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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring 3 Recommended Short-Term Recovery Strategy In this chapter, the committee presents a summary of the analysis that informed its recommended prioritization.1 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.2 The text in this chapter provides highlights of the factors that informed the committee’s ranking; however, it is not meant to be an exhaustive summary of the information considered by the committee.3 RATIONALE FOR PRIORITIZATION: NPOESS LOST CAPABILITIES Microwave Radiometry 1 The process by which the committee performed its prioritization is discussed in Chapter 2; the priorities are based on an average of each member’s 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. 2 See especially the report of the June 2007 workshop (NRC, 2008; reprinted in Appendix B) and Earth Science and Applications from Space: 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). 3 Some of the material in this chapter was revised and/or extended after the ranking process was completed. These changes improved the clarity and depth of the analyses in this chapter; they did not, however, alter the committee’s findings shown here.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring Highlights of Analysis Satellite microwave (MW) radiometry has a 35-year heritage of providing highly accurate geophysical retrievals 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 Earth’s 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.4 The alteration of the planet’s 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 planet’s 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. Additional 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 hurricanes are in part determined by the availability of oceanic heat to sustain, encourage, or dissipate these storms. Climate oscillations such as the El Niño 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 Sensor 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 +/− 2.9 percent per decade over the period 1979-2006 (Serreze et al., 2007). Snow cover in the Northern Hemisphere has also declined by 1.28 × 106 km2 over the period 1972-2006 (Déry and Brown, 2007).5 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. 4 Monitoring water vapor via its emission at 22.235 GHz, the MW radiometer provides the most accurate means to measure total columnar 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. 5 In the IPCC 4th Assessment it is stated that “continuous satellite measurements capture most of the Earth’s seasonal snow cover on land, 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 precipitation” (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 during spring and summer (Brodzik et al., 2006).
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring As has been demonstrated via WindSat,6 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 CO2 uptake). As such, characterization and quantification of the role of the global ocean as a planetary heat and carbon sink depend critically on accurate 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 NASA’s QuikSCAT. The differences are even more dramatic when comparing the capabilities of passive radiometers (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.7 XOVWM’s 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 2.5 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 corresponding backscatter to infer surface wind speed and direction over water surfaces. SVW retrievals from scatterometer observations 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, designated 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 6 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. 7 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. See also Z. Jelenak, P.S. Chang, J. Sienkiewicz, R. Knabb (NOAA), and D. Chelton (Oregon State University), “Current and Future Needs and Solutions for Ocean Surface Vector Wind Measurements from Space,” presentation to the committee, June 20, 2007, available at www7.nationalacademies.org/ssb/NPOESSWorkshop_NRC_Workshop_June07_zjelenak.pdf; Freilich and Vanhoff (2006), and Monaldo (2006). Also of interest regarding XOVWM versus QuikSCAT and WindSat are presentations given at the NOAA Operational Satellite SVW Winds Requirements Workshop on June 5-7, 2006; available at http://manati.orbit.nesdis.noaa.gov/SVW_nextgen/workshop_outline.html.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring BOX 3.1 SUAG Priorities Core Radiometry Channels (10-89 GHz) Sounding Channels (50-60, 166 and 183 GHz) Soil Moisture/Sea Surface Temperature (6 GHz) Wind Direction (10-37 GHz polarimetric channels) 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).8 This would be a deviation from the NPOESS Science User Advisory Group (SUAG)9 recommendations (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 sounding 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 JAXA’s GCOM-W platform, but not before 2012, and no follow-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 65 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 committee’s view, this would be devastating to climate monitoring of SST and the hydrologic cycle. Given the importance of the MW radiometer for climate monitoring, the committee found cancellation of CMIS on the 8 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 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 “The Future of NPOESS: Results of the Nunn-McCurdy Review of NOAA’s Weather Satellite Program,” 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. 9 The SUAG represents the primary U.S. government users of NPOESS data. See Memorandum of Agreement Between the Department of Commerce, Department of Defense, and National Aeronautics and Space Administration for the National Polar-Orbiting Operational Environmental 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. 11 The GPM Microwave Imager (GMI) is NASA’s key contribution to the U.S.-Japanese Global Precipitation Mission, which is scheduled for launch in 2013.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring NPOESS C1 platform both puzzling and ill advised. CMIS represented the state of the art in satellite MW radiometers 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 measurements of the changing hydrologic cycle made it a unique and essential sensor for climate. In the committee’s 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: 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 reanalysis (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 desirable, 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: Adding C-band channels to NASA’s GMI instrument, and enlarging its antenna.13 Although GMI’s orbit inclination of 65° is not ideal for ocean monitoring, it is sufficient to view most ocean areas. 