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Summary T he ocean hosts a fundamental component of Earth’s Resolution Imaging Spectroradiometer (MODIS, on Terra in biosphere. Marine organisms play a pivotal role in 1999 and on Aqua in 2002) is at risk. The demise of SeaWiFS the cycling of life’s building blocks such as nitrogen, in December 2010 has accentuated this risk. MODIS on carbon, oxygen, silica, and sulfur. About half of the global Aqua is currently the only U.S. sensor in orbit that meets all requirements (see below) for sustaining the climate-quality1 primary production—the process by which CO2 is taken up by plants and converted to new organic matter by photosyn- ocean color time-series and products. However, this sensor thesis—occurs in the ocean. Most of the primary producers is also many years beyond its design life. Furthermore, it is in the ocean comprise microscopic plants and some bacteria; no longer possible to rectify problems with the Aqua sensor these photosynthetic organisms (phytoplankton) form the degradation that were addressed through comparisons with base of the ocean’s food web. Scientists are exploring how SeaWiFS in the past few years. Therefore, it is uncertain future climate change and sea surface warming might impact how much longer data from U.S. sensors will be available to the overall abundance of phytoplankton. A long-term change support climate research. Although the European Medium- in phytoplankton biomass would have major implications Resolution Imaging Spectrometer (MERIS) meets all the for the ocean’s ability to take up atmospheric CO2 and sup- requirements of a successful mission, it is also beyond its port current rates of fish production. Therefore, sustaining a design life. Because of the many uncertainties surrounding global record of the abundance of phytoplankton and their the next U.S. satellite mission (more specifically the Visible contribution to global primary productivity is required to Infrared Imager Radiometer Suite [VIIRS] sensor scheduled assess the overall health of the ocean, which is currently to launch fall 2011); data acquired through the VIIRS mis- threatened by multiple stresses such as increased tempera- sion threaten to be of insufficient quality to continue the ture and ocean acidification (both due to anthropogenic CO2 climate-quality time-series. emissions), marine pollution, and overfishing. Even if fully successful, the VIIRS sensor’s capabilities Because the ocean covers roughly 70 percent of Earth’s are too limited to explore the full potential of ocean color surface, ships alone cannot collect observations rapidly remote sensing. Thus, the U.S. research community is looking enough to provide a global synoptic view of phytoplankton to National Aeronautics and Space Administration (NASA) abundance. Only since the launch of the first ocean color to provide ocean color sensors with advanced capabilities to satellite (the Coastal Zone Color Scanner [CZCS] in 1978) support new applications and for significant improvements to has it been possible to obtain a global view of the ocean’s current research products beyond what is possible with data phytoplankton biomass in the form of chlorophyll. These from SeaWiFS and MODIS or will be possible from VIIRS. observations led to improved calculations of global ocean However, the Pre-Aerosol-Clouds-Ecosystem (PACE)—the primary production, as well as better understanding of the first of NASA’s planned three missions that would advance processes affecting how biomass and productivity change the capabilities for basic ocean color research—is not sched- within the ocean basins at daily to interannual time scales. uled to launch before 2019. Without the ability to sustain high-quality ocean color measurements or to launch next generation sensors with new THE OCEAN COLOR TIME-SERIES IS AT RISK Currently, the continuous ocean color data record col- 1 Climate-quality observations are a time-series of measurements of suf - lected by satellites since the launch of the Sea-viewing Wide ficient length, consistency, and continuity to assess climate variability and Field-of-view Sensor (SeaWiFS, in 1997) and the Moderate change (following NRC, 2004b). 1

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2 SUSTAINED OCEAN COLOR RESEARCH AND OPERATIONS capabilities, many important research and operational uses properties, measurements need to meet stringent accuracy are compromised, including the capability to detect impacts requirements. Achieving this high accuracy is a challenge, of climate change on primary productivity. Therefore, it is and based on a review of lessons learned from the SeaWiFS/ imperative to maintain and improve the capability of satel- MODIS era, requires the following steps to sustain current lite ocean color missions at the accuracy level required to capabilities: understand changes to ocean ecosystems that potentially affect living marine resources and the ocean carbon cycle, 1. The sensor needs to be well characterized and cali- and to meet other operational and research needs. Given brated prior to launch. the importance of maintaining the data stream, the National 2. Sensor characteristics, such as band-set and signal- Oceanic and Atmospheric Administration (NOAA), NASA, to-noise, need to be equivalent to the combined best attributes the National Science Foundation (NSF), and the Office of from SeaWiFS and MODIS. 