. 10 Both of these sensors have the C-band channels (i.e., 6 GHz) necessary for global SST and surface wetness retrievals and a large enough antenna (i.e., 2 m) to provide adequate spatial resolution. 11â The GPM Microwave Imager (GMI) is NASAâs key contribution to the U.S.-Japanese Global Precipitation Mission, which is scheduled for launch in 2013.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 33 NPOESS C1 platform both puzzling and ill advised. CMIS represented the state of the art in satellite MW Âradiometers and was intended to continue, with a higher degree of accuracy and resolution, the time series of many fundamental climate variables. The ability of CMIS to measure surface characteristics through clouds and provide direct measureÂ ments of the changing hydrologic cycle made it a unique and essential sensor for climate. In the committeeâs view, the cancellation of CMIS and the decision to forgo the inclusion of its replacement, MIS, on NPOESS C1, jeopardizes a national commitment to the enhancement of scientific understanding of global climate change. 12 Finding:â In view of its capability for monitoring the hydrologic cycle, SST, and sea ice, the committee ranks provision of microwave radiometry as its highest priority. The committee finds that AMSR-2 by itself is not sufficient to avoid a data gap and recommends that a mitigation strategy be formulated to supplement AMSR-2 with another MW radiometer of similar design. This ranking stems largely from it receiving the highest score for its use in climate data records (question 1), role in reducing uncertainty (question 2), use in re- analysis (question 4), contributions to understanding the climate system (question 8), and use in other disciplines (question 9). Preferred Recovery Strategy and Other Mitigation Options The preferred mitigation is to build a new MW radiometer specifically designed for climate monitoring, and fly it on either a free flyer or a flight of opportunity. Formation flight with NPP or NPOESS C1 is highly desir- able, as it would enable provision of near-simultaneous IR measurements from CrIS/ATMS to complement the MW observations. The radiometer could be considerably simpler than MIS in that it does not need to have the polarimetric channels required for recovery of vector winds, nor the sounding channels; a basic AMSR-type design would be sufficient. Additional mitigation options include: â¢ Adding C-band channels to NASAâs GMI instrument, and enlarging its antenna. 13 Although GMIâs orbit inclination of 65Â° is not ideal for ocean monitoring, it is sufficient to view most ocean areas. â¢ Modifying the MW radiometer that is planned for the advanced scatterometer mission XOVWM, which has a recommended launch date of around 2012, to include at least 3 or 4 frequencies, one being C-band, as well as an improved on-board calibration system. The synergy of a scatterometer and a MW radiometer on the same platform is significant and would improve both the scatterometer and radiometer retrievals. There are significant costs and schedule impacts associated with each of these options. Accordingly, the committee makes the following recommendations: 1. NASA and NOAA should initiate a study as soon as practicable to address continuity of microwave radiometry and to determine a cost-effective approach to supplement the AMSR-2, carried on the Japanese spacecraft GCOM-W, with another microwave radiometer of similar design. The agencies should also con- sider the feasibility of manifesting a microwave radiometer on a flight of opportunity or free flyer to cover the microwave radiometry gap anticipated with a delay in accommodation of MIS until NPOESS C2. 2. The agencies should provide funding for U.S. participation in an AMSR-2 science team to take full advantage of this upcoming microwave radiometer mission. 3. The NPOESS Integrated Program Office should continue with its plans to restore a microwave sounder to NPOESS C2 and subsequent platforms, with an emphasis on SUAG priorities 1 through 3 (core radiometry, sounding channels, and soil moisture/sea surface temperature). U.S. Climate Change Science Program, âStrategic Plan for the Climate Change Science Program,â available at http://www.climatescience. 12â gov/. Without the C-band channels, accurate SST measurements cannot be obtained for SST less than 12Â°C. This excludes a large portion of 13â the worldâs oceans.
34 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Scatterometry is the clearly preferred approach for obtaining ocean vector winds, and the committee urges the agencies to hasten development of operational ocean vector wind capability to meet both climate and weather fore- casting needs.â Considering the advanced capabilities of XOVWM as compared to the QuikSCAT-type scatterom- eter (particularly with respect to measurement in storms and hurricanes), the preferred option is to put XOVWM on the fast track and launch as soon as possible, as opposed to launching another QuikSCAT. Due to fundamental limitations of the passive MW approach for measuring vector winds, the committee does not view restoration of polarimetry to MIS as adequate to meet the data needs of climate researchers studying connections between sea- surface vector winds and climate. Accordingly, the committee offers the following recommendation: 4. NASA and NOAA should devise and implement a long-term strategy to provide sea-surface wind vector measurements. The committee finds important limitations in the planned reliance on a Âpolarimetric radiometer for this measurement; instead, the preferred strategy is timely development and launch of the next-generation advanced scatterometer mission, that is, the Extended Ocean Vector Winds Mission (XOVWM) recommended in the 2007 NRC decadal survey Earth Science and Applications from Space. Radar Altimetry Related NPOESS Sensor ALT Post-Nunn-McCurdy Status âA demanifested sensorâ Climate Applications Sea level height, regional ocean currents, basin-scale ocean circulation Mitigation Priority Tier 1 Highlights of Analysis Sea level is a fundamental indicator of changes in Earthâs climate. Sea level measurements provide insight into ENSO processes (e.g., onset, strength, planetary waves) and other climate oscillations (e.g., PDO) that are important for understanding the impacts of short-term variations in climate, and are key to observing changes in ocean circulation. Sea level changes, in response to heat absorption by the oceans (via thermal expansion) as well as the contribution of melting ice from glaciers and the polar ice caps, will have profound socioeconomic impacts on coastal populations around the world. Thus, sea level is a critically important variable to monitor as Earth warms; it is needed to both predict future impacts and inform mitigation strategies. Prior to the satellite era, tide gauge measurements were the primary means of monitoring sea level change. However, their poor spatial distribution and ambiguous nature (e.g., vertical land motion can cause erroneous signals that mimic the effects of climate change at some sites) made them of limited use for climate studies. With the launch of TOPEX/Poseidon (T/P) in 1992, satellite altimeter measurements with sufficient accuracy to monitor sea level change became available (Cazenave and Nerem, 2004). TOPEX/Poseidon was the first mission with sufficient measurement accuracy (corrections for ionosphere and troposphere delays), orbit accuracy (three separate precision orbit determination systems), and orbit sampling characteristics (orbit does not alias tidal varia- tions to âclimate-likeâ frequencies) that monitoring small (mm/year) changes in sea level was possible. 14 Jason-1, launched at the end of 2001, has continued the T/P measurements in the same orbit/ground track, including a critical 6-month intercalibration phase with T/P.15 The TOPEX/Poseidon and Jason-1 missions have resulted in a continuous 15-year time series of precisely calibrated sea level measurements (Figure 3.1). These measurements have allowed satellite monitoring of global mean sea level change (Figure 3.2), which has risen at an average rate of ~3.5 mm/year during the altimeter era (Figure 3.3), nearly double the rate observed by tide gauges over the While other satellite altimeter measurements had previously flown, they either did not have the instrument or orbit determination precision 14â (Seasat, Geosat), and/or they flew in Sun-synchronous orbits (e.g., ERS, Envisat) that are undesirable for climate research and applications. Overlap between the missions is critical for assessing instrument performance, differences between instruments, and other factors that 15â vary from one mission to the next.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 35 60 50 40 30 20 10 0 -10 1993 1995 1997 1999 2002 2004 2006 2008 FIGURE 3.1â Global mean sea level variations (mm) from the TOPEX/Poseidon and Jason-1 missions. SOURCE: Courtesy of Centre National dâEtudes Spatiales/D. Ducros. last century (Leuliette et al., 2004; Beckley et al., 2007). Another powerful aspect of satellite altimetry is that it provides maps of the spatial variability of the sea level rise signal, which is valuable for the identification of sea level âfingerprintsâ associated with climate change (Mitrovica et al., 2001). Jason-2, also called the Ocean Surface Topography Mission (OSTM)/Jason-2, carrying similar payload to Jason-1 with improved technology, is scheduled for launch in June 2008,16 and will hopefully enjoy a similar intercalibration period with Jason-1. Discussions for a Jason-3 mission are currently under way between NOAA and EUMETSAT as part of a transition of satellite altimetry to âoperationalâ status, but the mission is still very uncertain, and a gap after Jason-2 is a very real possibility. Researchers hope to avoid a gap in this 15-year satellite record as measurements from tide gauges and Sun-synchronous satellite measurements would not be sufficient to accurately determine the bias between the two time series on either side of the gap. A measurement gap presents two problems: (1) scientists are unable to monitor sea level changes due to sudden shifts in the climate system or natural events (e.g., ENSO events, volcanic eruptions, etc.) occurring during the gap, and (2) a gap in the record will make it more difficult to determine if the rate of sea level rise is acceleratingâultimately requiring an even longer time series before this determination can be made. Sea level measurements from satellite altimetry benefit a broad array of climate science disciplines includ- ing ocean science, cryospheric science, hydrology, and climate modeling applications because sea level change is a barometer for changes in the global water cycle. While measurements from satellite gravity missions such as GRACE provide direct measurement of hydrologic and cryospheric contributions to sea level change, satellite altimeter measurements measure the total sea level change, including ocean thermal expansion not observed by GRACE, and thus are best suited for measuring the spatial variability of the sea level change and predicting the 16 â ote added in proof: The present report was completed before the successful launch of OSTM/Jason-2 on June 20, 2008. N
36 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Figure 3.2a.eps FIGURE 3.2â Sea level (from Jason-1 and TOPEX/Poseidon) in the Pacific averaged over 5Â°S-5Â°N, 210Â°-270Â°E (bottom) and as a change map (Jason-1 data only, top). SOURCE: Courtesy of L. Fu/NASA/JPL. figure 3.2b.eps fixed image, probably landscape socioeconomic impacts on coastal areas. Sea level measurements were used prominently in the most recent IPCC assessment, and promise to be an even more integral part of future assessments because of their direct relation to changes in ocean heat content and land ice melt, as well as their use in assessing global climate models through hindcasts (Rahmstorf et al., 2007). The predictions of future sea level change were one of the most contentious aspects of the IPCC 4th assessment and thus satellite altimetry will be an important tool for scientists preparing future assessments. Sea level measurements are also used extensively in ocean reanalysis efforts (e.g., ECCO, SODA) and short- term climate predictions.17 However, sea level measurements have not been extensively used in long-term climate ECCO is the acronym for Estimating the Circulation and Climate of the Ocean; SODA is the acronym for Simple Ocean Data 17â Assimilation.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 37 IB correction applied Univ of Colorado 2008_rel1 -15 -12 -9 -6 -3 0 3 6 9 12 15 mm/yr FIGURE 3.3â Trends (mm/year) in sea level change over 1993-2007 from TOPEX/Poseidon and Jason-1 altimeter measure- ments. SOURCE: Courtesy of Colorado Center for Astrodynamics Research, University of Colorado at Boulder. For more infor- mation, see http:// sealevel.colorado.edu and Leuliette, E.W., R.S. Nerem, and G.T. Mitchum, Calibration of TOPEX/Poseidon and Jason altimeter data to construct a continuous record of mean sea level change, Marine Geodesy 27(1-2):79-94, 2004. figure 3.3.eps projections because the current and future response of the ice sheets is poorly understood. Nevertheless, sea level measurements are an important tool for testing climate model projections. The committee notes that satellite altimetry is a very mature measurement technique. While there is still active research on improvements in the measurement processing, especially for the demanding applications of climate science, the measurement system as a whole is very well understood. The ALT instrument, demanifested from NPOESS following Nunn-McCurdy certification, is a mature state-of-the-art sea level measurement system with a well-understood long-term calibration scheme (tide gauges). However, the NPOESS Sun-synchronous orbit is incompatible with climate science needs for precision radar altimetry. Satellite altimetry also requires precision orbit determination, which is accomplished via dedicated precision satellite geodetic observations (e.g., GPS, DORIS, SLR). However, the precision of these techniques can be compromised as a result of their placement on large satellites that have multiple instruments and a variety of accommodation requirements. For these reasons, the originally intended NPOESS altimetry capability was undesirable for climate studies. In summary, the committee recognizes the importance of an uninterrupted record of sea level change mea- surements for climate science research and policy making, and thus strongly advocates that the record of sea level change from these missions be continued. However, the originally intended NPOESS altimetry capability was ill- suited for climate studies, primarily because the NPOESS Sun-synchronous orbit was problematic for separating tidally driven versus climate-related sea level changes. Thus, restoration of the ALT sensor to NPOESS would require justification via applications outside climate science.
