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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report 2 Summary of the Workshop Sessions The workshop’s breakout sessions were designed to have participants consider the impact of changes to the NPOESS and GOES-R programs from many different perspectives. On day 1 of the workshop, participants considered impacts in terms of their effects on the measurement of essential climate variables (ECVs), as specified by the GCOS Implementation Plan.1 On day 2, impacts were considered in terms of the specific sensors that constituted the original programs’ baselines. The panel recognized that there would be overlap in these discussions, but thought it useful for participants to consider the broad issues of ECV measurement and development of climate data records (CDRs) apart from specific concerns about NPOESS sensors. Day 3 breakout discussions were more loosely organized, to allow for broad discussion of cross-cutting issues, long-term considerations critical to the production of CDRs, and the advance of climate science in general. Indeed, a recurring theme expressed by many participants at the workshop was that ensuring the measurement(s) of a particular climate variable(s) was only a necessary first step toward enabling the creation of time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change, that is, to generate CDRs (see “Panel on Issues Related to CDR Development,” p. 39). WORKSHOP SUMMARY—DAY 1 The day 1 breakout groups were charged to consider, as a community, the various ECVs that might be affected by the Nunn-McCurdy NPOESS and GOES-R descopes. Participants considered each NPOESS-measured parameter, starting with ones in jeopardy of not meeting Integrated Operational Requirements Document (IORD) specifications, commenting on the relevance of the parameter to climate science and/or long-term climate records, the importance of maintaining the IORD-level value (and potential consequences if it is not met), and noting any additional considerations required to make the NPOESS program’s environmental data records (EDRs) more relevant to GCOS ECV climate parameters and to the climate community as a whole (e.g., additional instrument characterization, calibration, overlap requirements). Participants were also encouraged to suggest mitigation approaches where NPOESS current plans fall short of climate community needs, and to assess whether any of the missions recommended in the Earth science decadal survey2 might enable recovery of the NPOESS climate 1 The GCOS Implementation Plan (GCOS-107) is available at http://www.wmo.int/pages/prog/gcos/Publications/gcos-107.pdf. 2 NRC, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, The National Academies Press, Washington, D.C., 2007.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report measurements. Participant feedback on each of these areas was captured in real-time in a template,3 and a brief summary of the discussions is provided here. Consideration of NPOESS and GOES-R Priority Measurements for ECVs— Breakout Sessions Climate Data Records Related to Observations of the Atmosphere The atmosphere ECV breakout group was asked to consider 10 ECVs related to observations of the atmosphere: Earth radiation budget (including solar irradiance); aerosol properties; ozone; carbon dioxide, methane, and other greenhouse gases; cloud properties; precipitation; water vapor; surface wind speed and direction; upper-air wind; and upper-air temperature. Recognizing the linkages between the ECVs, the group organized itself into four subgroups: Radiation budget (Earth radiation budget, aerosol properties), Ozone and trace gases (ozone; carbon dioxide, methane, and other greenhouse gases), Clouds and precipitation and water vapor (cloud properties, precipitation, water vapor), and Winds and temperature (surface wind speed and direction, upper-air wind, upper-air temperature). A summary of the discussions is provided here, organized according to ECV. Earth Radiation Budget (Including Solar Irradiance) Persistent small climate changes are difficult to detect within the diurnal, regional, and seasonal variance of Earth’s reflected (shortwave) and emitted (longwave) energy—hence a continuous long-term (decades) record of Earth’s radiation budget (ERB) is needed to identify subtle long-term shifts related to climate change.4 With the demanifesting of TSIS and ERBS from NPOESS, ERB measurements will end with the last CERES on Aqua (or perhaps NPP, pending addition of CERES FM-5 onto NPP), the TIM record will end with Glory, and the SIM record with SORCE. Planned or proposed international missions and instruments of relevance include EarthCARE, ScaRAB on Megha-Tropiques, and GERB; however, in the view of breakout participants who commented on them, these international missions are insufficient to maintain the ECVs. The Earth science decadal survey recommended that NOAA add CERES to NPP and that NASA develop CLARREO, which would provide spectral ERB measurements. It was noted that ERBS (Earth radiation budget sensor) needs VIIRS cloud imagery, and so flight near NPOESS was desirable. SIM and TIM could be on separate spacecraft from ERBS since