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: 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. 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. 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). 12 U.S. Climate Change Science Program, “Strategic Plan for the Climate Change Science Program,” available at http://www.climatescience.gov/. 13 Without the C-band channels, accurate SST measurements cannot be obtained for SST less than 12C. This excludes a large portion of the world’s oceans.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring 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 forecasting needs. Considering the advanced capabilities of XOVWM as compared to the QuikSCAT-type scatterometer (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: 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 Highlights of Analysis Sea level is a fundamental indicator of changes in Earth’s 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 variations to “climate-like” 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 14 While other satellite altimeter measurements had previously flown, they either did not have the instrument or orbit determination precision (Seasat, Geosat), and/or they flew in Sun-synchronous orbits (e.g., ERS, Envisat) that are undesirable for climate research and applications. 15 Overlap between the missions is critical for assessing instrument performance, differences between instruments, and other factors that vary from one mission to the next.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring FIGURE 3.1 Global mean sea level variations (mm) from the TOPEX/Poseidon and Jason-1 missions. SOURCE: Courtesy of Centre National d’Etudes 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 “fingerprints” 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 “operational” 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 accelerating—ultimately 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 including 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 Note added in proof: The present report was completed before the successful launch of OSTM/Jason-2 on June 20, 2008.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring FIGURE 3.2 Sea level (from Jason-1 and TOPEX/Poseidon) in the Pacific averaged over 5S-5N, 210-270E (bottom) and as a change map (Jason-1 data only, top). SOURCE: Courtesy of L. Fu/NASA/JPL. 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 17 ECCO is the acronym for Estimating the Circulation and Climate of the Ocean; SODA is the acronym for Simple Ocean Data Assimilation.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring FIGURE 3.3 Trends (mm/year) in sea level change over 1993-2007 from TOPEX/Poseidon and Jason-1 altimeter measurements. SOURCE: Courtesy of Colorado Center for Astrodynamics Research, University of Colorado at Boulder. For more information, 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. 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 measurements 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.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring Finding: 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 committee’s 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 (66° 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 “wide-swath” 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. While other altimeter missions 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: 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 agencies’ 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 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. NASA’s Earth Radiation Budget Experiment provided the second generation 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 Earth’s 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 Earth’s surface. Through synergies with simultaneous measurements by other EOS instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS), it is possible to relate cloud
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring FIGURE 3.4 (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 of NASA/Goddard Space Flight Center Scientific Visualization Studio, available at http://visibleearth.nasa.gov/view_rec.php?id=11907.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring Recommendations: 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. 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. To address reduced sensor coverage, the agencies should work with their international 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 C1. Ozone Profiles 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 39 The Brewer-Dobson circulation pattern sets up between equator and pole in the winter hemisphere and results in column ozone distributions 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 Brewer−Dobson circulation in the stratosphere and mesosphere—Is there a trend? Advances in Space Research 38(11):2446-2451, 2006.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring 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 opportunities 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: 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 understanding 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 agencies’ 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: 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 instrument’s original design. RATIONALE FOR PRIORITIZATION: GOES-R LOST CAPABILITIES Geostationary Advanced Hyperspectral Sounding 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 thunderstorms, 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-convective 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 40 The NASA-NOAA report indicates that restoring OMPS-Limb capability to the OMPS is “cost-effective compared to alternative approaches.” As the committee was not provided any specific information on costs, and in any event is not using cost as a factor in its prioritization, a relative value assessment is considered beyond the scope of this report.