38 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Finding:â Overall, radar altimetry ranks in the first tier of climate priorities. Radar altimetry ranked highly in terms of contribution to climate data records (question 1), its role in climate prediction (question 3), measurement maturity (question 5), uniqueness (question 6), and use in reanalysis (question 7). Preferred Recovery Strategy and Other Mitigation Options The committeeâs preferred recovery strategy for radar altimetry climate needs is to fly a Jason-3 mission and subsequent series of precision altimetry free flyers in order to continue the climate data record that was initiated by TOPEX/Poseidon and Jason-1, and is to be continued in the near term by OSTM/Jason-2. While flying Jason-3 in the same orbit (66Â° inclination, 1,336 km altitude) as the earlier satellites is preferable, proposals to increase the inclination (improving the latitudinal coverage) and lower the altitude (reducing spacecraft cost) are acceptable, particularly if there is overlap with Jason-2 (allowing the intercalibration of the measurements from the two orbits) and if tidal aliasing is properly considered in the orbit selection. Changes to the near 10-day repeat period of the current orbit are not a major concern for climate studies. The committee is also aware of efforts to develop a âwide-swathâ altimeter mission for hydrologic and oceanic applications recommended for launch in the 2013-2016 time frame by the decadal survey. While the committee supports this initiative, the utility of this novel measurement approach for sustained climate monitoring will not be fully known until the measurements have been collected and analyzed, and thus it is not considered a substitute for a Jason-3 mission. There are no apparent viable options should a Jason-3 mission fail to materialize.â While other altimeter mis- sions are planned in the European community, they employ Sun-synchronous orbits that are not suitable for climate studies. Proposed alternatives to Jason-3 must properly consider requirements for orbit selection, measurement accuracy, calibration, and precision orbit determination, while relying upon mature, low-risk technology. Recommendation:â A precision altimetry follow-on mission to OSTM/Jason-2 (i.e., Jason-3) should be devel- oped and launched in a time frame to ensure the necessary mission overlap. The agenciesâ long-term plan should include a series of precision altimetry free flyers in non-Sun-synchronous orbit designed to provide for climate-quality measurements of sea level. Earth Radiation Budget Related NPOESS Sensor ERBS Post-Nunn-McCurdy Status âA demanifested sensorâ Climate Applications Earth radiation budget at the top and bottom of the atmosphere Mitigation Priority Tier 1 Highlights of Analysis Measurements of regional and global radiation balance date to the 1960s when the first satellites were launched, and they were further enabled with the launch in the late 1970s of Nimbus 6 and 7, which carried the first true broadband radiation scanning sensors. NASAâs Earth Radiation Budget Experiment provided the second genera- tion of true broadband data and the first scanners with sufficient spatial resolution to separate clear-sky scenes and allow for the direct observation of cloud radiative effect (Figure 3.4). The third-generation instrument, CERES (Clouds and the Earthâs Radiant Energy System), is included on the TRMM (1997-), Terra (1999-), and Aqua (2002-) missions. Calibration and data analysis accuracy have improved with each generation. Earth radiation budget products currently include both solar-reflected and Earth-emitted radiation from the top of the atmosphere (TOA) to Earthâs surface. Through synergies with simultaneous measurements by other EOS instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS), it is possible to relate cloud
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 39 (a) (b) figure 3.4a.eps original ia a .jpg photograph FIGURE 3.4â (a) Installation of flight multilayer insulation on CERES Flight Models 1 and 2 at the TRW clean room facility after completion of calibration in preparation for shipment to Vandenberg for integration on Terra. SOURCE: Courtesy of NASA, available at http://asd-www.larc.nasa.gov/ceres/terra/pics.html. (b) Terra/CERES View of Earth. SOURCE: Courtesy figure 3.4b.eps, originally a .tif file of NASA/Goddard Space Flight Center Scientific Visualization Studio, available at http://visibleearth.nasa.gov/view_rec. php?id=11907.
40 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT properties to the radiation budget and determine both climate forcing and climate response. Analyses of CERES data are leading to a better understanding of the role of clouds and the energy cycle in global climate change, and to improved assessments of the change in Earthâs climate as a function of time. Unscrambling climate signal cause-and-effect requires a complete parameter set at climate accuracy. Earth radiation budget measurement utilization requires multispectral imagery data, which are currently supplied by MODIS; in the NPOESS time frame, these data will be supplied by VIIRS. CERES analyses routinely merge TOA radiation data with cloud, aerosol, snow, and ice property retrievals from MODIS, microwave sea-ice coverage, aerosol assimilation data, 4-D assimilation of weather data, and 3-hour geostationary satellite data. The largest uncertainty in global climate sensitivity over the next century is cloud feedback (especially for low clouds). IPCC coupled atmosphere-ocean models show that cloud feedback is linearly related to top-of-atmosphere net cloud radiative effect, and climate sensitivity is linearly related to cloud feedback (Soden and Held, 2006). CERES will observe decadal changes in net cloud radiative effect that will reduce the uncertainty in cloud feed- back and therefore climate sensitivity. To achieve this objective, the minimum calibration goal for decadal change observations of TOA radiation is 0.35 percent per decade for SW and 0.6 percent per decade for LW (95 percent confidence). These goals cannot be achieved if there is a gap in the TOA radiation record, as they are a factor of 5 more stringent than the current state of the art for absolute accuracy in broadband radiometers in the SW, and a factor of 2 more stringent in the LW. Thus, TOA radiation measurements must be overlapping from one mission to the next; a gap of any length will restart the climate record at zero. Earth radiation budget measurements have played an important role in climate prediction and projections. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4) 18 model results of the change in global mean surface air temperature and cloud radiative effect (CRE) under the A1b emission scenario suggest that monitoring the future evolution of CRE gives an earlier indication of what climate sensitivity trajectory we are on than does monitoring of the global mean temperature (Figure 3.5). For example, by 2050 an observational record of CRE with a stability of 0.5 Wmâ2 per 50 years would eliminate approximately 50 percent of the models as being inconsistent with the observed record. Therefore, based on these results, Global Circulation Models (GCMs) suggest that ERB measurements likely provide a better metric than surface air temperature for predicting the actual climate sensitivity trajectory. Broadband radiation budget data for ERBS and CERES were used in the most recent IPCC 2007 observations chapter to determine the interannual variability in ocean heat storage (global net radiation, e.g., Wong et al., 2006), to counter spurious climate signals in global planetary albedo such as those from the astronomical Earthshine observations (Wielicki et al., 2005), and to put in global energy perspective inferences of âglobal dimmingâ from surface broadband radiometers. The ERBS data also provided observations of decadal variations of tropical SW, LW, and net fluxes. More recently, CERES data were used to investigate a 2006 claim of ocean cooling from recent Argo data. This erroneous claim resulted from in situ biases between the old Expendable Bathythermograph (XBT) and new Argo in situ data (Willis et al., 2007). CERES data are also being used as the most accurate reference data for the WCRP GEWEX Radiative Flux Assessment, an international effort under way by over 50 international researchers evaluating both surface and TOA fluxes, their accuracy, and their ability to resolve decadal change in the climate system. Finding:â Sustaining the Earth radiation budget climate measurement record into the future ranked in the first tier of climate priorities. The Earth radiation budget measurement record ranked higher in the area of measurement maturity (question 5) than any other climate capability considered by the committee. It also ranked among the highest (second or third place) in the areas of extent the data are used in monitoring and providing a historical record of the global climate, extent this measurement is important in reducing âuncertainty,â extent the data are used by the IPCC and the CCSP, and the measurementâs role in contributing to an overall improved understanding of the climate system (questions 1, 2, 7, and 8). The three Working Groupsâ full reports and the Synthesis Report, the final part of the Fourth Assessment Report (AR4), are available 18â online at http://www.ipcc.ch.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 41 (a) (b) fig 3.5a.eps fixed image FIGURE 3.5 Change in global (a) surface air temperature and (b) cloud radiative forcing between 2000 and 2080 for IPCC AR4 GCM simulations (5-year running means). SOURCE: Courtesy of B. Soden, NOAA. figure 3.5b,.eps fixed image
42 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Preferred Recovery Strategy and Other Mitigation Options The preferred recovery strategy is consistent with the recommendations of the decadal survey and June 2007 workshop report. Specifically, the agencies should (1) fly the CERES FM-5 on NPP, even if it causes a modest delay to the NPP launch date,19 and (2) develop an Earth radiation budget instrument (series) to follow CERES FM-5 to fly in at least one Sun-synchronous orbit and continue and extend the rich Earth radiation budget long- term measurement record.20 Due to ancillary data requirements, the CERES or ERBS-like instrument should either fly on the same platform as a VIIRS (or equivalent) imager or in formation (within 3 to 6 minutes) with the NPOESS VIIRS imager in the 1:30 LT orbit. The decadal surveyâs Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission could fundamentally change this dynamic, but it now appears unlikely to launch before 2013. CLARREOâs nadir track spectrometer will acquire data traceable to SI (Systeme Internationale) standards across the full solar and IR broadband spectra at decadal change accuracy; these data could then be used to provide calibration transfer across short gaps in the CERES broadband record (NRC, 2007, pp. 93-95). CERES-like full-swath broadband data will still be required for space/time sampling of global change, but short gaps in the measurement record could then be of less consequence. Recommendation:â To minimize the risk of a potential data gap, the committee reiterates the recommenda- tion of the 2007 Earth Science and Applications from Space decadal survey to manifest the CERES FM-5 on NPP.21 The agencies should further develop an ERB instrument series and provide for subsequent flights on Sun-synchronous platforms to continue the Earth radiation budget long-term record. Hyperspectral Diurnal Coverage Related NPOESS Sensor CrIS/ATMS Post-Nunn-McCurdy Status âA reduced coverage sensorâ Climate Applications Vertical temperature and moisture profiles, outgoing longwave radiation, greenhouse gas amounts, cloud properties, precipitation Mitigation Priority Tier 2 Highlights of Analysis Understanding the diurnal variation of climate-relevant parameters and processes is essential for the improve- ment of the underlying physics of climate models, which must sufficiently capture the physics of short-time-scale processes to enable accurate predictions over long time periods.22 Greater sampling of the diurnal variability of 19â The committee was informed NPP could launch no earlier than 14 months after delivery of the final instrument. As this report was being prepared, NOAA announced a delay in delivery of the VIIRS instrument to NPP (now anticipated for 1Q09) which would cause a launch delay. Restoration of CERES FM-5 to NPP should not require further launch delay. The committee was informed that there are sufficient spare parts to assemble a CERES FM-6 for flight on C1, which might be leveraged 20â as a potential cost savings option. This view was also expressed by many of the participants at the June 2007 workshop; it is also endorsed in the ongoing NASA-NOAA 21â study. See Appendix B. Undersampled diurnal variability introduces a bias into the time-mean behavior derived from observations, impacting the degree to which 22â the global structure and evolution of a climate-relevant property can be reconstructed, particularly for the small-scale behaviors inherent to distributions of water vapor and cloud cover (Salby and Callaghan, 1997). Diurnal variations cannot be determined from a single polar-orbiting platform, as diurnal variability is indistinguishable from the time-mean. However, systematic error can be reduced by the use of measurements from multiple platforms in polar orbit, or through the improved temporal coverage obtained in geostationary orbit. The change of diurnal cycle of the surface air temperature implies the existence of a substantial climate forcing located in continental â r Â egions. Karl et al. (1993) indicated that diurnal cycle changes non-symmetrically: averaged minimum temperature over 50 percent of Northern