they are Sun pointing. Aerosol Properties Measurement of aerosol properties is needed to understand the global distribution of aerosols and their impact on Earth’s energy balance, clouds, and precipitation. Aerosol impacts remain a source of major uncertainty in climate prediction in the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (2007).5 Recent and ongoing missions and instruments providing aerosol information include TOMS (1979-), AVHRR (1979-), MODIS (1999-), MISR (1999-), POLDER (2002-), (A)ATSR (1991-), PARASOL (2006-), SCIAMACHY (2003-), CALIPSO (2006-), GLAS (2003-), OMI (2004-), and AIRS (2002-). International missions of relevance include EarthCARE, GCOM-C/SGLI, ADM/Aeolus, and ATLID. The upcoming NASA Glory mission will fly APS, which was originally intended to be followed by subsequent NPOESS flights of APS to provide a continuing data record. With the demanifesting of APS from NPOESS, some aerosol information will be obtained through 3 The filled-in templates are available at http://www7.nationalacademies.org/ssb/SSB_NPOESS2007_Presentations.html. 4 See, for example, NRC, Solar Influences on Global Change, National Academy Press, Washington, D.C., 1994. 5 Intergovernmental Panel on Climate Change, Climate Change 2007, IPCC Fourth Assessment Report, Cambridge University Press, Cambridge, U.K., 2008, available at http://www.ipcc.ch/ipccreports/assessments-reports.htm.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report VIIRS, OMPS, and CrIS/ATMS; however, these instruments will not provide polarimetry information. Workshop participants noted that the ACE mission, as described in the Earth science decadal survey, would provide significant advances. Attendees expressed a strong desire to move to a next-generation polarimeter rather than lock in to the technology of APS, as would have been required for accommodation on NPOESS. The 3D-Winds mission recommended in the decadal survey would provide aerosol heights, which would also contribute to measurement of the properties of this ECV. Ozone The ozone ECV is important to monitoring the long-term trends in surface ultraviolet (UV) radiation and recovery of the ozone layer. The ozone ECV is at risk due to the demanifesting of OMPS-Limb by the NPOESS program, although it has recently been restored to the NPP platform. After NPP, no ozone profile measurement is currently planned as part of NPOESS, which after the Nunn-McCurdy action carries only the OMPS-Nadir portion of the original suite. Ongoing missions and instruments of relevance to the ozone ECV include TOMS (1979-), SBUV (1979-), GOME (2006-), MIPAS (2003-), OMI (2003-), SCIAMACHY (2003-), TES (2005-), GOME-II (2006-), MLS (2004-), AIRS (2002-), and IASI (2006-). The decadal survey recommendation for GACM was considered relevant to the ozone ECV, although it was recommended for launch after 2016. In the breakout session, several participants noted that the NPOESS nadir ozone measurement (which is the only ozone measurement to be made by NPOESS) is more than adequately covered by GOME-II on MetOp and that ozone profile measurements would add more value than additional nadir measurements. Carbon Dioxide, Methane, and Other Greenhouse Gases Measurements of key greenhouse gases, including CO2 and CH4, are essential parts of a program to understand climate forcings and trends. Indeed, measurements are needed with sufficient quality to detect sources and sinks at regional scales. The NPOESS CrIS instrument will contribute to this ECV, and some breakout participants noted that its value would be increased if all the spectra were downlinked. Ongoing missions and instruments related to the greenhouse gases ECV include IRS (2002-), SCIAMACHY (2003-), MIPAS (2003-), HIRDLS (2004-), MLS (2004-), TES (2004-), GOME-II (2006-), and IASI (2006-). AIRS and IASI both currently produce midtroposphere CO2 data products, although both remain to be validated. NASA’s planned OCO mission (scheduled for launch late in 2008) and the JAXA GOSAT mission will also contribute to the CO2 measurement needs for this ECV. The decadal-survey-recommended ASCENDS mission is also of interest. Some workshop participants noted the desirability of a GIFTS- or HES-like instrument for geostationary measurements (with high temporal resolution) relevant to this ECV. Cloud Properties Ongoing missions and instruments of relevance to the cloud properties ECV include AVHRR/HIRS (1978-), (A)ATSR (1991-), MODIS (2000-), MISR (1999-), AIRS (2002-), SEVIRI (2003-), GOES (1994-), METSAT (2004-), MTSAT-1R (2005-), IASI (2006-), CloudSat (2006-), and CALIPSO (2006-). On NPOESS, contributions include VIIRS (which includes a day and a night imager) and CrIS/ATMS (and, prior to the Nunn-McCurdy action, APS). Planned missions/instruments of relevance include GLM and EarthCARE. The cloud properties ECV can be significantly advanced via the ACE mission recommended by the Earth science decadal survey, which would investigate aerosol-cloud interactions. Precipitation The water cycle plays a critical role in climate change. Precipitation measurements are key to understanding and predicting water vapor feedback, water supply, drought, severe storms, and floods. Ongoing missions and instruments of relevance to precipitation measurement include SSM/I (1987-), TMI (1997-), AMSR-E (2002-),