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring 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 Earth’s 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 satellites—initiated 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 previous 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 CO2, 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 orbit’s unique vantage point, a hyperspectral geostationary sounder would also provide an important data set for the intercalibration of 41 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 cycle’s response. Also, the latent heating of clouds and its radiative effects influence the large-scale atmospheric circulation and hydrologic cycle—additional 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. 42 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. 43 Prior to 1981, NASA and NOAA cooperated effectively in developing new operational satellite systems. At that time, NASA typically funded “first unit” 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 “routine” functions from NASA, and was canceled in 1982. See p. 51 of NRC (2003). 44 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.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring 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 advanced sounder will contribute to improving the consistency and accuracy of the 1- to 7-day forecasts, giving decision makers additional confidence with longer lead times. Specifically, an advanced GEO sounder would provide: Real-time continual pollution monitoring, severe storm warnings (e.g., tropical and convective), and aviation weather (e.g., visibility, icing, turbulence, volcanic ash, FAA NextGen 4D Weather Cube). Input to mesoscale NWP. Pre-convective conditions for heavy rainfall potential.1 Surface observations—with an increased probability of clear viewing of the sea (temperature, sea state) and land (temperature, vegetation index) and detection of diurnal signals. Atmospheric soundings with rapid refresh, providing improved atmospheric stability trends (pre-convective storm outlooks). 1Clouds are generally not a significant inhibitor for detecting the conditions antecedent to severe thunderstorm development, 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 possible 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 intercomparisons per day. In addition to its role in observing the diurnal variation of climate variables, the incorporation of geostationary 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 Society’s Committee on Satellite Meteorology and Oceanography45 issued a consensus statement “On the Importance of Deploying a GEO Advanced Sounder without Delay.”46 45 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. 46 “Geostationary sounders provide unique, rapidly updated temperature and moisture profile measurements. The ability to vertically resolve water vapor in the atmosphere—the “basic fuel” for severe thunderstorms—is 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 continuously describe the clear-sky vertical moisture structure, more than double the temperature profile information content from today’s 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 “nowcasts,” 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
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring 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. NOAA’s Analysis of Alternatives47 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 possible—conceivably as early as 2012. The committee noted that while plans for international geostationary imaging missions were on a solid foundation, 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: 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, NOAA’s Analysis of Alternatives, and community letters: an earliest possible flight of a demonstration mission in GEO orbit, followed by the earliest possible provision of sustained and robust operational GEO hyperspectral sounder series—beginning 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 measurement’s 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 “in formation” 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: NASA and NOAA should plan an earliest-possible demonstration flight of a geostationary hyperspectral sounder, supporting operational flight in the GOES-T time frame. new climate observations. Other applications include the areas of aviation and air quality.” 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. 47 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. 48 A primary recommendation of the decadal survey is that “the U.S. Government … renew its investment in Earth observing systems and restore its leadership in Earth science and applications” (NRC, 2007, p. 12).
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring Geostationary Coastal Waters Imagery The coastal ecosystem, at the boundary between land and ocean, is driven by climate-scale dynamics that affect 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 assessment, 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. CWI’s 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 CWI’s 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 Integrated 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 effects 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 49 For example, CWI would provide critical observations on phytoplankton abundance and community structure in the coastal zone. 50 Storm events such as hurricanes can rapidly affect coastal water quality by suspending sediments and flooding rivers and estuaries with 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 approach the shore would greatly improve the ability to manage coastal resources. 51 Climate change in coastal waters may result in part from a greater frequency of storms and consequent runoff events, increasing the likelihood of event-type responses, such as harmful algal blooms, which are best observed from a geostationary vantage point. 52 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 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.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring FIGURE 3.13 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 “Coastal Waters Imaging on GOES-R: A Key Component of the Integrated Ocean Observing System,” available at http://cioss.coas.oregonstate.edu/CIOSS/Documents/GOESbrochure.pdf. blooms (HABs), and turbidity from changes in rainfall patterns and river flows. The GEO-CAPE mission, recommended 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: 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 (question 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.
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Ensuring the Climate Record from the NPOESS and GOES-R Spacecraft: Elements of a Strategy to Recover Measurement Capabilities Lost in Program Restructuring TABLE 3.2 Summary Recommendations for Mitigation of Lost or Degraded Climate Capabilities
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