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 43 0.3 All Spring 0.2 Summer Difference from daily average (oC) Autumn Winter Average T and T+12 (oC) Model 0.1 0.0 â0.1 â0.2 0 5 10 15 20 Local Hour, T FIGURE 3.6â Diurnal cycle of sea surface temperature. SOURCE: J.J. Kennedy, P. Brohan, and S.F.B. Tett, A global climatol- ogy of the diurnal variations in sea-surface temperature and implications for MSU temperature trends, Geophys. Res. Lett. 34: L05712, doi:10.1029/2006GL028920. Copyright 2007 American Geophysical Union. figure 3.6.eps vector image key parameters for climate-relevant processes (e.g., clouds, surface temperature, sea surface temperature, and humidity) will allow for improved simulation of important climate processes. Improved diurnal coverage is also needed to accurately interpret long-term climate trends. For example, changes in global sea surface temperature due to warming trends are on the order of 0.1 K per decade (Wentz and Schabel, 2004). Seasonal as well as diurnal variability must be removed from these trends in order to make an accurate observation of the warming trends. Long-term observations allow for seasonal variability to be ac- commodated;23 however, since all of these sounders are in a well-maintained Sun-synchronous polar orbit, each satellite only samples the diurnal cycle at two points. Any changes in the diurnal cycle can complicate the detection of small warming trends over time (Anderson et al., 2004). Figure 3.6 shows the diurnal cycle for SST, overlaid with the location of the AIRS, IASI, and CrIS observation locations (Kennedy et al., 2007). Quantification of the increased uncertainty introduced by the loss of CrIS in the NPOESS 05:30 terminator orbit has not been performed; however, as indicated by the figure, this time is well suited to fitting the diurnal cycle and significantly reducing Hemisphere land in 1951-1990 increased by 0.85Â°C, while average maximum temperature increased only by 0.28Â°C. Observed variations of diurnal cycle allow the inference of fundamental information on the nature and location of main climate forcings (Hansen et al., 1995). The diurnal cycle of liquid water and cloud cover must also be included in the Earthâs radiative budget (Bergman and Salby, 1997). Diurnal cycle amplitudes are a considerable fraction of the mean (15-35 percent), especially for low clouds, and vary geographically (Wood et al., 2002). Seasonal fluctuations can be accommodated by the sounders through long-term observations. AIRS (aboard NASAâs Aqua spacecraft) 23â has thus far achieved over 5 years of observations, and IASI (aboard MetOp) is entering its second year. The NPOESS CrIS is planned to be operational for the next two decades.
44 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT uncertainty associated with its potential changes over time. The 05:30 orbit is particularly interesting, as it occurs at a transition point in the diurnal cycle from nighttime to daytime that may in some locations be highly sensitive to climate variability. Prior to the NPOESS and GOES-R descopes, unprecedented diurnal hyperspectral coverage was anticipated from CrIS (on NPOESS) and HES (on GOES-R); however, after both programs were descoped, the anticipated improvements were essentially lost. Restoring CrIS/ATMS to the NPOESS C2 and C4 platforms would allow for soundings at approximately 4-hour intervals over the United States and coastal waters for severe weather applica- tions rather than the up to 8-hour gap currently associated with the post-Nunn-McCurdy NPOESS architecture. 24 In addition to the climate value of additional hyperspectral diurnal coverage, there is an important risk mitiga- tion aspect associated with restoration of CrIS/ATMS to the C2 and C4 platforms. Current MIS specifications imply reliance upon CrIS/ATMS to meet temperature and moisture sounding KPP requirements. However, CrIS/ATMS is not currently manifested on C2 or C4; therefore, soundings will not be provided in the 05:30 orbit. Pre-Nunn- McCurdy certification, KPP redundancy was assured, as VIIRS, CrIS, and ATMS were in both the 05:30 and 13:30 orbits, with VIIRS and MetOp (carrying AVHRR, IASI, and AMSU) in the 09:30 orbit. In such a configura- tion, single points of failure in any portion of the system still allowed for KPPs to be met. Post-Nunn-McCurdy c Â ertification, however, plans for an NPOESS with VIIRS in the 09:30 orbit were terminated and CrIS and ATMS were removed from the NPOESS satellite in the 05:30 orbit, thus negating redundancy for KPPs while at the same time placing the NPOESS system in jeopardy of loss in continuity of services. An unsuccessful launch of C1, or the premature failure within the C1 sounder system, would result in unmet KPPs. 25 Finding:â Hyperspectral diurnal coverage ranked in the second tier of climate priorities for recovery. It scored highly in terms of contribution to a climate record (question 1) and measurement maturity (question 5). Preferred Recovery Strategy and Other Mitigation Options The preferred recovery strategy is to remanifest CrIS/ATMS on the NPOESS C2 and C4 platforms; thus, all NPOESS spacecraft would have as a minimum instrument configuration a VIIRS, a CrIS, and an ATMS. R Â emanifesting the sounder system on the C2 and C4 platforms would increase hyperspectral diurnal coverage to improve climate process understanding and reduce the risk of gaps in continuity of services by allowing C2 or C4 to be launched into the afternoon orbit if necessary to replace a C1 or C3 satellite. An ancillary benefit is the valuable additional data that would be available to support weather forecasting. Recommendation:â The CrIS/ATMS instrument suite should be restored to the 05:30 NPOESS orbit to pro- vide improved hyperspectral diurnal coverage and support atmospheric moisture and temperature vertical profile key performance parameters. Solar Irradiance Related NPOESS Sensor TSIS Post-Nunn-McCurdy Status âA demanifested sensorâ Climate Applications Total solar irradiance, spectral solar irradiance Mitigation Priority Tier 2 Post-Nunn-McCurdy, soundings are limited to the 01:30 NPOESS C1 orbit and 09:30 MetOp orbit. Considering both ascending and 24â d Â escending passes, there are alternating 4- and 8-hour intervals between measurements (i.e., 4 hours between the descending passes of C1 and MetOp, and then an 8-hour gap until the C1 ascending pass). Note that the C2 satellite as currently configured has no CrIS or ATMS sounder capability and thus would not be an effective replacement 25â for C1.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 45 FIGURE 3.7â Compared are measurements of total solar irradiance made by space-based solar radiometers since November 1978. The TIM on Glory is planned for overlap with TIM on SORCE. The demanifest of the TSIS sensor on NPOESS means that the total solar irradiance record will terminate at the end of the Glory mission. SOURCE: Courtesy of Judith L. Lean, Naval Research Laboratory. Figure 3.7.eps fixed image Highlights of Analysis Solar irradiance variability is the only external forcing of the climate system. Since atmospheric interference precludes its measurement with sufficient accuracy and precision from Earthâs surface, a space-based record is essential for specifying solar forcing of climate. Reliable knowledge of solar forcing is crucial because of its p Â otential to either mitigate or exacerbate anthropogenic warming. The current record of total solar irradiance extends uninterrupted since 1978 (Figure 3.7) and, although one of the longest continuous space-based climate records, covers less than three solar activity cycles. Composite 28-year time series (FrÃ¶hlich and Lean, 2004; see Figure 3.8) are constructed by accounting for differences in the uncer- tainties (absolute calibration) and repeatability (precision) of observations made by individual solar Âradiometers on many spacecraft.26 An uninterrupted irradiance record that extends over many (not just a few) solar activity cycles with sufficient precision to resolve long-term solar changes that may manifest from one activity cycle minimum to the next is needed to understand the Sunâs role in climate change. The magnitude of long-term solar irradiance changes is highly uncertain because the observational record is, thus far, too short to reliably detect possible Âcentennial-scale variations that may underlie the 11-year activity cycle. The committee notes the unique importance of a reliable, uninterrupted, long-term solar irradiance record for guiding policy by constraining external climate forcing to plausible limits. While the magnitude of solar forcing is expected to be considerably smaller than projected anthropogenic forcing in the next century (IPCC, 2007), empirical analysis of both recent and paleoclimate data caution that cli- mate system responses to solar forcing are by no means properly understood, and may involve a variety of indirect processes and natural climate oscillations. Because of the uncertainty regarding both long-term solar forcing and climate responses, the IPCCâs conclusions are not universally accepted; in fact, claims of significant solar-induced effects on climate are often reported in the public press as an alternative cause to global warming. Recent debate about the Sunâs role in global warming from 1980 to 2000 illustrates the type of ambiguity that can ensue when reliable climate-quality data are not available. During the period from about 1989 (after the reentry of the SMM missions with ACRIM I) to 1991 (before the launch of ACRIM II on UARS) only one radiometer, ACRIM I on SMM, ERB on Nimbus 7, ACRIM II on UARS, VIRGO on SOHO, ACRIM III on ACRIMSAT, and TIM on SORCE. 26â
46 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT (a) (b) FIGURE 3.8â Compared in the panel labeled (a) are the irradiance composites of Willson and Mordvinov (2003) (WM2003, red symbols) and FrÃ¶hlich and Lean (2004) (FL2004, green solid line). Their differences, shown in panel (b), have no significant trend between January 1981 and June 1989, nor after July 1992. The approximate 3-year jump from mid-1989 to mid-1992 pro- figure 3.8.a.b.eps fixed image duces higher irradiance levels in 1996 relative to 1986, which Scafetta and West (2005) assume to be an upward âtrend between minima during solar cycles 21-23â associated with a 22-year solar cycle. SOURCE: J.L. Lean, Comment on âEstimated solar contribution to the global surface warming using the ACRIM TSI satellite compositeâ by N. Scafetta and B.J. West. Geophys. Res. Lett. 33:L15701, doi:10.1029/2005GL025342, Copyright 2006 American Geophysical Union. on the Nimbus 7 spacecraft, sustained the total irradiance record. Unfortunately, that radiometer lacked in-flight sensitivity tracking and was further found to be susceptible to the platform environment (e.g., movement, thermal, power) in ways that were not adequately quantified. A composite record that assumes no instrumental drifts in the Nimbus 7 radiometer shows a shift between successive solar minima (in 1986 and 1996), which has been misÂ interpreted as an upward irradiance trend, even though, in reality, it is a jump (Figure 3.8), and thus more likely of instrumental rather than solar origin. The possibility of such an upward tend in recent decades has spawned studies attributing as much as 30 percent of recent global warming to solar irradiance. The issue remains under debate and the elimination of TSIS from NPOESS severely reduces the imminent resolution of this issue. As Earthâs only true external forcing, and with known variations arising from the Sunâs activity, inadequate knowledge of future solar forcing guarantees ambiguity in climate change attribution. The value of a reliable, uninterrupted record of solar irradiance extends well beyond the most visible and obvi- ous applications of climate change simulations and policy making regarding global warming. The external climate forcing quantified by a precise, continuous, long-term record of solar irradiance provides a unique opporÂtunity to
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 47 understand and characterize poorly known climate processes and sensitivity. Even after a decade of research and four IPCC assessments, uncertainties of climate sensitivity from all forcing mechanisms remain largely unchanged. From a climate modeling perspective, short-term climate sensitivities, such as to decadal forcing by the solar i Ârradiance cycle, are calculated to be so small in amplitude (and lagged by many years) as to be undetectable in the temperature record as a result of the long thermal time scales of the ocean response. However, an accumulating body of empirical evidence questions the legitimacy of this response scenario and suggests particularly that climate responses to solar radiative forcings are not yet fully understood. Continued measurements of the Sunâs 11-year cyclic behavior can improve modeled climate responses and reduce the uncertainties in forcing assessments. Global surface temperature changes that are in phase with the solar cycle are evident in both instrumental and space-based temperature records (e.g., Figure 3.9). They suggest that climate response to solar irradiance forcing involves dynamical motions within the atmosphere in addition to thermal processes. Both recent and paleoclimate data suggest that the hydrological cycle is especially sensitive and may involve ENSO- and NAO-like interactions (e.g., Shindell et al., 2006; Ammann et al., 2007; van Loon et al., 2004). The results are motivating improvements FIGURE 3.9â Four primary sources of global, monthly mean, surface temperature variations are shown in the top two panels, determined from multiple regression of the observed record. In the top panel, changes attributed to solar variability are com- pared with an upward trend, which tracks increasing3.9.eps fixed image--all text is outlined characters net forcing of greenhouse gas Figure concentrations of anthropogenic gases (the warming and tropospheric aerosol cooling). ENSO (light blue) and volcanic influences (dark blue) are compared in the middle panel. In the bottom panel, an empirical model that combines all four influences (solid dark line) is shown superimposed on the measured temperature anomalies (symbols). See also Lean (2005). SOURCE: Judith L. Lean, Naval Research Laboratory.