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report TRMM (1997-), CloudSat, (2006-) MODIS (1999-), and AIRS (2002-) (the last two provide important information on clouds and water vapor). NASA’s upcoming GPM mission is of great relevance to this ECV. International plans for GCOM-W and AMSR F/O (2011) are also of interest. Participants discussed the relevance of the decadal survey’s recommended ACE and PATH missions, which would provide important information on aerosol-cloud interactions and high-temporal-resolution precipitation, respectively. NPOESS CrIS/ATMS measurements will contribute to the precipitation ECV, but questions remain about the still-undefined MIS capability. Some participants expressed concern that a capability for passive microwave precipitation measurements may not emerge in the revised MIS sensor, and they suggested that NPOESS place emphasis on the water cycle (water vapor, liquid water, ice water, and precipitation) when considering MIS requirements, possibly including giant magneto-impedance (GMI) bands. Water Vapor With measurements available through CrIS/ATMS on NPOESS, IASI on MetOp, and ABI on GOES-R, there was little concern expressed about the water vapor ECV. MIS capabilities, still uncertain, should include total column water vapor information. Several participants suggested that the water vapor channel be added back to VIIRS to further strengthen the water vapor ECV, while also benefiting wind and aerosol measurements. Ongoing missions and instruments of relevance include SSM/I (1987-), SSMIS (2003-), (A)ATSR (1991-), AMSR-E (2002-), MERIS (2002-), HIRS (1979-), AIRS/AMSU (2002-), MODIS (1999-), TMI (1997-), and MLS (2004-). International plans include GCOM-W and AMSR F/O (2011). Decadal survey missions of relevance include GPS/RO and PATH. Surface Wind Speed and Direction Measurements of surface wind speed and direction are needed for both climate and operational purposes. For climate, vector winds are required to compute wind stress curl, an essential climate quantity that drives Ekman pumping and suction in the ocean, thereby implying vertical circulations (i.e., upwelling and downwelling). The zonal integral (east to west) of wind stress curl across an ocean basin is proportional to the western boundary current transport (i.e., the transport responsible for the dominant part of the poleward heat flux by the ocean). The climatology of storms (frequency and intensity) depends on vector wind measurement, and measurements are required in all conditions. Several participants noted that the CMIS replacement (MIS) is not expected to meet needs for data on these variables. Several participants also noted that the NPOESS key performance parameter is wind speed only, and so measurement of wind direction is not ensured as trade-offs are explored. Ongoing missions and instruments of relevance to this ECV include QuikSCAT (1999-), ERS (1992-), and WindSat (2003-). The international ASCAT6 measurement and the decadal survey recommendation for XOVWM were also discussed. Participants engaged in a lively debate over the relative merits of passive versus active measurement of surface wind speeds; they also discussed the merits of a future system that would combine the active measurement capabilities of ASCAT with the passive measurements to be provided by MIS. It was the strongly held view of many workshop participants that ASCAT and MIS would be inadequate to meet both operational and climate needs, and that an additional active surface wind speed and wind direction measurement was needed. This ECV was also considered by the oceans breakout group and is further discussed in the summary of its session below. Upper-Air Wind Three-dimensional upper-air wind, temperature, and moisture profiles with high vertical and temporal resolution are key to improved prediction of hurricane track and intensity. The upper-air wind ECV is at moderate risk due to its partial reliance upon both NPOESS/VIIRS (which lacks the water vapor band needed to continue 6 The ASCAT scatterometer is an active instrument; however, it does not provide the wide swath coverage or resolution afforded by QuikSCAT.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report MODIS measurements of polar winds) and GOES-R/HES (for continuous full-disk four-dimensional wind vertical profiling, including diurnal coverage). GOES-R/ABI will provide cloud wind tracking and measurements of clear-sky water vapor layer-integrated winds, including diurnal coverage. Ongoing missions and instruments of relevance to the upper-air wind ECV include AVHRR (1979-), MODIS (1999-), (A)ATSR (1991-), GOES (1975-), Meteosat (1978-), GMS (1980s-), Feng Yun (2000s-), and INSAT (2000s-). The international ADM/Aeolus mission is relevant to this ECV, as is the 3D-Winds mission recommended by the Earth science decadal survey. Upper-Air Temperature The upper-air temperature ECV appears to be in good health with the planned flight of CrIS/ATMS on NPOESS and IASI on MetOp, although several participants noted that the inadequate diurnal coverage could