3. Post-launch vicarious calibration3 using a Marine Naval Research (ONR) asked the National Research Council to convene an ad hoc study committee to review the mini- Optical Buoy (MOBY)-like approach with in situ measure- mum requirements to sustain global ocean color radiance ments that meet stringent standards is required to set the gain measurements for research and operational applications and factors of the sensor. to identify options to minimize the risk of a data gap (see 4. The sensor stability and the rate of degradation need to be monitored using monthly lunar looks.4 Box S.1 for the full statement of task). Because the ability to sustain current capabilities is at risk, the report focuses on 5. At least six months of sensor overlap are needed to minimum requirements to sustain ocean color observations transfer calibrations between space sensors and to produce of a quality equivalent to the data collected from SeaWiFS. continuous climate data records. Meeting these requirements will mitigate the risk of a gap in 6. The mission needs to support on-going develop- the ocean color climate data record but will be insufficient to ment and validation of atmospheric correction, bio-optical explore the full potential of ocean color research and will fall algorithms, and ocean color products. short of meeting all the needs of the ocean color research and 7. Periodic data reprocessing is required during the operational community. To meet all these needs, a constel- mission. lation of multiple sensor types2 in polar and geostationary 8. A system needs to be in place that can archive, orbits will be required. Note that satellite requirements for make freely available, and distribute rapidly and efficiently all raw,5 meta- and processed data products to the broad research leading to the generation of novel products would vary depending on the question addressed and are difficult national and international user community. to generalize. 9. Active research programs need to accompany the mission to improve algorithms and products. 10. Documentation of all mission-related aspects needs THE REQUIREMENTS TO OBTAIN HIGH-QUALITY to be accessible to the user community. GLOBAL OCEAN COLOR DATA Satellite ocean color sensors measure radiance at differ- Meeting these requirements would contribute to sus- ent wavelengths that originate from sunlight and are back- taining the climate-quality global ocean color record for the scattered from the ocean and from the atmosphere. Deriving open ocean. However, further enhancements to sensors and the small ocean component from the total radiance measured missions, such as higher spectral and spatial resolution, will by satellite sensors is a complex, multi-step process. Each be required to meet the research and operational needs for step is critical and needs to be optimized to arrive at accurate imaging coastal waters and for obtaining information about and stable measurements. Using a set of algorithms (starting the vertical distribution of biomass or particle load. High with removal of the contribution from the atmosphere, which frequency sampling (e.g., imagery every 30 minutes for a is most of the signal), radiance at the top of the atmosphere is fixed ocean area), such as can be obtained from geostation- converted to water-leaving radiance (Lw) and then to desired ary orbit, are desirable enhancements for applications such properties such as phytoplankton abundance and primary as ecosystem and fisheries management, as well as naval productivity. To detect long-term climactic trends from these applications. 3 Vicarious calibration refers to techniques that use natural or artificial 2 Type 1: Polar orbiting sensors with relatively low spatial resolution (1 sites on the surface of Earth and models for atmospheric radiative transfer km) with 8 (or many more) wave bands. to provide post-launch absolute calibration of sensors. 4 Monthly lunar looks refers to the spacecraft maneuver that looks at the Type 2: Polar orbiting sensors with medium spatial resolution (250-300 m) and more bands to provide a global synoptic view at the same time as surface of the moon once a month as a reference standard to determine how allowing for better performance in coastal waters. stable the sensor’s detectors are. The information from the lunar looks is then Type 3: Hyper-spectral sensors with high spatial resolution (~30m) in used for determining temporal changes in sensor calibration. 5 R aw data is defined as data in engineering units to which new polar orbit. Type 4: Hyper- or multi-spectral sensors with high spatial resolution in calibration factors can be applied to generate radiance values at the top of geostationary orbit. the atmosphere.