48 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT and expansions of the GCMs, which are typically not able to reproduce the empirical Sun-climate associations. Since the solar-induced surface temperature changes may be driven by a combination of direct visible-near IR solar forcing of the surface and troposphere, as well as solar UV-induced changes in stratospheric ozone, solar radiative forcing is a unique tool for deciphering the processes by which the surface and atmosphere interact in response to radiative forcing. A record of the spectral irradiance that composes the Sunâs total radiative output commenced in 2002 with SIM observations on SORCE. Although of much shorter duration, covering thus far only the descending phase of solar cycle 23, an uninterrupted time series of solar spectral irradiance is important to climate change research because solar radiative forcing and atmospheric and climate responses are all strongly wavelength dependent. In particular, variations in solar UV irradiance, which are an order of magnitude larger than the visible and near-IR changes, alter the ozone layer and stratosphere, forcing indirect climate change from stratospheric-tropospheric couplings. In pursuit of improved understanding and advanced capability, a new generation of general circulation climate models is being developed in which state-of-the-art representations of the stratosphere (for example, with upper height âlidsâ near 80 km and interactive ozone chemistry) replace the few âbufferâ (inactive) atmospheric lay- ers that represent stratospheric processes in most current GCMs (Rind et al., 2007). Time-dependent simulations with the new models require as input the actual solar spectral irradiance variations, taking into account the strong wavelength dependence of the variations rather than assuming that spectral irradiance variations are wavelength- independent, and simply mimic the total. In future IPCC and other assessments, spectral irradiance will likely be requisite inputs for GCM simulations since models that input simply total irradiance and lack proper stratospheres are clearly inadequate. A continued, uninterrupted record of solar spectral irradiance observations simultaneously with the longer, more precise total irradiance record is necessary to ensure that these inputs are reliable. Ironically, demanifesting TSIS from NPOESS terminates the solar irradiance record even as recognition of the potentially pervasive and subtle nature of climate responses to solar forcing is growing. Without TSIS on NPOESS, the total solar irradiance record will terminate after the flight of the total irradiance monitor (TIM) on Glory, which, based on its nominal 3-year mission duration, could occur as early as 2011. 27 The spectral solar ir- radiance record, which is provided via the spectral irradiance monitor (SIM), will also terminate at the end of the SORCE mission, which, as noted earlier, could occur after less than one solar cycle of observations. Lacking an ongoing, uninterrupted observational record, knowledge of solar forcing for climate simulations and attribution and assessment studies will need to be estimated from models of irradiance variations. These models are based on analysis of the current record, which is too short to quantify possible long-term trends. TSIS (Figure 3.10) is a fully mature, state-of-the-art solar irradiance sensor that measures both total and spectral (200 nm to 0.2 micron) irradiance. Both of its instrumentsâTIM and SIMâhave benefited significantly from the injection of cutting-edge technological advances; both have also been operating essentially flawlessly on SORCE since 2002.28 TSIS is relatively small and entirely self-contained; the bolometric devices used by both TIM and SIM are by design self-calibrating. Both TIM and SIM have multiply redundant components to account for in-fight sensitivity drifts. Extensive preflight calibration and characterizations are conducted, and neither ancillary data, nor formation flying is needed. Finding:â An uninterrupted record of measurement of solar irradiance is of unique value for both climate change science and for policy making. Solar irradiance was highly ranked in terms of providing a historical record of global climate, requirements for data continuity, and consequences of a data gap (question 1), measurement matu- rity (question 5), uniqueness (question 6), and use in development of synthesis products (question 7); however, it Gloryâs hydrazine propulsion module will contain enough fuel for at least 36 months of service. Note that the French PICARD mission 27â carries a total irradiance sensor that will fly from 2009-2011 and should overlap the operation of Glory. Advances include phase-sensitive signal detection, NiP black cavity surfaces, and NIST-measured apertures. See G. Kopp, G. Lawrence, 28â and G. Rottman, The Total Irradiance Monitor design and on-orbit functionality, in Telescopes and Instrumentation for Solar Astrophysics (S. Fineschi and M.A. Gummin, eds.), Proceedings of SPIE Volume 5171, SPIE, Bellingham, Wash., 2004, doi: 10.1117/12.505235, available at http://glory.gsfc.nasa.gov/publications/TIM_Paper.pdf.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 49 SIM 2008-2013 Glory FIGURE 3.10â The NPOESS/TSIS sensor comprising the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM) mounted on solar tracking platform (TPS). SOURCE: Courtesy of the TSIS team at the Laboratory for Atmospheric and Space Physics. Figure 3.10.eps received somewhat lower rankings on other factors, including its role in climate prediction (question 3),29 reanalysis (question 4), and usage in other disciplines (question 9). Overall, solar irradiance was prioritized in the second tier of climate science capabilities. Preferred Recovery Strategy and Other Mitigation Options The maturity, demonstrated longevity, and relatively minor payload accommodation requirements would appear to make TSIS ideally suited for integration with operational platforms such as NPOESS. However, if re- manifesting on NPOESS is not practicable, the committee prefers the strategy of flying TSIS on a series of small, independent, free-flying, solar-pointing spacecraft. This approach provides the flexibility to achieve the overlap necessary to secure a highly precise continuous solar irradiance record, while a dedicated Sun-pointing spacecraft offers several advantages over non-solar-pointing platforms.30 Flights of opportunity could also provide an effective mitigation strategy. With a solar pointing gimbal (re- quired to allow TSIS to point continuously towards the Sun), the small TSIS sensor is readily accommodated in a range of orbits. There are no external auxiliary requirements and rapid procurement is possible due to a fully mature design and active instrument team. However, relative to a dedicated free flyer, flights of opportunity have additional risk for a data gap from launch delays that may arise independently of TSIS (for example, by other instruments or the spacecraft). Finding:â While both total and spectral solar irradiance are important to climate science, the committee noted a higher relative priority for restoration of total solar irradiance compared to spectral solar irradi- ance. Of the two, total solar irradiance is a more mature, less complex, and less costly measurement. Further, it has a longer current climate data record at risk than spectral irradiance. Therefore, should funding constraints preclude development of both TIM and SIM components of the original TSIS suite, the committee recommends that measurement continuity of TIM be given the higher priority. This reflects committee member judgments regarding the range of variability in TSI and the sensitivity of predictions to such variability. 29â For example, it removes the need for the platform to carry a solar-pointing gimbal, which is approximately equal in mass and cost to the 30â TSIS sensor itself.
