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Appendix A Past, Present, and Planned Sensors Past Sensors Coastal Zone Color Scanner (CZCS) Sensor/Satellite Agency Mission Duration Swath Resolution Bands Spectral Coverage (nm) CZCS NASA (USA) 1978-1986 1,556 km 825 m 6 433-12,500 case of failure and was calibrated using the instrument itself. Sensor Description: The light from the lamp was used only to verify instrument The CZCS was the first satellite sensor devoted to ocean stability with time. The calibration revealed the degradation color imaging. Out of six spectral bands, four were used of the sensitivity in the visible bands (Evans and Gordon, primarily for ocean color. These four bands were centered 1994). The vicarious calibration was conducted using post- at 443, 520, 550, and 670 nm with a 20-nm bandwidth. The launch validation cruises and the chlorophyll time-series mission goal was to test whether satellite remote sensing from Bermuda. could be used to identify and quantify suspended and dis- solved material in the surface ocean. The sensor successfully Data Availability: demonstrated that ocean color could be used to quantify chlo- rophyll and sediment concentrations in the ocean. It provided CZCS data are freely accessible. the justification for SeaWiFS and MODIS. Applications: Calibration: CZCS data were used to demonstrate the feasibility of The instrument was calibrated pre-launch. The on-orbit ocean color remote sensing and its application to measuring calibration was to have been accomplished by a built-in global phytoplankton biomass and productivity. Because of incandescent light source. The light source was redundant in the limited power, it could operate only a few hours per day. 79
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80 APPENDIX A Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) Sensor/Satellite Agency Mission Duration Swath Resolution Bands Spectral Coverage (nm) SeaWiFS NASA (USA) 1997-2010 2,806 km 1,100 m 8 402-885 Sensor Description: Data Availability: Data can be freely and openly accessed.1 Global data are The SeaWiFS mission was launched by the Orbital Sciences Corporation in 1997. It was a medium-spectral freely distributed at Level 1 (TOA total radiances in eight r esolution imaging spectroradiometer operating in the bands), Level 2 (geophysical products such as the spectral visible to near-infrared spectral range, aboard the polar marine reflectances and the chlorophyll concentration), and sun-synchronous OrbView-2 (OV-2) satellite. The sensor Level 3 (global gridded products). collected data in eight spectral bands (see Chapter 4; Table 4.5) from 402 to 885 nm. The instrument tilted ±20 degrees Applications: to minimize sun glint. The NASA Ocean Color Group distributes the following products, which are used for a large array of applications Calibration: described in Chapter 2: SeaWiFS mission used MOBY water-leaving radiances Radiances at 412, 443, 490, 555, 670 nm; aerosol opti- for the vicarious calibration and near-monthly lunar looks cal thickness at 865 nm; epsilon of aerosol correction at to track spectral band degradation over time. The mission 765 and 865 nm; OC4 Chlorophyll a concentration; diffuse included an extensive calibration/validation program using attenuation coefficient at 490 nm; Angstrom coefficient, 510- global in situ measurements for product validation. 865 nm; Photosynthetically Active Radiation from the sun 400-700 nm; Normalized Difference Vegetation Index; Land Reflectance and a SeaWiFS Biosphere product. 1 See http://oceancolor.gsfc.nasa.gov/. GLI Sensor/Satellite Agency Launch Date Swath (km) Resolution (m) Bands Spectral Coverage (nm) GLI/ADEOS II NASDA (Japan) 2002-2003 1,600 250/1,000 36 375-12,500 Sensor Description: Calibration: The Global Imager (GLI) was launched in 2002 aboard Vicarious calibration was performed. Results of vicari- ous calibration workshop are available online.2 ADEOS II, which also carried POLDER-2 [Polarization and Directionality of the Earth’s Reflectances]. GLI is designed to provide frequent global observations of reflected radiance Data Availability: of the ocean, clouds, and land. The sensor has a multi-spec- Data products are available online.3 tral observation capability with 36 bands and ground reso- lution of 1 km. Some channels have a resolution of 250 m. Applications: Ocean color, water-leaving radiances and aerosols. 2 See http://suzaku.eorc.jaxa.jp/GLI/cal/index.html; accessed October 25, 2010. 3 See http://www.eorc.jaxa.jp.