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3 SUMMARY Box S.1 Statement of Task Continuity of satellite ocean color data and associated climate research products are presently at significant risk for the U.S. ocean color community. Temporal, radiometric, spectral, and geometric performance of future global ocean color observing systems must be considered in the context of the full range of research and operational/application user needs. This study aims to identify the ocean color data needs for a broad range of end users, develop a consensus for the minimum requirements, and outline options to meet these needs on a sustained basis. An ad hoc committee will assess lessons learned in global ocean color remote sensing from the SeaWiFS/MODIS era to guide planning for acquisition of future global ocean color radiance data to support U.S. research and operational needs. In particular, the committee will assess the sensor and system requirements necessary to produce high-quality global ocean color climate data records that are consistent with those from SeaWiFS/MODIS. The committee will also review the operational and research objectives, such as described in the Ocean Research Priorities Plan and Implementation Strategy, for the next generation of global ocean color satellite sensors and provide guidance on how to ensure both operational and research goals of the oceanographic community are met. In particular the study will address the following: 1. Identify research and operational needs, and the associated global ocean color sensor and system high-level require- ments for a sustained, systematic capability to observe ocean color radiance (OCR) from space; 2. Review the capability, to the extent possible based on available information, of current and planned national and international sensors in meeting these requirements (including but not limited to: VIIRS on NPP and subsequent JPSS spacecrafts; MERIS on ENVISAT and subsequent sensors on ESA’s Sentinel-3; S-GLI on JAXA’s GCOM-C; OCM-2 on ISRO’s Oceansat-2; COCTS on SOA’s HY-1; and MERSI on CMA’s FY-3); 3. Identify and assess the observational gaps and options for filling these gaps between the current and planned sensor capabilities and timelines; define the minimum observational requirements for future ocean color sensors based on future oceanographic research and operational needs across a spectrum of scales from basin-scale synoptic to local process study, such as expected system launch dates, lifetimes, and data accessibility; 4. Identify and describe requirements for a sustained, rigorous on-board and vicarious calibration and data validation program, which incorporates a mix of measurement platforms (e.g., satellites, aircraft, and in situ platforms such as ships and buoys) using a layered approach through an assessment of needs for multiple data user communities; and 5. Identify minimum requirements for a sustained, long-term global ocean color program within the United States for the maintenance and improvement of associated ocean biological, ecological, and biogeochemical records, which ensures continuity and overlap among sensors, including plans for sustained rigorous on-orbit sensor inter-calibration and data validation; algorithm development and evaluation; data processing, re-processing, distribution, and archiving; as well as recommended funding levels for research and operational use of the data. The review will also evaluate the minimum observational research requirements in the context of relevant missions outlined in previous NRC reports, such as the NRC “Decadal Survey” of Earth Science and Applications from Space. The committee will build on the Advance Plan developed by NASA’s Ocean Biology and Biogeochemistry program and comment on future ocean color remote sensing support of oceanographic research goals that have evolved since the publication of that report. Also included in the review will be an evaluation of ongoing national and international planning efforts related to ocean color measurements from geostationary platforms. ASSESSMENT OF CURRENT AND FUTURE SENSORS comes at a very critical time. Unless there is a successful IN MEETING THESE REQUIREMENTS transition from European Space Agency’s (ESA) MERIS to ESA’s Ocean Land Colour Instrument (OLCI) sensor, and As Figure S.1 indicates, all current sensors except for data from OCLI are available immediately, the success and Ocean Colour Monitor on-board Oceansat-2 (OCM-2) are the continuity of the global ocean color time-series will be beyond their design life. The recent demise of SeaWiFS is dependent on the success of the VIIRS mission, because also putting into question the future of the MODIS sensors OCM-2 does not collect global data. because their recent rapid degradation resulted in a reliance The research community has long questioned the ability on SeaWiFS data to calibrate the MODIS data. Without this of VIIRS to deliver high-quality data because of a manu- calibration, it is unclear how long MODIS data can be made facturing error in one of its optical components. Since this available at the necessary accuracy. MERIS is a high-quality issue has been raised, the sensor has been mounted onto its mission but also beyond its design life. launch vehicle and undergone additional testing and char- Therefore, the launch of VIIRS planned for fall 2011