50 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Recommendation:â The agencies should consider use of an appropriate combination of small, low-cost satel- lites and flights of opportunity to fly TSIS (or at least TIM) as needed to ensure overlap and continuity of measurements of total solar irradiance. Aerosol Properties Related NPOESS Sensor APS Post-Nunn-McCurdy Status âA demanifested sensorâ Climate Applications Aerosol properties Mitigation Priority Tier 3 Highlights of Analysis Quantifying the effects of aerosols on the climate system remains a significant challenge. Among the most important aspects of this challenge is the need to globally monitor aerosol properties sufficiently well to determine aerosol climate forcing, which in turn requires knowledge of aerosol composition and size, and optical proper- ties such as optical depth and particle absorption over a sufficiently broad spectral range. Satellite techniques for monitoring these aerosol properties have slowly advanced, but significant challenges remain in converting the available information to accurate measures of aerosol radiative forcing. The physical basis for existing satellite aerosol remote sensing retrievals requires an unambiguous separation of the scattering by the atmosphere from the reflection of sunlight from the surface. Thus, most aerosol retrieval methods are applied over ocean surfaces away from sun glint, where uncertainties associated with the effects of surface reflection are generally small. While long-term records of some aerosol properties exist based on the POES Advanced Very High Resolution Radiometer (AVHRR) observations (e.g., Mishchenko and Geogdzhayev, 2007), the information available from these satellite observations is usually restricted to information only over oceans, and is limited to aerosol optical depth at a few selected spectral bands from which coarse information about particle size can also be inferred (Nakajima et al., 2001). Multichannel measurements from instruments like Terra and Aqua MODIS provide some improvement over the AVHRR observations. The multi-angle measurements of Terraâs Multi-angle Imaging SpectroRadiometer (MISR) (Diner et al., 1998), though limited in spectral coverage, offer yet additional capability over land that is not available from AVHRR, MODIS, and similar single-angle imagers. Measurement of the polarization of reflected sunlight provides the most powerful way of separating atmosphere and surface scattering effects. The Polarization and Directionality of the Earthâs Reflectances (POLDER) I, II, and III instruments (Deschamps et al., 1994) have illustrated the value of spectral polarimetery (DeuzÃ© et al., 2001). The addition of polarization information to multi-angular radiance measurements has been shown to further constrain aerosol chemical composition by providing the real part of the refractive index (Mishchenko and Travis, 1997) and provides increased sensitivity to scattering by small aerosols (Chowdhary et al., 2005). A combination of multi-angle, multispectral, and polarization capabilities thus provides the greatest potential to monitor aerosols from space with sufficient capability to determine aerosol climate forcings. This potential, however, is yet to be realized. Polarimetry data are unique in their ability to accurately monitor aerosol abundance and size over land due to the segregation of land and atmosphere polarization effects by comparing visible (0.4-0.7 Î¼m) and near-infrared (NIR: 0.7-1 Î¼m) polarization, which are sensitive to atmospheric aerosols, to shortwave infrared (SWIR: 1-2.5 Î¼m) polarization, which is relatively insensitive to atmospheric aerosols. The planned NASA Glory mission will carry the Aerosol Polarimetry Sensor (APS) to improve on current aerosol sensing platforms, by combining POLDER- like spectral multi-angular measurements with an order-of-magnitude improvement in polarization accuracy and precision, allowing substantial improvement in aerosol properties assessment. 31 The relatively large footprint of the instrument (approximately 5 km at nadir compared to 1 km or less for MODIS and VIIRS), however, 31â raises concerns about cloud contamination that can affect the interpretation of data in the vicinity of clouds. Cloud clearing for Glory will use
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 51 FIGURE 3.11â Summary of the principal components of the radiative forcing of climate change. All these radiative forcings result from one or more factors that affect climate and are associated with human activities or natural processes as discussed in the text. The values represent the forcings in 2005 relative to the start of the industrial era (about 1750). Human activities cause significant changes in long-lived gases, ozone, water vapor, surface albedo,image figure 3.11.eps fixed aerosols, and contrails. The only increase in natural forcing of any significance between 1750 and 2005 occurred in solar irradiance. Positive forcings lead to warming of climate and negative forcings lead to a cooling. The thin black line attached to each colored bar represents the range of uncertainty for the respective value. SOURCE: P. Forster, V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz, and R. Van Dorland, Changes in Atmospheric Constituents and in Radiative Forcing, FAQ 2.1, Figure 2, p. 136 in Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning, M. Marquis, K. Averyt, M.M.B. Tignor, H. LeRoy Miller, Jr., and Z. Chen, eds.), Cambridge University Press, Cambridge, U.K. and New York, N.Y., available at http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf. Aerosol direct forcings and aerosol indirect forcings via their effects on clouds have the largest uncertainty of all the principal components of the radiative forcing of climate change (Figure 3.11) and past uncertainties attached to aerosol forcings have allowed the fitting of models to historical temperature records using climate sensitivities from 2 to 5 K (or even larger) for a doubling of CO2 (Knutti et al., 2002). The APS instrument (together with model estimates of the anthropogenic fraction of aerosol optical depth) should considerably reduce the uncertainty associated with aerosol direct forcing. This should improve climate models because both the climate sensitivity high-spatial-resolution nadir-viewing cloud cameras carried on board the same satellite. The expected performance of APS was discussed at âGlory Science Advisory Team Meeting,â January 17-18, 2006, Boulder, Colorado (see http://lasp.colorado.edu/glory/meetings/2006/). Regard- ing retrieval of aerosol characteristics in the presence of clouds, see, for example, the following presentations: Michael Mishchenko, âGlory APS Science Overview,â Brian Cairns, âAPS Instrument,â and Yoram Kaufman, âSeparating Clouds from Aerosols.â
52 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT and the aerosol forcing have been uncertain, allowing models with high (low) climate sensitivity to be combined with large (small) negative aerosol direct forcing to fit the past temperature record. Finding:â The originally planned APS aerosol property measurements ranked in the third tier of climate priorities. This judgment is based on recognition of the high importance of aerosol property measurement in c Â limate science, tempered by the belief that the measurement remains a fertile area of active research with evolving measurement requirements. While aerosol properties ranked highest amongst the climate capabilities in terms of its role in climate prediction (question 3), its overall lower prioritization is largely due to lack of an existing data record or role in reanalysis, low measurement maturity, and need for ancillary data (questions 1, 4, 5, and 6). Preferred Recovery Strategy and Other Mitigation Options The committee strongly supports flight of APS on the NASA Glory mission. The experience gained with Glory APS should allow the capabilities of this instrument, especially with respect to its ability to monitor cloud properties, to be better defined. Recommendations: â¢ NASA should continue its current plan to fly the APS on Glory. â¢ NASA and NOAA should continue to mature aerosol remote sensing technology and plan for the development of operational instruments for accommodation on future platforms and/or flights of opportunity. Ocean Color Related NPOESS Sensor VIIRS Post-Nunn-McCurdy Status âA reduced coverage sensorâ Performance degradation is also expected Climate Applications Aerosols, ocean color Mitigation Priority Tier 3 Highlights of Analysis Monitoring of variability and change in the ocean ecosystems is a key part of a comprehensive climate o Â bserving systemâunderstanding the spatial and temporal changes in ocean biology is a critical component of the Earth system and is fundamental to diagnosing the interaction between the physical climate system and bioÂgeoÂ chemical cycles. Moreover, the oceanâs biological processes are expected to change dramatically in response to ocean acidification, declining sea ice, inputs of meltwater, and changes in upwelling regimes, blooms of harmful algae, and even responses to proposed bioengineered approaches for carbon sequestration involving ocean biology (e.g., iron fertilization). Imagery of water-leaving radiances in the visible and near-infrared wavelengths provides information about the space-time scale variability of the ocean, while derived products provide information about phytoplankton chlorophyll variability, and thus about ocean ecosystems. MODIS Aqua32 and SeaWiFS data have been fundamental to the development of the ocean color climate data record over the past decade, as both instruments offer the best ocean color and aerosol information from orbit In contrast to the experience of the Science Team for MODIS on the afternoon EOS Aqua platform, the MODIS Science Team for Terra has 32â yet to provide stable ocean color data products, despite many person years of effort, due to a variety of issues including failure of the pre-launch sensor characterization, substantial radiometric signal degradation on orbit (up to 40 percent), and limitations with the on-orbit calibration
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 53 available since the demise of the Coastal Zone Color Scanner (CZCS) sensor 10 years earlier. VIIRS specifications promise similar spectral coverage (no chlorophyll fluorescence band), spectral bandwidths, radiometric dynamic range, accuracy, sensitivity, and spatial resolution to MODIS and SeaWiFS. A VIIRS instrument was planned for each of the three orbits in the pre-Nunn-McCurdy NPOESS program: one on the early morning (5:30 AM local), mid-morning (9:30 AM local), and early afternoon (1:30 PM local) missions. However, the VIIRS measurements of particular interest to the ocean color community (Vis/NIR bands especially) will likely suffer from both reduced coverage due the loss of the NPOESS mid-morning orbit and the degraded accuracy from cross-talk among the Vis/NIR bands caused by an optical filter assembly which lowers the effective signal-to-noise ratio (SNR). Recent interactions between the ocean color scientific community and NASA (Siegel and Yoder, 2007, and response by S. Alan Sternâsee Appendix C) demonstrate community concern about these issues and government limitations to address them without additional funding and prioritization. The loss of the NPOESS 09:30 mid-morning orbit leaves only 05:30 terminator and 13:30 afternoon orbits. The terminator orbit offers little sun reflectance even over the âday sideâ of the terminator for aerosol and ocean color measurements, and is not suitable for ocean color, terrestrial, and many atmospheric applications. It is important to recognize that the remaining 13:30 orbit, while well suited for these measurements, was not intended to provide the sole measurement vantage point for ocean color because of the deleterious effects of sun glint over portions of the oceans caused by near-specular bright sun reflections masking ocean color signals as shown in Figure 3.12. 33 Unfortunately, in addition to the reduced coverage caused by the elimination of the 09:30 NPOESS orbit, the NPP VIIRS sensor has developmental manufacturing anomalies associated with spectral bands particularly criti- cal to both aerosol and ocean color measurements (Box 3.2). These are the visible and near-infrared (Vis/NIR) bands between 0.4 and 1 Î¼m within which optical cross-talk due to spectral filter manufacturing anomalies have compromised both their precision and accuracy for certain products. The 13:30 orbit NPP VIIRS sensor anomalies are not likely to be corrected,34 and the next opportunity for launch of an ocean color-compliant VIIRS sensor in a 13:30 orbit will be on NPOESS C1, which will launch no earlier than 2013. The current U.S. and international ocean color sensor capabilities are summarized in Table 3.1. The SeaWiFS instrument design life was reached in 2000, and the system was almost shut down years later. MODIS Terra reached its design life in 2004, and MODIS Aqua has also recently exceeded its design life. The earliest MODIS replace- ment will be VIIRS NPP, which is now scheduled for June 2010.35 Together, the loss of the 09:30 NPOESS orbit and the reduced VIIRS Vis/NIR spectral performance for NPP combine to severely degrade the quality of future VIIRS aerosol and ocean color data upon which the climate and science communities have come to depend from MODIS and SeaWiFS. With no action, it is very likely that MODIS and SeaWiFS will terminate operations years ahead of the first launch of a satisfactorily operating VIIRS sensor for ocean color, and even then the missing 09:30 orbit will create a roughly 50 percent reduction in temporal and spatial coverage (unless a suitable international ocean color capability complementary to VIIRS becomes available). Some current and future international sensors have similar specifications to the current NASA sensors, however stronger partnerships must be made to ensure that detailed instrumental characterization, including post-launch system. Past experiences with ocean color sensors have produced a set of requirements for achieving accurate ocean color imagery (McClain et al., 2006). As demonstrated with MODIS Terra, errors in the prelaunch quantification of these sensor attributes are almost impossible to resolve on orbit because their effects are convolved and can vary with solar and sensor viewing geometries. Difficulties with Terraâs ocean color measurements are also briefly summarized in Bryan Franz, NASA Ocean Biology Processing Group, âMODIS Terra Ocean Processing Status,â January 16, 2007, available at http://oceancolor.gsfc.nasa.gov/DOCS/modist_processing/. Well before either SeaWiFS or MODIS was launched, orbit simulations showed that two orbits were required to meet the ocean color 33â threshold globally as a function of time. Simulations demonstrated, as MODIS later proved, that observations from a single orbit (either 09:30 or 13:30) would suffer from large âoutageâ areas over the ocean surface. The simulations also demonstrated that obtaining data daily from both the 09:30 and 13:30 orbits would allow the vast majority of those areas masked by sun glint in one orbit to be viewable from the other so that the ocean color EDR could be met. The combination of both the 09:30 and 13:30 orbits was demonstrated to be essential to practical global ocean color observations. S. Alan Stern, associate administrator of the Science Mission Directorate, NASA Headquarters, letter to Drs. Siegel and Yoder, University 34â of California, Santa Barbara, dated November 20, 2007, reprinted in Appendix C of this report. The delay in NPP launch until June 2010 was announced by NOAA while this report was in preparation. This latest delay is to accom- 35â modate a slip in the schedule for delivery of the VIIRS instrument.