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81 APPENDIX A Current Sensors in Polar Orbit Moderate Resolution Imaging Spectroradiometer (MODIS) on TERRA and AQUA Ocean Color Spectral Coverage Sensor/Satellite Agency Launch Date Swath Resolution Bands (nm) MODIS (Terra) NASA (USA) 1999 2,330 250/500/1,000 9 405-14,385 MODIS (Aqua) NASA (USA) 2002 2,330 250/500/1,000 9 405-14,385 Sensor Description: More recently, SeaWiFS imagery also had to be used to address sensor degradation issues.4 MODIS is a key instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites designed for land, atmosphere, and ocean observations. Terra’s orbit around Earth is timed Data Availability: so that it passes from north to south across the equator in the All data and products (Levels 0-4) are freely available morning, while Aqua passes south to north over the equator online5 via network download. Products: Normalized water- in the afternoon. MODIS-Terra and MODIS-Aqua are view- leaving radiance at 412, 443, 488, 531, 551, and 667 nm; ing the entire Earth’s surface every one to two days, acquiring aerosol optical thickness at 869 nm; epsilon of aerosol cor- data in 36 spectral bands, or groups of wavelengths. rection at 748 and 869 nm; diffuse attenuation coefficient at 490 nm; Angstrom coefficient, 531-869 nm; and sea surface Calibration: temperature. MODIS is calibrated using a combination of solar and lunar viewing to track spectral calibration and temporal Applications: degradation as well as vicarious calibration using in situ MODIS serves a large array of applications including observations of water-leaving radiance. process and climate research and many resource managment applications. 4 See http://www.opticsinfobase.org/abstract.cfm?uri=ao-44-26-5524. 5 See http://oceancolor.gsfc.nasa.gov/. MERIS Instrument, on Board the ENVISAT Platform Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) MERIS ESA (Europe) 2002 1,150 300/1,200 15 412-900 Sensor Description: 4 × 4 pixel averaging (reduced-resolution products). Global coverage is obtained in three days (irrespective of clouds MERIS is an ESA-led mission (Rast and Bézy, 1995; and sun glint). Rast et al., 1999). It is a medium resolution imaging spectro- radiometer operating in the visible to near-infrared spectral Stability Monitoring: range, aboard the sun-synchronous ENVISAT platform. It is set up with 15 spectral bands from 412 to 900 nm. MERIS Radiometric calibration uses two onboard solar dif- is a “push-broom” spectrometer, with linear CCD arrays fusers. Spectralon is a very good reflectant with very providing spatial sampling in the across-track direction, well-characterized reflectance characteristics. Spectralon while the satellite’s motion provides scanning in the along- is subject to reflectance change over time after cumulative track direction. The MERIS field of view is 68°5 around exposure to solar radiance, in particular to ultraviolet expo- nadir, which gives a swath width of 1,150 km covered by sure. Because frequent solar views are required to monitor five identical optical modules (cameras) arranged in a fan the sensor stability, the degradation of the Spectralon also shape configuration. The spatial resolution at nadir is 300 must be monitored. Therefore, the first diffuser is used every m (full resolution products), and is degraded to 1.2 km by a two weeks for routine calibration, and the second one is used
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82 APPENDIX A every three months and therefore tracks possible degradation The higher spatial resolution of MERIS resolves coastal of the first one. An erbium-doped diffuser is used for spectral features such as plumes and fronts that are not evident in the calibration. MERIS was launched in May 2002 for an initial coarser resolution of the NASA sensors. The higher spectral and nominal five-year mission, which has been extended so resolution of MERIS enables more sophisticated algorithms that operations should continue through 2013. for complex coastal waters. The Naval Research Laboratory at Stennis Space Center is currently using full resolution MERIS imagery to support assimilation of satellite-derived Data Availability: optics into ocean models that provide forecasts on time scales Open access. Global data are freely distributed at Level of 24-48 hours. NOAA is now acquiring MERIS high spatial 1 (TOA total radiances in 15 bands), Level 2 (geophysical resolution imagery in near-real time (ca. 12 hours) for U.S. products such as the spectral