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4 SUSTAINED OCEAN COLOR RESEARCH AND OPERATIONS ??? ??? ??? ??? 10-year ??? Data Gap ??? ??? ??? Data Gap? FIGURE S.1 The launch sequence of past, current, and planned ocean 4-1).eps in polar orbit are displayed. The sensors still operational S.1 (and color sensors are shown with a one-sided arrow; the hatched area indicates when a sensor is beyond its design life. The gray shaded background indicates bitmap with added vector elements a data gap in the past and a potential data gap if MODIS sensors and MERIS cease today. The question marks are used to indicate sensors that either do not yet meet the minimum requirements or are vulnerable to changes in funding allocation. Future sensors are shown having either a five- or seven-year lifetime, according to their individual specifications. CZCS: Coastal Zone Color Scanner; OCTS: Ocean Color and Temperature Scanner; SeaWiFS: Sea-viewing Wide Field-of-view Sensor; OCM/OCM-2: Ocean Colour Monitor; MODIS-Terra/MODIS- Aqua: Moderate Resolution Imaging Spectroradiometer on Terra/Aqua, respectively; MERIS: Medium Resolution Imaging Spectrometer; GLI: Global Imager; VIIRS: Visible Infrared Imager Radiometer Suite; OLCI: Ocean Land Colour Instrument onboard Sentinel-3; PACE: Pre-Aerosol-Clouds-Ecosystem; GCOM-C: Global Change Observation Mission for Climate Research; JPSS: Joint Polar Satellite System. SOURCE: Based on data from http://www.ioccg.org/sensors_ioccg.html. 1. implement spacecraft maneuvers as part of the acterization. The most recent tests have resulted in a more mission, including monthly lunar looks using the Earth- optimistic assessment about its performance, and a software viewing port to quantify sensor stability; solution to overcome part of the optical hardware issue has 2. form a calibration team with the responsibility and been proposed. authority to interact with those generating Level 16 prod- However, based on the committee’s assessment of the ucts, as well as with the mission personnel responsible for overall planning and budgeting, it is currently unlikely that this mission will provide data of sufficient quality to con- tinue the ocean color climate data record. This conclusion reflects inadequacies in the current overall mission design 6There are five different levels of processing of satellite data: and provisions to address all the key requirements of a suc- Level 0: Raw data as measured directly from the spacecraft in engineering units (e.g., volts or digital counts). cessful ocean color mission (see above for 10 requirements). Level 1: Level 0 data converted to radiance at the top of the atmosphere In particular, NOAA has not developed a capacity to process using pre-launch sensor calibration and characterization information and reprocess the data such as is available at NASA. adjusted during the life of the mission by vicarious calibration and stability monitoring. Conclusion: VIIRS/NPP has the potential to continue the Level 2: Data generated from Level 1 data following atmospheric correction that are in the same satellite viewing coordinates as Level 1 data. high-quality ocean color time-series only if NOAA takes Level 3: Products that have been mapped to a known cartographic ALL of the following actions: projection or placed on a two-dimensional grid at known spatial resolution. Level 4: Results derived from a combination of satellite data and ancillary information, such as ecosystem model output.

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5 SUMMARY the sensor, to provide the analyses needed to assess trends 1. A U.S. program is established to coordinate access in sensor performance and to evaluate anomalies; to data from non-U.S. sensors, including full access to pre- 3. implement a vicarious calibration process and team launch characterization information and timely access to using a MOBY-like approach; post-launch Level 1 or Level 0 data, and direct downlink 4. implement a process to engage experts in the field for real-time access; and of ocean color research to revisit standard algorithms and 2. This program includes sufficient personnel and products, including those for atmospheric correction, to financing to collect independent calibration and valida- ensure consistency with those of heritage instruments and tion data, assess algorithms and develop new algorithms as for implementing improvements; required, produce and distribute data products required by 5. form a data product team to work closely with the U.S. users, support interactions among U.S. research and calibration team to implement vicarious and lunar calibra- operational users in government, academia and the private tions, oversee validation efforts, and provide oversight of sector, and has the capability to reprocess data from U.S. reprocessing; and missions (e.g., MODIS, SeaWiFS) as well as the non-U.S. 6. provide the capability to reprocess the mission data sensors to establish a continuous time-series of calibrated multiple times to incorporate improvements in calibration, data. correct for sensor drift, generate new and improved prod- ucts, and for other essential reasons. The committee finds that non-U.S. sensors can be viewed as a source of data to complement and enhance Conclusion: If these steps are not implemented, the United U.S. missions. For example, merging calibrated data from States will lose its capability to sustain the current time- multiple sensors, particularly if the sensors have different series of high-quality ocean color measurements from U.S. equatorial crossing times, can provide much more complete operated sensors in the near future, because the only cur- global coverage than is possible from a single sensor. Mean rent viable U.S. sensor in space (MODIS-Aqua) is beyond coverage from a single sensor averages about 15 percent of its design life. the global ocean per day, owing