54 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT FIGURE 3.12â Moderate Resolution Imaging Spectroradiometer (MODIS) image of the Canary Islands. Sun glint is a signifi- cant impediment to ocean color retrieval coverage, âwashing outâ significant sectors of the orbital swathâunless mitigated through a tilting mechanism (as with SeaWiFS) or through multiple orbit planes. SOURCE: Courtesy of Courtesy of Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC. figure 3.12.eps originally a .jpg photo calibration/validation processing, are made available with the imagery. Obtaining consistent, climate-quality data from multiple ocean color satellite sensors requires a diverse suite of focused and closely coordinated activities including design and characterization of the sensor, collection of field data, and continued broad participation of the science community (McClain et al., 2006). Finding:â Overall, restoring VIIRS degraded ocean color capabilities ranked in the third tier of climate priorities. The ocean color science community has concluded that even if VIIRS meets its sensor specification, the data are not ideal to meet existing and future ocean biogeochemistry science requirements, and additional capability beyond VIIRS is desired to adequately address ocean biology science requirements (NASA OBBWG, 2006, p. 34). However, as indicated by the discussion above, the committee recognizes the importance of ocean color observations in a climate observing system. Research points to the need to resolve diurnal time scales in ocean temperature and air-sea heat exchanges because nonlinearities in the atmosphere, in the ocean, and in the coupled system lead to rectification of the fast time scales and because daily coupling of the ocean and atmosphere in coupled models is one source of the errors found in results from these models. Clearly, the threat to ocean ecosystems is significant, and establishing a climate record of the ecosystem via ocean color has merit. Ocean
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 55 BOX 3.2 VIIRS Performance and Measurement of Ocean Color The baseline uncorrected integrated filter assembly (IFA) currently tested on the NPP VIIRS instrument fails to meet basic Vis/NIR band sensitivity and accuracy requirements, thus causing the instrument to fail to support threshold ocean color EDR performance. Figure 3.2.1 shows the estimated accuracy, pre- cision, and uncertainty (APU) metrics for the 551 nm water leaving radiance (nLw) for the uncorrected NPP VIIRS, simulated based on the measured laboratory performance of the sensor in the specified band (because of the nature of the assumptions that were made, the actual performance could be worse than predicted). As water leaving radiance is very low over most of the globe illustrated by the large percentage of pixels with truth radiance below 10 watts per square meter per micron per steradian (W mâ2 Âµmâ1 srâ1), it is important that the sensor be able to meet accuracy and precision requirements below 10 W mâ2 Âµmâ1 srâ1. It is clear, however, in Figure 3.2.1, that both accuracy and precision exceed the 10 percent accuracy and 5 percent precision requirements. As both accuracy and precision exceed their requirements, and uncertainty is defined as the root-sum square of accuracy and precision, then the uncertainty requirement is also notÂ met. FIGURE 3.2.1â Accuracy, precision, and uncertainty (APU) metrics for the 551 nm water leaving radiance (nLw) for the uncorrected NPP VIIRS. SOURCE: K. Turpie, NASA GSFC, âCherry-Picked (CP) IFA or Baseline (BL) Integrated Filter Assembly (IFA)? Impact of optical crosstalk to Ocean Color EDRs by two problematic filter arrays,â Fourth Visible/Â 3.2.1.eps fixed image Infrared Imager/Radiometer Suite (VIIRS) Crosstalk Technical Interchange Meeting, August 1, 2007, NPOESS Integrated P Â rogram Office, Silver Spring, Md.
56 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT TABLE 3.1â Current Ocean Color Sensors and Capabilities Spectral Launch Swath Resolution Coverage Sensor Agency Satellite Date (km) (m) Bands (nm) Orbit COCTS CNSA HY-1B 04/11/2007 1400 1100 10 402-12,500 Polar (China) (China) CZI CNSA HY-1B 04/11/2007 500 250 4 433-695 Polar (China) (China) MERIS ESA ENVISAT 03/01/2002 1150 300/1200 15 412-1050 Polar (Europe) (Europe) MMRS CONAE SAC-C 11/21/2000 360 175 5 480-1,700 Polar (Argentina) (Argentina) MODIS-Aqua NASA Aqua 05/04/2002 2330 1000 36 405-14,385 Polar (USA) (EOS-PM1) MODIS-Terra NASA Terra 12/18/1999 2330 1000 36 405-14,385 Polar (USA) (EOS-AM1) OCM ISRO IRS-P4 05/26/1999 1420 350 8 402-885 Polar (India) (India) POLDER-3 CNES Parasol 12/18/2004 2100 6000 9 443-1,020 Polar (France) SeaWiFS NASA OrbView-2 08/01/1997 2806 1100 8 402-885 Polar (USA) (USA) NOTE: COCTS, Chinese Ocean Color and Temperature Scanner; CZI, Coastal Zone Imager; MERIS, Medium Resolution Imaging Spectrometer; MMRS, Multispectral Medium Resolution Scanner; MODIS, Moderate Resolution Imaging Spectroradiometer; OCM, Ocean Colour Monitor; POLDER-3, Polarization and Directionality of the Earthâs Reflectances; SeaWiFS, Sea-viewing Wide Field-of-view Sensor. SOURCE: Courtesy of the International Ocean Colour Coordinating Group, available at http://www.ioccg.org/sensors/current.html. color observations are strongly recommended to extend the measurement record, but in terms of the committeeâs climate ranking factors, restoration of VIIRS degraded capabilities was not scored among the highest priorities. Ocean color did not rate highly with respect to use in reanalysis (question 4), uniqueness (question 6), and use by IPCC and CCSP (question 7).36 Preferred Recovery Strategy and Other Mitigation Options The IPO and VIIRS team should continue to make all practical efforts to improve VIIRS performance to meet specifications and avoid the anticipated degradation in accuracy. To address reduced sensor coverage, the agencies should work with their international partners toward flying a more capable imager, of the class expected from a fully functional VIIRS, in the mid-morning orbit. This might include consideration of a VIIRS flight of opportu- nity aboard an international mission and/or cooperation on MERIS-2 or OCM-2 efforts. 37 A free flyer tailored to the needs of the ocean color community is another possibility; the benefits of this approach have been noted in several recent publications.38 With the maturation of coupled biophysical ocean models, we may look toward assimilation of ocean color, but it is not yet a routine 36â process. In contrast, physical variables are assimilated and essential to climate modeling. The need for a dedicated ocean color mission to accommodate instrument calibration and other needs was expressed at the June 2007 37â workshop and a community letter to NASA (Siegel and Yoder, 2007). Note that the present committeeâs analysis is based only on the relevance of the measurement/sensor to the needs of the climate science and applications communities. Ibid. Also see NASA OBBWG (2006). 38â
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 57 Recommendations: â¢ The NPOESS Integrated Program Office should consider any practical mechanisms to improve VIIRS performance for NPP and ensure that all specifications are met or exceeded by the launch of NPOESS C1. â¢ The agencies should ensure that adequate post-launch calibration/validation infrastructure is in place, including oversight by the scientific community (see Chapter 4), to ensure the production of viable ocean color imagery. â¢ address reduced sensor coverage, the agencies should work with their international partners To toward flying a fully functioning VIIRS or a dedicated sensor on a mission of opportunity in Sun- synchronous orbit. The agencies should also work with international partners to ensure community access to ocean color and ancillary calibration/validation data from international platforms during the gap likely to be experienced prior to launch of C1. Ozone Profiles Related NPOESS Sensor OMPS-Limb Post-Nunn-McCurdy Status âA demanifested sensorâ Now restored to NPP Climate Applications Ozone profiles Mitigation Priority Tier 3 Ozone profile measurements are needed to both monitor the ozone recovery process and understand the impacts of climate change on ozone layer recovery. The trend of increasing depletion of global stratospheric ozone observed during the 1980s and 1990s is no longer occurring; however, it is not yet clear whether these recent changes are indicative of ozone recovery due to the decrease in ozone-depleting gases associated with the implementation of the Montreal Protocol (Forster et al., 2007). Adequate vertical resolution is needed to resolve ozone structure in the lower stratosphere, where most halogen-related ozone depletion occurs. Several studies have shown that ozone changes in the tropical lower stratosphere are very important for both the magnitude and sign of ozone radiative forcing (Ramaswamy et al., 2001). Continued limb monitoring of ozone concentrations is required to estimate the vertical profile of ozone changes, which is needed to estimate climate forcing. Ozone limb measurements contribute to an understanding of ozone changes in the lower stratosphere and hence the adequacy of the Brewer-Dobson circulation in climate models.39 These models are not yet sufficiently robust to understand changes in water vapor and ozone in the lower stratosphere (so forcing beyond that associated with ozone could be improved if measurements of the ozone profile continue). OMPS-Nadir and OMPS-Limb were designed as an integrated instrument suite to meet both monitoring and climate science goals. The nadir viewing portion of OMPS provides total column and profile ozone measurements comparable to the TOMS instrument. However, nadir-viewing instruments lack sufficient vertical resolution and sensitivity to depict altitude-dependent processes associated with ozone recovery. OMPS-Limb was intended to complement the OMPS-Nadir measurements, providing higher fidelity vertical profile ozone data to continue and improve upon the daily global data produced by the current ozone monitoring limb-viewing systems, the Solar Backscatter Ultraviolet radiometer (SBUV)/2. The limb profile measurement together with total ozone was to provide strong constraints on the magnitude of the forcing. Post-Nunn-McCurdy, only the OMPS-Nadir portion of the originally planned OMPS suite is retained. While retention of OMPS-Nadir satisfies obligations under The Brewer-Dobson circulation pattern sets up between equator and pole in the winter hemisphere and results in column ozone distribu- 39â tions that are low in the tropics and high in the polar regions. Many models predict an increased circulation associated with an increase in greenhouse gases; see H.K. Roscoe, The BrewerâDobson circulation in the stratosphere and mesosphereâIs there a trend? Advances in Space Research 38(11):2446-2451, 2006.