be improved by addition of CrIS to the early AM (0530, descending) NPOESS spacecraft. Ongoing missions and instruments of relevance to the upper-air temperature ECV include MSU (1979-), AMSU (1999-), CHAMP (2001-), COSMIC (2006-), GRAS (2006-), HIRS (1979-), and AIRS (2002-). The decadal survey recommendations for GPS/RO, CLARREO, and PATH are also considered relevant to this ECV. Some participants noted that a geosynchronous Earth orbit (GEO) flight of opportunity to fly GIFTS or another Pathfinder could further recover ability to observe and integrate upper-air temperature across the diurnal cycle. The breakout group also discussed air quality observation needs, though noted that air quality is not currently a GCOS ECV. Climate Data Records Related to Observations of the Oceans The oceans ECV breakout group was tasked to consider six ECVs related to ocean observations: sea level, SST, ocean color, salinity, sea state, and sea ice. Some participants also noted the need for ocean measurement input to several atmospheric ECVs (surface wind speed and direction, precipitation, surface radiation, surface air temperature, and water vapor). A summary of the discussions is provided below, organized according to ECV. Sea Level The 15-year record of sea surface height has provided a record of global sea level rise, built on TOPEX and Jason-1 data records. Discussions at the breakout focused on measures to ensure the continuity of this record, a strong desire among most participants. Ongoing missions and instruments of relevance include Jason-1, ENVISAT, and GFO. NASA plans include a Jason follow-on, the Ocean Surface Topography Mission (OSTM)/Jason-2. There are international plans for an accurate altimeter aboard the European Sentinel-3,7 although it will suffer from tidal aliasing due to a Sun-synchronous orbit. The decadal survey recommendation for a NASA advanced altimetry mission called SWOT is also of key interest. Altimeters on NPOESS could help to provide global coverage and measure ocean heat content. However, the removal of the altimeter from NPOESS is not considered a critical issue for climate, as ALT would not have provided a climate-quality sea surface height record due to the NPOESS Sun-synchronous orbit, nor would it have provided information about inland waters and near-coastal areas. For measurements related to the needs of climate researchers, most breakout participants expressed a preference for free-flyer missions that achieve the same quality as Jason, either as a series of Jason follow-on missions such as Jason-3 followed by SWOT, or as a series of SWOT missions, started by advancing the timeline for the first SWOT mission. Sea Surface Temperature Remote sensing of sea surface temperature (SST) has a long heritage, dating back to 1980. Climate studies require all-weather SST coverage, involving complementary infrared (IR) and microwave observations. IR obser- 7 For information on the European Space Agency’s planned Sentinel series, see http://www.esa.int/esaLP/SEMZHM0DU8E_LPgmes_0.html.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report vations provide high spatial resolution and radiometric fidelity in clear skies, and microwave observations provide SST measurements in the presence of clouds and aerosols. Ongoing missions and instruments of relevance include AVHRR (1979-), (A)ATSR (1991-), Aqua/AMSR-E (2002-), MSG/SEVIRI, GOES imagers, TRMM/TMI, TRMM/VIRI, and Aqua/Terra MODIS (1999-). International plans include OceanSat-1 and -2, Sentinel-3 series (2013-2020), MetOp (B, C, D), GCOM-C, and GCOM-W/AMSR-2. The decadal survey PATH mission is also of interest. On NPOESS, MIS will replace the canceled CMIS (but currently is not slated for inclusion until the second NPOESS spacecraft launches in 2016). Of particular concern to many workshop participants was the expectation that the certified NPOESS MIS configuration will lack the desired band for passive microwave SST (6.9 GHz), which would create a gap in the SST record. Many participants also suggested the need for sustained daily global coverage of the IR observations. Continuity of both IR and passive microwave SST observations on polar and geostationary platforms was considered by many participants to be essential for an accurate and robust SST CDR, as also noted by the International GHRSST-PP science team.8 Continuity by CMIS/MIS with current AMSR-E observations remains a major concern. Ocean Color Tracking of trends in ocean productivity via remote sensing of ocean color is an important aspect of ocean climate study. Measurements of water-leaving radiances are needed, and some participants expressed a desire for a more comprehensive approach than observation and monitoring of chlorophyll. Ongoing missions and instruments of relevance include SeaWiFS (1997-), MERIS (2002-), and Aqua/MODIS (2002-). International plans for OceanSat-2, Sentinel-3, and GCOM-C/SGLI are also of interest, as is the ACE mission recommended by the decadal survey. Ocean color measurements were to be provided by NPOESS/VIIRS and GOES-R/HES. The ocean color ECV is considered at risk due to removal of HES from GOES-R. Ocean color scientists noted that the NPOESS platform and its