to cloud cover and limita- tions imposed by swath width and orbit characteristics. Daily Regardless of how well VIIRS performs, it has only a coverage can be increased by merging data from multiple very limited number of ocean color spectral bands and thus sensors, if they are in complementary orbits. Furthermore, cannot provide the data required by the research community sensors such as MERIS, OLCI, and OCM-2 have much for advanced applications. Under ideal conditions of inter- better capabilities—including higher spatial and spectral national cooperation, data from U.S. and non-U.S. sensors resolution—for imaging coastal waters than current U.S. planned for the future could be made readily available to sensors or VIIRS. Routine access to the data from these non- meet the many needs for research and operations, but ideal U.S. sensors, particularly MERIS and OLCI, is essential to conditions are difficult to negotiate for many complicated advance the research and operational uses of ocean color data reasons. The European MERIS mission is currently pro- for U.S. coastal applications. OCM-2 has potential but is not viding high-quality global data, albeit with somewhat less currently operated for global observations. frequent global coverage owing to its narrower swath as Finally, non-U.S. space agencies are taking some of the compared to the U.S. missions. The European Space Agency development risk for new approaches to ocean color data (ESA) expects MERIS will continue to operate until its collection. For example, South Korea in 2010 became the follow-on sensor (OLCI) is launched on ESA’s Sentinel-3 first country to put an ocean color imager into geostationary platforms in 2013. ESA, NASA and NOAA have ongoing orbit (viewing the East China Sea), and thus will help the discussions about full exchange of MERIS mission data, international user community understand the potential of this including raw satellite data and calibration data. The Indian approach, including the capability to view the same ocean space agency launched the OCM-2 sensor in 2009. OCM-2 area about every 30 minutes during daylight hours. has excellent technical specifications, but to date, data access is very limited. Furthermore, OCM-2 is not a global mission; MINIMIZING THE RISK OF A DATA GAP its data collection priority focuses on the Indian Ocean. The Japanese space agency is planning an advanced ocean The risk of a data gap in the U.S. ocean color time-series color sensor, Second-Generation Global Imager (S-GLI), for is very real and imminent because MODIS is not likely launch in 2014 that has high potential based on its technical to deliver high-quality data for much longer. Many issues specifications. remain unresolved regarding the VIIRS missions, and the next U.S. ocean color mission, NASA’s Pre-Aerosol-Clouds- Conclusion: Under the following conditions non-U.S. sen- Ecosystem (PACE) mission, will not launch before 2019. sors can be viable options in replacing or augmenting data: To minimize this risk, the principal recommendation of the committee is:

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6 SUSTAINED OCEAN COLOR RESEARCH AND OPERATIONS Recommendation: NOAA should take all the actions out- Recommendation: To move toward a partnership, NASA lined above to resolve remaining issues with the VIIRS/ and NOAA should form a working group to determine NPP. In addition, NOAA needs to fix the hardware prob- the most effective way to satisfy the requirements of each lems on the subsequent VIIRS sensors and ensure all the agency for ocean color products from VIIRS and to con- above actions are incorporated into the mission planning sider how to produce, archive, and distribute products of for the subsequent VIIRS launches on JPSS-1 and JPSS-2. shared interest, such as climate data records, that are based Taking these steps is necessary to generate a high-quality on data from all ocean color missions. This group should dataset, because VIIRS is the only opportunity for a U.S. comprise representatives from both agencies and include a ocean color mission until the launch of NASA’s PACE mis- broad range of stakeholders from the ocean color research sion, currently scheduled for launch no earlier than 2019. and applications community. In addition, if MERIS ceases operation before Sentinel-3A is launched in 2013, VIIRS/NPP would be the only global Based on its review of previous ocean color missions, ocean color sensor in polar orbit. the committee concludes that a long-term national program to support ocean color remote sensing involves multiple To develop quality ocean color products requires highly agencies—NOAA and NASA in particular, with input from specialized skill and expertise. Currently, the NASA Ocean the academic research community, and continuous funding Biology Processing Group (OBPG) at Goddard Space Flight that goes beyond the lifetime of any particular satellite mis- Center (GSFC) is internationally recognized as a leader in sion. Such a mechanism is required to ensure that: producing well-calibrated, high-quality ocean color data products from multiple satellite sensors. NOAA currently 1. continuity is achieved and maintained between U.S. lacks the demonstrated capacity to readily produce high- and non-U.S. satellite missions; quality ocean color products and provide the comprehen- 2. lessons learned from previous missions are incorpo- sive services currently available from the OBPG, although rated into the planning for future missions; NOAA is in the process of building its capacity. For example, 3. mission planning and implementation are timed although NOAA’s National Climate Data Center (NCDC) appropriately to ensure continuity between satellite missions; plans to archive a climate-level7 radiance data record, it is 4. capability for data processing and reprocessing of unclear how NOAA can generate the products or make them U.S. and non-U.S. missions is maintained; and easily accessible to U.S. and foreign scientists. 