marine reflectances and the coastal waters. NOAA’s Center for Coastal Monitoring and chlorophyll concentration), and Level 3 (global gridded Assessment (CCMA) is using MERIS imagery to assess and products). forecast coastal and marine ecosystem conditions, including for harmful algal bloom (HAB) forecasts. During summer 2010, CCMA had operational programs to detect cyanobac- Applications: teria and other HAB organisms in Lake Erie, Chesapeake MERIS radiometric capabilities were set up in the 1990s Bay, and Florida coastal waters. According to NOAA’s Dr. to meet predefined requirements for ocean color remote Richard Stumpf, the MERIS “red bands” (centered at 620, sensing (e.g., Gordon, 1987, 1988, 1990, 1997; Antoine 665, 680, and 709 nm) are particularly useful for CCMA and Morel, 1999). The onboard devices have proven very HAB forecasts. There also is high potential for using these efficient in maintaining a high radiometric accuracy and red bands as an alternative approach for retrieving chloro- stability. phyll in coastal waters. Algorithms based on these four bands With respect to coastal applications, the current MERIS are substantially unaffected by atmospheric correction errors. instrument has considerable advantages over SeaWiFS, This is particularly important given the complexity of the MODIS, and VIIRS, given its comparatively high spatial atmospheres over the coastal ocean and inland waters. resolution and many more spectral bands. No U.S. instru- ment will have MERIS capabilities for the foreseeable future. COCTS-CZI Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) COCTS-CZI/HY-1B CNSA (China) 2007 1,400/500 250/1100 10/4 402-12,500/433-885 With the exception of the general specifications in the table above, the committee did not obtain additional infor- mation on the status or performance of the Chinese Ocean Colour and Temperature Scanner/Coastal Zone Imager (COCTS-CZI). OCM-2 Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) OCM-2/Oceansat-2 ISRO (India) 2009 1,420 360/4,000 9 400-900 Sensor Description: radiance in the shorter wavelengths due to improved atmo- spheric corrections. The instrument was designed to provide OCM-2 was successfully launched in 2009 on board continuity with the OCM instrument. ISRO’s OCEANSAT-2 spacecraft. OCM-2 has the same The OCM-2 sensor has a swath of 1,420 km and similar design and specifications as OCM with the exception of a bands to OCM, with two changes: The 765 nm channel has shift in spectral bands 6 and 7 (Chauhan and Navalgund, been moved to 740 nm to avoid O2 absorption, and the 670 2009). The original 670 nm band (band 6) has shifted to nm channel has been replaced by a 620-nm channel for better 620 nm; the 765 nm band (band 7) has shifted to 740 nm to quantification of suspended sediments. Oceansat-2 has two avoid oxygen absorption. These improvements are expected modes of operation: Local Area Coverage (LAC) with 360- to provide greater accuracy of the normalized water-leaving
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83 APPENDIX A m real time transmission, and Global Area Coverage (GAC) of 4-km GAC data products on the Internet after the cal/val with 4-km onboard recording and playback. GAC data phase of the mission. A Letter of Intent with NASA/NOAA coverage is between ± 75o latitude covering the full globe in for OCEANSAT-2 data sharing was signed last year. eight days. The OCM-2 instrument is currently providing excellent datasets. The instrument has a tilting mechanism Data Availability: and the tilt is changed twice per year depending on seasonal- Open access7 users will be provided with Level 1-B ity, providing minimum sun glint over Indian waters. basic radiance products (atmospherically corrected), which can be displayed using SeaDAS. Level 2 products will con- Calibration: sist of chlorophyll-a concentration, Total Suspended Matter OCM-2 includes a solar and lunar calibration (lunar look (TSM), diffuse attenuation coefficients (Kd-490 nm), and once every six months) to assess sensor degradation.6 A per- Aerosol Optical Depth (AOD) at 865 nm and Level 3 (weekly manent cal/val site has been set up in the Lakashadweep Sea, and monthly averages generated on trial basis). Level 1 and 2 and data from an optical buoy are being used for vicarious data are available at a nominal cost directly from the National calibration of OCM-2 data. Extensive ship campaigns will Remote Sensing Centre (NRSC). also be organized for validation of geophysical data products. Level 3 products will consist of weekly, monthly, and The NRSA Data Center (NDC) will carry out dissemination yearly binned products (4 km). An OC-4-type algorithm has been developed for OCM-2 using bio-optical archived data collected in the Arabian Sea as well as data from NOMAD. 