58 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT the Montreal Protocol to monitor total ozone, climate science needs for continued and improved vertical profile measurements remain unmet. Although the continuity and overlap of ozone profile measurements have provided intercomparison opportu- nities for calibration in the past, such overlap may not be critical if flights of a freshly calibrated instrument are planned for the future (NRC, 2000). Finding:â Overall, ozone profiles ranked in the third tier of climate priorities. Ozone profiles ranked highly in measurement maturity (question 5), but low in terms of need for continuity, uniqueness, contribution to under- standing of the climate system, and contribution to other disciplines (questions 1, 6, 8, and 9). Preferred Recovery Strategy and Other Mitigation Options With the deletion of the OMPS-Limb sounder, no monitoring of ozone profile below the ozone peak (where most ozone depletion occurs) would be possible during the period when NPOESS and MetOp would operate. The committee supports the recommendation made by the NRC decadal survey to restore OMPS-Limb to NPP, and strongly endorses the agenciesâ commitment to finish integration and testing of the already-built NPP OMPS-Limb instrument. The committee further notes that OMPS was designed as an integrated instrument suite with common electronics; therefore, a cost-benefit analysis is warranted to determine whether the suite should be restored to additional NPOESS platforms based on the level of integration in the original instrument design. 40 Recommendation:â The committee supports current agency plans to reintegrate OMPS-Limb on NPP. The agencies should consider the relative cost/benefit of reintegration of OMPS-Limb capabilities for NPOESS platforms carrying OMPS-Nadir based on the degree of integration inherent in the instrumentâs original design. RATIONALE FOR PRIORITIZATION: GOES-R LOST CAPABILITIES Geostationary Advanced Hyperspectral Sounding Related GOES-R Sensor HES Current Status âA demanifested sensorâ Climate Applications High temporal resolution temperature and moisture profiles for process studies Mitigation Priority Tier 2 Geostationary sounders provide the capability of observing diurnal variation of climate variables including cloudiness, surface (sea and land) temperature, and atmospheric temperature and humidity. Although limited to regional (rather than global) coverage, the environmental space-time scales sampled by geostationary sounders strongly relate to climate change, including the frequency and intensity of severe weather (e.g., severe thunder- storms, flash flooding, hurricanes, winter storms). Spatial scales of 25 km or less and temporal scales of minutes to hours, best achieved from geostationary orbit, are needed to, for example, capture the evolution of the pre-convec- tive environment as circulations develop and as low-level moisture is advected into a region. Further, by monitoring spectrally resolved radiances for the same location, local zenith angle, and local time every day, regional water vapor budgets in the western hemisphere can be determined. This, in turn, could lead to an improved analysis of The NASA-NOAA report indicates that restoring OMPS-Limb capability to the OMPS is âcost-effective compared to alternative ap- 40â proaches.â As the committee was not provided any specific information on costs, and in any event is not using cost as a factor in its prioritiza- tion, a relative value assessment is considered beyond the scope of this report.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 59 local climates, and better projections. Winds derived from the current GOES system are an important contributor to contemporary reanalysis efforts. An advanced GEO sounder would provide better winds (and moisture) at more vertical levels, with improved height assignments, in future reanalysis projects. The fast processes of the climate system, such as the development of storms as part of Earthâs weather systems, integrate their effects to alter climate through a number of important mechanisms that are thought to be changing in time.41 The moistening of the upper troposphere associated with deep convection, for example, is believed to be changing over time in such a way as to accelerate the water vapor feedback (Soden et al., 2005). The utility of advanced IR sounders has been demonstrated for monitoring climatic changes in upper tropospheric moisture (Lerner et al., 2002). Pre-convective environment observing capabilities provided by a hyperspectral GEO sounder also directly support the forecasting of storms and the prediction of the character of storms (such as potential convective intensity and moisture availability, among other characteristics42) that are of substantial importance to these aspects of climate change. Operational soundings from GOES began with the GOES-I series of satellitesâinitiated with the VAS demonstration mission through the Operational Satellite Improvement Program (OSIP). 43 An advanced sounding capability has been advocated for many years to meet emerging needs in both climate and weather communities. 44 GOES-R was to carry an advanced sounder, HES, with hyperspectral capability to greatly improve upon previ- ous GOES sounders. The hyperspectral capability of an advanced GEO sounder would enable observation of the sources and sinks and the transport of pollutant and greenhouse gases, including CO 2, CO, O3, N2O, CH4, and H2O, and improve understanding of climate variability and change, while simultaneously providing benefits to society through superior weather analysis and forecasts. The termination of the sounder on GOES-R will instead end this long-term record after GOES-P. A geostationary hyperspectral sounder builds upon polar orbiting hyperspectral sounding experience gained from the currently operating AIRS and IASI instruments and planned NPOESS-era CrIS. Mesoscale models and assimilation systems have continued to advance to the point where the spatial and temporal resolution provided by hyperspectral sounding from GEO can be readily exploited. Capitalizing on geostationary orbitâs unique vantage point, a hyperspectral geostationary sounder would also provide an important data set for the intercalibration of 41â The source and sinks of anthropogenic radiatively active gases remain a primary concern in determining the extent of the effect of greenhouse gases on global climate. However, an equally important (yet poorly understood) influence on climate is the distribution of increased atmospheric water vapor associated with a speeding up of the hydrologic cycle. The atmospheric portion of the hydrologic cycle is complex, and operates on both short and long time scales. The fast processes associated with this mechanism, such as cloud formation and the related intra- and inter-cloud radiative impacts, influence cloud nucleation, longwave radiation, albedo feedbacks, and ultimately the surface energy balance. On decade to century time scales, the impact of increased water vapor is realized through alterations in large-scale cloud distribution, which reflect both the water-vapor distribution and the hydrologic cycleâs response. Also, the latent heating of clouds and its radiative effects influence the large-scale atmospheric circulation and hydrologic cycleâadditional complexities that need to be better understood. Excerpt from NRC, Decade-to-Century-Scale Climate Variability and Change: A Science Strategy, National Academy Press, Washington, D.C., 1998, p. 57. 42â The steering of tropical storms is generally governed by the adjacent environmental wind flow, which can often be cloudless, and defined by observations of the altitude-resolved motions of water vapor molecules. A geostationary hyperspectral sounder can help in the prediction of the initiation, or lack thereof, of tropical storm development in an otherwise relatively cloudless (or broken cloud) environment from its observations of sea-surface temperature, moisture, vertical shear of the horizontal wind, and often inhibiting Saharan Air Layer (Atlantic storms). It has been shown through adaptive observation modeling, that uncertainties and biases in hurricane landfall predictions (e.g., in the Gulf of Mexico) can be reduced through increased observations that are geographically remote (e.g., over Colorado or Greenland) 24-36 hours in advance. Through the use of many orthogonal vertical wind fields, retrieved through feature-tracking across many gridded water vapor profiles, significantly improved environmental wind fields can be assimilated into NWP models, resulting in improved predictability and forecast quality. 43â Prior to 1981, NASA and NOAA cooperated effectively in developing new operational satellite systems. At that time, NASA typically funded âfirst unitâ builds of weather satellites and their instruments and then transitioned proven capabilities to NOAA (and its predecessor, the Environmental Science Services Administration) for operational use. This cooperation was guided by a formal agreement established in 1973, the Operational Satellite Improvement Program (OSIP), which was funded at about $15 million per year. The budgets for NASA and NOAA reflected this agreement. NASA used its funding to develop prototype sensors, fly them on high-altitude aircraft, and transition them to research spacecraft for evaluation. Successful instruments were then provided to NOAA for transition to operational status. The program fell victim to NASA budget pressures and an Office of Management and Budget (OMB) desire to offload âroutineâ functions from NASA, and was canceled in 1982. See p. 51 of NRC (2003). 44â See, for example, Science Benefits of Advanced Geosynchronous Observations: (The Scientific Basis for the Advanced Geosynchronous Studies Program), Draft Report, March 1998. Available at http://goes.gsfc.nasa.gov/text/ags_science.html.
60 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT BOX 3.3 Geostationary Hyperspectral Sounding Benefits for Weather Applications In addition to nowcasting and short-term forecasting, our society increasingly relies on NWS 1- to 7-day forecasts for all aspects of public health and safety, transportation, agriculture policies, etc. The GEO ad- vanced sounder will contribute to improving the consistency and accuracy of the 1- to 7-day forecasts, giv- ing decision makers additional confidence with longer lead times. Specifically, an advanced GEO sounder would provide: â¢â Real-time continual pollution monitoring, severe storm warnings (e.g., tropical and convective), and avia- tion weather (e.g., visibility, icing, turbulence, volcanic ash, FAA NextGen 4D Weather Cube). â¢â Input to mesoscale NWP. â¢â Pre-convective conditions for heavy rainfall potential.1 â¢â Surface observationsâwith an increased probability of clear viewing of the sea (temperature, sea state) and land (temperature, vegetation index) and detection of diurnal signals. â¢â Atmospheric soundings with rapid refresh, providing improved atmospheric stability trends (pre-convec- tive storm outlooks). 1 Clouds are generally not a significant inhibitor for detecting the conditions antecedent to severe thunderstorm develÂ opment, as advanced geostationary IR sounding instruments would observe the thermodynamic changes (moisture flux, temperature lapse rate changes, and associated capping inversion erosion) which occur before the deep convection and opaque cloudiness takes place. Hyperspectral resolution can also allow observation of the thermodynamic structure below semi-transparent cirrus anvils, which often cover the sky after the convection is initiated, thereby making it pos- sible to observe where subsequent convection will take place. Finally, the higher spatial resolution of an advanced GEO sounder makes it possible to more frequently retrieve profiles between clouds and adjacent to fronts. While traditional IR-based sounders are inherently limited in their sounding abilities in cloudy regimes, the high spectral, spatial, and temporal capabilities of a hyperspectral sounder on a GEO platform would allow profiles above the cloud tops, and the potential for full profiles in broken cloud regimes. radiometers in low Earth orbit, as all polar satellites will under-fly it to provide the potential for 4-5 intercom- parisons per day. In addition to its role in observing the diurnal variation of climate variables, the incorporation of geostation- ary hyperspectral sounding capabilities on future GOES spacecraft would allow significant advances in weather analysis and forecasting (see Box 3.3). Noting the significant advances promised by the GEO hyperspectral sounder, members of the operational and research segments of the weather, water, climate, and environmental communities issued letters of support for an early flight for a GEO advanced sounder, and closure of the imminent GEO sounding gap. The National Weather Association (NWA) issued a Letter of Support for the GOES-R series high spectral resolution sounder, and the American Meteorological Societyâs Committee on Satellite Meteorology and Oceanography45 issued a consensus statement âOn the Importance of Deploying a GEO Advanced Sounder without Delay.â46 45â The AMS committee membership is found at http://www.ametsoc.org/stacpges/CommitteeDisplay/CommitteeDisplay.aspx?CC=SATMET. Chris Velden and Philip Ardanuy, members of the NRC committee authoring this report, also sit on the AMS committee. âGeostationary sounders provide unique, rapidly updated temperature and moisture profile measurements. The ability to vertically 46â resolve water vapor in the atmosphereâthe âbasic fuelâ for severe thunderstormsâis crucial for monitoring and predicting hazardous weather conditions. Large variations in atmospheric water vapor occur over fine scales of ten kilometers in the horizontal, one kilometer in the vertical, and over tens of minutes. Continuous monitoring is essential. Hyperspectral infrared measurements from GEO would con- tinuously describe the clear-sky vertical moisture structure, more than double the temperature profile information content from todayâs sounders, and permit new wind profiling capabilities by constantly tracking retrieved water vapor profile features at many discrete levels. Assimilated into the next generation of numerical weather prediction models and used for ânowcasts,â observations from the GEO advanced sounder could enable improved analyses of severe weather and hurricanes, with the potential to save lives while also providing important
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 61 Some of the recent difficulty in developing the Hyperspectral Environmental Sounder (HES) intended for GOES-R may be ascribed to the complexity of including coastal waters imagery requirements on top of those for hyperspectral infrared sounding. NOAAâs Analysis of Alternatives 47 included the possibility of flying just the advanced sounder portion of the HES suite. The analysis found that low-risk conceptual designs for an operational sounder exist and recommended a flight of a demonstration sounder as early as possibleâconceivably as early as 2012. The committee noted that while plans for international geostationary imaging missions were on a solid foun- dation, such was not the case for geostationary hyperspectral infrared sounding. The U.S. loss of initiative for providing geostationary hyperspectral soundings, even with the strong recommendations from the decadal survey, is disturbing; this loss of leadership48 is particular vexing as Europe, Japan, and China proceed with firm plans for geostationary hyperspectral sounding. Finding:â Provision of hyperspectral infrared sounding in GEO orbit ranked within the second highest tier of prioritized climate capabilities. The advanced sounder capability scored particularly high in terms of contributing to improved understanding in related disciplines (question 9) and measurement uniqueness (question 6). Preferred Recovery Strategy and Other Mitigation Options The preferred strategy for the recovery of advanced geostationary hyperspectral sounding is consistent with the decadal survey, NOAAâs Analysis of Alternatives, and community letters: an earliest possible flight of a dem- onstration mission in GEO orbit, followed by the earliest possible provision of sustained and robust operational GEO hyperspectral sounder seriesâbeginning no later than GOES-T. An early flight demonstration would serve to both realize the anticipated societal benefits in a timely and cost-effective fashion, and to prepare for the measurementâs operational transition. A proactive and cooperative effort between NASA and NOAA to develop a realistic demonstration plan is needed in order to prepare for the proposed operational GOES-T flight. The committee strongly encourages NOAA and NASA to partner together to demonstrate and complete development of this important observing capability. For example, a renewed NASA- NOAA partnership, perhaps through a mechanism similar to the Operational Satellite Improvement Program, could deliver an early hyperspectral demonstration sounder that could either be manifested on GOES-S or fly âin formationâ on a separate spacecraft, as EUMETSAT is considering for the hyperspectral sounder on the Meteosat Third Generation (MTG). An early flight of a sounder prototype for the GOES-R series would demonstrate both the technology and the measurement benefits, which could then be followed by an operational sensor on (or in formation with) GOES-T. Recommendation:â NASA and NOAA should plan an earliest-possible demonstration flight of a geostation- ary hyperspectral sounder, supporting operational flight in the GOES-T time frame. new climate observations. Other applications include the areas of aviation and air quality.â From, Satellite Meteorology and Oceanography Committee, AMS Scientific Activities and Activities Commission Consensus Statement, October 3, 2007. Available at http://www.eumetsat. int/idcplg?IdcService=GET_FILE&dDocName=PDF_MTG_MMT5. 47â See John J. Pereira, NOAA, Analysis of Alternatives for Advanced Sounding and Coastal Waters Imaging, presentation to committee on April 23, 2007, available at http://www7.nationalacademies.org/ssb/SSB_NPOESS2007_Presentations.html. A primary recommendation of the decadal survey is that âthe U.S. Government . . . renew its investment in Earth observing systems and 48â restore its leadership in Earth science and applicationsâ (NRC, 2007, p. 12).