5. planning for transition from research to operation Both NASA and NOAA support ocean color applica- occurs early for each mission and is implemented seam- tions, with NASA focused primarily on research and devel- lessly via cooperation and interaction between government, opment and NOAA focused on operational uses. Because academic, and private-sector scientists. both agencies have a strong interest in climate and climate Recommendation: To sustain current capabilities, NOAA impacts, they share a common interest in climate data and NASA should identify long-term mechanisms that can: records.If NOAA builds its own data processing/reprocess- ing group, two independent federal groups will then be devel- oping ocean color products and climate data records. While • provide stable funding for a MOBY-like approach for this can be justified given the distinct missions of NOAA and vicarious calibration; NASA, it can also raise problems when discrepancies appear • maintain the unique ocean color expertise currently in the data records. Moreover, the committee anticipates available at NASA’s OBPG over the long term and make it major challenges to generating high-quality products from available to all ocean color missions; the VIIRS/NPP data, which call for involving the expertise • nurture relations between NASA and NOAA scien- currently only available at NASA’s OBPG. For these reasons, tists so that both agencies meet their needs for ocean color the committee concludes the following: data in the most cost-effective manner and without needless duplication; Conclusion: NOAA would greatly benefit from initiating • establish and maintain validation programs, and and pursuing discussions with NASA for an ocean color maintain and distribute the data over the long term; partnership that would build on lessons learned from Sea- • provide the planning and build the will for continuity WiFS and MODIS, in particular.8 in the satellite missions over the long term; and • sustain the viability of the scientific base by support- ing research and training. 7Climate-level means repackaged data to look like a MODIS granule The committee envisions that such a mechanism could and all metadata repackaged accordingly to ease the reprocessing of the Level 0 data. be a U.S. working group modeled after the International 8 Consistent with the conclusions and recommendations of “Assessment Ocean Colour Coordinating Group (IOCCG). The establish- of Impediments to Interagency Collaboration on Space and Earth Science ment of a working group with representation from all the Missions” (NRC, 2010).

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7 SUMMARY sions to sustain optimal ocean color radiance data for all interested federal agencies, from U.S. academic institutions applications. and the private sector could provide the necessary long-range planning to meet the needs of U.S. users, provide external Recommendation: NOAA’s National Environmental Satel- advice to the individual missions, interact with foreign part- lite, Data, and Information Service and NASA’s Science ners, and develop consensus views on data needs and sensor Mission Directorate should increase efforts to quickly requirements. establish lasting, long-term data exchange policies, because U.S. users are increasingly dependent on ocean color data CONCLUSION from non-U.S. sensors. The diverse applications of, and future enhancements to, ocean color observations will require a mix of ocean color The IOCCG presents an effective body through which satellites in polar and geostationary orbit with advanced NASA and NOAA can engage with foreign space agencies c apabilities. Although the three missions described in and develop a long-term vision for meeting the research and NASA’s Decadal Survey (Aerosol-Cloud-Ecosystem/Pre- operational needs for ocean color products. Through the Aerosol-Cloud-Ecosystem, Geostationary Coastal and Air IOCCG, space agencies can identify options for collabora - Pollution Events [GEOCAPE], and Hyperspectral Infrared tions and approaches mutually beneficial to all interested Imager [HyspIRI]) will potentially provide many advanced parties. The group has been active in communicating user capabilities, meeting all user needs within the next decade needs and is working with the Committee on Earth Obser- will likely surpass the capability of a single space agency vation Satellites (CEOS) to develop plans for the Ocean Colour Radiometry Virtual Constellation9 (OCR-VC). In or nation. the long term, international partnerships will be needed to Conclusion: U.S. scientists and operational users of satel- sustain the climate-quality global ocean color time-series, lite ocean color data will need to rely on multiple sources, and at the same time, to advance ocean color capabilities including sensors operated by non-U.S. space agencies, and research. because the United States does not have approved mis- 9 A virtual constellation is a set of space and ground segment capabilities operating together in a coordinated manner; in effect, a virtual system that overlaps in coverage in order to meet a combined and common set of Earth Observation requirements. The individual satellites and ground segments can belong to a single or multiple owners.