6 See http://www.ioccg.org/sensors/Navalgund_OCM-2.pdf; accessed October 22, 2010. 7 http://www.ioccg.org/sensors/Navalgund_OCM-2.pdf; accessed Oc- tober 22, 2010. Current Sensors in Geostationary Orbit Korean COMS-1 GOCI Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) GOCI/COMS KARI/KORDI 2010 2,500 500 8 400-865 (S. Korea) Earth (2) The Korea Aerospace Research Institute (KARI) devel- Earth oped and launched a GEO ocean color imager (GOCI) on Sensors (IRES) June 26, 2010, that is spectrally similar to the Sea-viewing GOCI Payload Wide Field-of-view Sensor (SeaWiFS). GOCI offers 360-m nadir ground sample distance (GSD; close to the CWI 300 MI m requirement) with sensor-provided pointing knowledge Payload of 10 mrad, corresponding to 360-m nadir pointing uncer- tainty (Faure et al., 2007). While the system (Figure A.1) is located for Asian seaboard imaging and therefore does not provide western Contiguous United States (CONUS) coastal imagery, it should allow sub-diurnal GEO coastal marine data-efficacy verification. KARI’s Communication and Ocean Monitoring Satellite (COMS) on which GOCI is mounted provides telecommuni- cations as well as GOCI data from a relatively small (2,300 kg) GEO spacecraft. This is less than the mass of larger (3,200 kg) commercial GEO communications satellites, yet carries the GOCI instrument that has 78-kg mass, 100-W A-1.eps power, 1.4 × 0.8 × 0.8 m dimensions (x, y, z; z = nadir), with 2 bitmaps FIGURE A.1 South Korean COMS-1 satellite with geostationary data rate dependent on custom-selected GOCI integration ocean color imager (GOCI) and the Asian seaboard viewing area. time per spectral band (Faure et al., 2007). SOURCE: Faure et al., 2007; used with permission from Astrium.
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84 APPENDIX A TABLE A.1 GOCI Spectral Capability. Central Wavelength SeaWIFS GOCT (nm) (bandwidth, nm) (bandwidth, nm) Primary Use 412 1(20) 1(20) Yellow substance and turbidity 443 2(20) 2(20) Chlorophyll absorption maximum 490 3(20) 3(20) Chlorophyll and other pigments absorption, K(490) 510 4(20) Chlorophyll absorption 555 5(20) 4(20) Suspended sediment 660 5(20) Fluorescence base 1, chlorophyll, suspended sediment 670 6(20) Atmospheric correction 680 6(10) Fluorescence signal, atmospheric correction 745 7(20) Atmospheric correction, fluorescence base 2 765 7(40) Atmospheric correction, aerosol radiance 865 8(40) 8(40) Aerosol optical thickness, vegetation, water vapor reference over the ocean The GOCI spectral capability (Table A.1) is modest, that even GOCI-like data, if located over CONUS, would with a filter wheel to select one of eight SeaWiFS-like spec- provide coastal data to partially close the existing ocean color tral bands at a time. Nevertheless, the GOCI provides a case data gap. Therefore, were there a low-cost means (compared study of the benefits of GEO vs. LEO ocean color sensing to the estimated cost of a GOES-R satellite, for example) via comparison of GOCI MODIS/SeaWiFS ocean color data. to place such a system in GEO, perhaps NOAA and NASA The committee believes it likely that NASA will conclude would consider it. Future Sensors in Polar Orbit VIIRS on NPP and JPSS 1 & 2 Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) VIIRS/NPP NOAA (USA) 2011 3,000 370/740 22 402-11,800 VIIRS/JPSS 1&2 NOAA (USA) After 2015 3,000 370/740 22 402-11,800 Sensor Description: Calibration: The Visible Infrared Imager Radiometer Suite (VIIRS) A single solar diffuser and four lunar calibration looks is a multi-spectral scanning radiometer scheduled to launch per year if no orbital maneuvers are permitted. in 2011. VIIRS was designed to provide global observations Initial calibration will utilize matches with MODIS- of land, ocean, and atmosphere parameters at high temporal Aqua. If resources can be mobilized to fund MOBY, MOBY resolution (~ daily). It consists of a multi-spectral scanning water-leaving radiances will be incorporated as part of the radiometer (with 22 bands between 400 and 1,200 nm) with vicarious calibration. The calibration for VIIRS on JPSS is a swath width of 3,000 km. likely to model the calibration of VIIRS on NPP, although the details regarding lunar maneuvers and a MOBY-like approach to vicarious calibration has to be determined.