62 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Geostationary Coastal Waters Imagery Related GOES-R Sensor HES-CWI Current Status âA demanifested sensorâ Climate Applications Ocean primary productivity and the carbon cycle Mitigation Priority Tier 4 The coastal ecosystem, at the boundary between land and ocean, is driven by climate-scale dynamics that af- fect both ocean and watershed processes. The coastal region is forced by diverse processes at multiple time scales, including tides (12- and 24-hour), diurnal heating (24-hour), and storm and other synoptic weather events, as well as long-term (climate trend) time scales. Deconvolving this superposition of the short and long time scales in coastal waters requires geostationary sampling. The Coastal Waters Imager (CWI) component of HES was to provide high temporal and spatial resolution observations, enabling improved water quality monitoring, coastal hazard as- sessment, navigation safety, ecosystem health awareness,49 natural resource management in coastal and estuarine areas, coral reef health monitoring, and development of nowcast and forecast models of the coastal ocean. With the cancellation of HES, coastal waters imagery capabilities in the GOES-R time frame were essentially lost. While the primary benefit of geostationary coastal waters imagery is to coastal monitoring, management, and remediation,50 there are important secondary benefits related to regional climate response that would be difficult to assess by any other means.51 These benefits are primarily associated with the higher temporal resolution afforded by use of a geostationary orbit, and higher spatial resolution intended for the CWI. Higher temporal resolution would serve to resolve rapid changes associated with climate-relevant processes (e.g., due to tides, coastal currents, and severe storms) and allow for more opportunities for cloud-free coastal waters viewing. CWIâs 300 m spatial resolution was intended to augment the existing long-term ocean color measurement record, extending it from open oceans and large basins into littoral regions, estuaries, and rivers to provide valuable measurements of coastal and shelf waters properties. These regions are currently undersampled due to the inability of current ocean color sensors, such as SeaWiFS, MODIS, and soon VIIRS, to resolve ocean color measurements on scales of 1 km or less, as well as their spectral inability to perform atmospheric corrections in these turbid regions. 52 CWIâs ability to dwell for long durations on areas of interest would allow for higher-quality images through improved signal- to-noise associated with longer integration times; higher quality images combined with higher spatial resolution would greatly enhance the ability to image and monitor complex areas like Chesapeake Bay, Puget Sound, San Francisco Bay, and the Great Lakes (see Figure 3.13). There is currently no capability, beyond limited point in situ data, for determining the sensitivity of the coastal regions to climate change. In its report to Congress, the U.S. Commission on Ocean Policy expressed growing concern about the health and future of coastal waters and noted the importance of spaceborne sensors to the Inte- grated Ocean Observing System (IOOS) (U.S. Commission on Ocean Policy, 2004). Geostationary coastal waters imagery would provide needed coastal monitoring and decision support capability, while also monitoring the ef- fects of climate change in coastal regions. CWI was to provide a resource for monitoring these climate-sensitive regions, including key indicators such as chlorophyll and related pigments, frequency and extent of harmful algal For example, CWI would provide critical observations on phytoplankton abundance and community structure in the coastal zone. 49â Storm events such as hurricanes can rapidly affect coastal water quality by suspending sediments and flooding rivers and estuaries with 50â nutrients and land-based pollution. Tides, winds (such as the land/sea breeze), river runoff, and upwelling can rapidly affect coastal regions through transportation of harmful algal blooms, pollution, and oil spills. Identifying and closely tracking these types of features as they ap- proach the shore would greatly improve the ability to manage coastal resources. Climate change in coastal waters may result in part from a greater frequency of storms and consequent runoff events, increasing the likeli- 51â hood of event-type responses, such as harmful algal blooms, which are best observed from a geostationary vantage point. Current sensors acquire one image per day and clouds and sun glint can obscure the view of an area. By sampling every three hours, coastal 52â waters imaging would provide coastal managers and scientists with access to coastal ocean imagery throughout the day, and the capability to choose or combine images to provide a view that is free of clouds. The Advanced Baseline Imager (ABI) on GOES-R could be used to select cloud free areas for imaging.
RECOMMENDED SHORT-TERM RECOVERY STRATEGY 63 FIGURE 3.13â Water clarity is a performance indicator for restoration efforts in the Chesapeake Bay. These images of the lower Chesapeake Bay illustrate the improvement in spatial resolution needed for coastal waters. The higher spatial resolution of the 250-meter Moderate resolution Imaging Spectroradiometer (MODIS) image (left) provides unmatched detail (turbid waters are shown in red; clear waters in blue) in the rivers and from the same sensor (right). SOURCE: Courtesy of Naval Research Laboratory; from âCoastal Waters Imaging on GOES-R: A Key Component of the Integrated Ocean Observing System,â available at http://cioss.coas.oregonstate.edu/CIOSS/Documents/GOESbrochure.pdf. Figure 3.13 blooms (HABs), and turbidity from changes in rainfall patterns and river flows. The GEO-CAPE mission, recom- mended for launch in the 2013-2016 time frame by the Earth Science and Applications from Space decadal survey (NRC, 2007), is intended to address many of these important coastal ecosystem observation needs, although it is fundamentally a research-driven mission rather than an operational capability. Finding:â In terms of climate prioritization, coastal waters imagery ranked in the lowest (fourth) prioritization tier. As a fundamentally new measurement, coastal waters imagery ranked highly for measurement uniqueness (ques- tion 6); however, it was ranked near the bottom of most other prioritization questions. This is perhaps unsurprising, as coastal waters imagery is primarily intended to serve other, non-climate applications and research needs. Preferred Recovery Strategy and Other Mitigation Options Provision for coastal waters imaging should be considered by the agencies based on non-climate applications. SUMMARY OF COMMITTEE RECOMMENDATIONS FOR NEAR-TERM RECOVERY The sections above summarize the impacts on the climate-related measurement capabilities of NPOESS and GOES-R that resulted from the June 2006 Nunn-McCurdy certification of NPOESS and the decision in September 2006 to eliminate HES on GOES-R. In Chapter 2 the committee details its prioritization process, which resulted in an ordered list of the importance of these changes. In Table 3.2, the committee summarizes its recommendations for a near-term strategy to restore the climate capabilities that were endangered by the program restructurings.
64 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT TABLE 3.2â Summary Recommendations for Mitigation of Lost or Degraded Climate Capabilities Lost or Degraded Climate Capability in NPOESS Low Earth Orbit Recommendation Tier 1 Microwave Radiometry â¢â NASA and NOAA should initiate a study as soon as practicable to address continuity of microwave radiometry and to determine a cost-effective approach to supplement the AMSR-2, carried on the Japanese spacecraft GCOM-W, with another microwave radiometer of similar design. The agencies should also consider the feasibility of manifesting a microwave radiometer on a flight of opportunity or free flyer to cover the microwave radiometry gap anticipated with a delay in accommodation of MIS until NPOESS C2. â¢â The agencies should provide funding for U.S. participation in an AMSR-2 science team to take full advantage of this upcoming microwave radiometer mission. â¢â The NPOESS Integrated Program Office should continue with its plans to restore a microwave sounder to NPOESS C2 and subsequent platforms, with an emphasis on SUAG priorities 1 through 3 (core radiometry, sounding channels, and soil moisture/sea surface temperature). â¢â NASA and NOAA should devise and implement a long-term strategy to provide sea-surface wind vector measurements. The committee finds important limitations in the planned reliance on a polarimetric radiometer for this measurement; instead, the preferred strategy is timely development and launch of the next-generation advanced scatterometer mission, that is, the Extended Ocean Vector Winds Mission (XOVWM) recommended in the 2007 NRC decadal survey Earth Science and Applications from Space. Radar Altimetry A precision altimetry follow-on mission to OSTM/Jason-2 (i.e., Jason-3) should be developed and launched in a time frame to ensure the necessary mission overlap. The agenciesâ long-term plan should include a series of precision altimetry free flyers in non-Sun-synchronous orbit designed to provide for climate-quality measurements of sea level. Earth Radiation Budget To minimize the risk of a potential data gap, the committee reiterates the recommendation of the 2007 Earth Science and Applications from Space decadal survey to manifest the CERES FM-5 on NPP. The agencies should further develop an ERB instrument series and provide for subsequent flights on Sun-synchronous platforms to continue the Earth radiation budget long- term record. Tier 2 Hyperspectral Diurnal Coverage The CrIS/ATMS instrument suite should be restored to the 05:30 NPOESS orbit to provide improved hyperspectral diurnal coverage and support atmospheric moisture and temperature vertical profile key performance parameters. Total Solar Irradiance The agencies should consider use of an appropriate combination of small, low-cost satellites and flights of opportunity to fly TSIS (or at least TIM) as needed to ensure overlap and continuity of measurements of total solar irradiance. Tier 3 Aerosol Properties â¢â NASA should continue its current plan to fly the APS on Glory. â¢â NASA and NOAA should continue to mature aerosol remote sensing technology and plan for the development of operational instruments for accommodation on future platforms and/or flights of opportunity. Ocean Color â¢â The NPOESS Integrated Program Office should consider any practical mechanisms to improve VIIRS performance for NPP and ensure that all specifications are met or exceeded by the launch of NPOESS C1. â¢â The agencies should ensure that adequate post-launch calibration/validation infrastructure is in place, including oversight by the scientific community, to ensure the production of viable ocean color imagery. â¢â address reduced sensor coverage, the agencies should work with their international To partners toward flying a fully functioning VIIRS or a dedicated sensor on a mission of opportunity in Sun-synchronous orbit. The agencies should also work with international partners to ensure community access to ocean color and ancillary calibration/validation data from international platforms during the gap likely to be experienced prior to launch of NPOESS C1. Ozone Profiles The committee supports current agency plans to reintegrate OMPS-Limb on NPP. The agencies should consider the relative cost/benefit of reintegration of OMPS-Limb capabilities for NPOESS platforms carrying OMPS-Nadir based on the degree of integration inherent in the instrumentâs original design. Lost or Degraded Climate Capability in GOES-R Geostationary Earth Orbit Recommendation Tier 2 Geostationary Hyperspectral Sounding NASA and NOAA should plan an earliest-possible demonstration flight of a geostationary hyperspectral sounder, supporting operational flight in the GOES-T time frame. Tier 4 Geostationary Coastal Waters Imagery Provision for coastal waters imaging should be considered by the agencies based on nonâclimate applications.
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