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85 APPENDIX A Data Availability: ments (>15 years) that require the deployment of several satellites for each mission. NOAA CLASS facility; open availability. The first Sentinel-3 should be launched in 2013 (Sentinel 3A), and the second one (3B) in 2017. The OLCI is mostly Applications: based on the MERIS heritage but with 21 spectral channels instead of 15 and a fixed 12-degree across-track tilt that aims Water-leaving radiance and chlorophyll. to minimize sun glint (1,300-km swath). One satellite can obtain global coverage within four days; two satellites can OLCI Instrument on the Sentinel-3 platform do so within two days. The same principles previously used for MERIS radio- ESA is currently developing three satellite systems metric and spectral calibration are used for Sentinel-3/OLCI, that form part of the Space Component of the European ensuring a high level of radiometric accuracy and stability. GMES (Global Monitoring for Environment and Security) The product suite includes all products already provided program. The Sentinel-3, one of these missions, carries the by MERIS plus some advanced products, such as inherent wide-swath, medium resolution (300 m at nadir) visible optical properties. and near-infrared “Ocean Land Colour Instrument” (OLCI) The Sentinel-3 data policy is dictated by the GMES spectroradiometer. data policy, i.e., free and open access to all data. The OLCI The Sentinel-3 mission is meant to be operational, so it operational ground segment should be operated by EUMET- has stringent revisit, coverage, and mission life cycle require- SAT. Other entities will operate the decentralized “thematic” ground segment. S-GLI Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) S-GLI/GCOM-C JAXA (Japan) 2014 1,150-1,400 250/1,000 19 375-12,500 Sensor Description: The target for data accuracy of SGLI products is at the same level for GLI products (Murakami et al., 2006). The Second-Generation Global Imager (S-GLI) will be flown as part of the Global Change Observation Mission for Climate research (GCOM-C) mission. This sensor is a Data Availability: follow-on to the GLI, a multi-spectral radiometer with 19 Data products expected to be available online.9 wavebands ranging from 375 to 12,500 nm. The 250-m spa- tial resolution aims at improving coastal ocean and aerosol observations. Applications: The S-GLI observations aim to improve our under- Calibration: standing of climate change mechanisms through long-term monitoring of aerosols, ocean color, derived phytoplankton Onboard calibrations will include a solar diffuser, inter- and clouds, as well as vegetation and temperatures. nal lamp, lunar look by pitch maneuvers (for visible chan- nels) and lunar through deep space window (for short wave channels), and dark current.8 9 See http://www.eorc.jaxa.jp. 8 See http://www.ioccg.org/sensors/SGLI_mission_design_201002.pdf; accessed October 25, 2010.
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86 APPENDIX A COCTS-CZI Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) COCTS-CZI/HY-1C/D CNSA (China) 2014 2,900/1,000 250/1,100 10/10 402-12,500/433-885 COCTS-CZI/HY-1E/F CNSA (China) 2017 2,900/1,000 250/1,100 10/4 402-12,500/433-885 With the exception of the general specifications in the table above, the committee did not obtain additional infor- mation on the status or performance of the Chinese Ocean Colour and Temperature Scanner/Coastal Zone Imager (COCTS-CZI). PACE and ACE Sensor/Satellite Agency Launch Date Swath Resolution Bands Spectral Coverage (nm) PACE NASA (USA) >2019 116.6 degree 1 km 26 spectral bands 350-2,135 nm (5-nm resolution 350-775 nm) Sensor Description: Data Availability: The Pre-Aerosol-Clouds-Ecosystem (PACE) and The data likely will be freely and openly available. Aerosol-Cloud-Ecosystems (ACE) mission aim to advance research in ocean biology and biogeochemical cycles. Applications: The products derived from these sensors will be applied Calibration: to research on the carbon cycle, marine ecosystem, phyto- The need for direct lunar calibration, a vicarious cali- plankton physiology, near-shore and estuarine processes, and bration site, and global data for product validation are listed on physical-biological interactions. among the mission requirements.