VIIRS sensor will not be satisfactory for ocean color science, in part because NPOESS does not provide for lunar calibration of VIIRS and in part because of VIIRS hardware issues involving increased optical cross-talk.9 Ocean color researchers at the workshop asserted that observations should have band coverage ranging from UV to shortwave, and they suggested modifying the GCOS ECV to include ocean color records beyond chlorophyll. The ocean biology scientists who were present suggested development of a dedicated ocean biology sensor and mission to accommodate the need for lunar calibration, building on the approach taken by the SeaWiFS instrument. In situ calibration with ocean buoys is also an important consideration. Salinity Measurement of sea surface salinity is a new capability. The European Soil Moisture and Ocean Salinity (SMOS) mission and the NASA Aquarius mission will provide the first satellite sensing of sea surface salinity (which will require measurements of surface wind speed and SST as part of the retrieval process). There is as yet. no satellite climate record to evaluate the results of these missions. Sea State As winds over the ocean change in response to climate variability and climate change, there will be changes in sea state. The sea state is important for marine weather and for the safety of life at sea, forecasts and warnings. 8 For information on the Global High-Resolution Sea Surface Temperature Pilot Project, see http://ghrsst-pp.org. 9 In remote sensing, optical cross-talk is an important error source that results when a detector responds to impinging light from out-of-channel wavelengths (e.g., due to scattering, internal reflections, or other optical leaks). This out-of-channel component of the detector signal can be difficult or impossible to de-convolve with the in-channel (desired) signal. At the time of the workshop, VIIRS was at risk of not meeting the instrument requirement that limits the level of acceptable optical cross-talk. The optical filter assembly in VIIRS, which separates incoming signal into a number of smaller wavelength channels, is known to be the source of the optical cross-talk problem. Efforts are underway to seal light leaks and reduce scattered light. If the VIIRS optical cross-talk issue is not resolved, ocean color and aerosol products will be adversely affected.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Some participants questioned whether the sea state ECV represented a fundamental measurement. From a climate perspective, the roughness of the sea surface plays a role in air-sea exchanges. It would be ideal to have full wave directional spectral capability, spanning surface gravity wave and surface swell periods. This is not at present a satellite capability. Sea Ice With MIS delayed until NPOESS C2, there is a need to continue the long (28-year) climate data record of sea ice extent and concentration collected by passive microwave radiometers; continued scatterometer and altimeter measurements are also required. Changes in sea ice and ice coverage are a critical indicator of climate change. Ongoing missions and instruments of interest include SMMR, SSM/I (DMSP), SSMIS, AMSR-E, QuikSCAT, MODIS, and ASCAT. Planned missions include the DMSP missions, F19 and F20, carrying SSMIS; GCOM-W/AMSR-2; GCOM-C/SGLI; RADARSAT-2; and CryoSat-2. The decadal survey recommendations for SCLP, ICESat-II, XOVWM, and DESDynI are also of interest. With MIS delayed, a passive microwave data gap is anticipated. A synthetic aperture radar or equivalent capability is also needed in the production of the sea-ice climate data record for validation of sea ice concentration and edge. This could be provided by the XOVWM scatterometer. To fill the gap, a free-flyer QuikSCAT replacement combined with an AMSR-type instrument would be a backup against DMSP failures. Surface Wind Speed and Direction From an oceanographic perspective, there is a need for vector wind measurements, and many participants noted that surface vector winds from passive microwave did not fulfill the need for climate-quality surface vector winds and for observation of extreme weather events. Thus, to these participants, the removal of CMIS from NPOESS was not a major issue. Many of the breakout group’s participants indicated the real need to enhance climate measurement capabilities beyond the QuikSCAT standard in a follow-on, active radar surface vector wind mission. The QuikSCAT mission has provided an 8-year record to date and has exceeded its design lifetime. Follow-on options discussed included relying on ASCAT on MetOp, duplicating QuikSCAT, and flying XOVWM (as recommended by the Earth science decadal survey). The XOVWM option has the advantages that that sensor can measure higher wind speeds than can QuikSCAT, can provide improved vector wind retrievals in rain, and can detect surface rain rate. Higher spatial resolution (~1 km) is also desired. It was also noted that the incremental cost of XOVWM versus a QuikSCAT duplicate would be small, in part because QuikSCAT was designed and developed more than a decade ago. Precipitation, Surface Radiation, Surface Air Temperature, and Water Vapor Simultaneous knowledge of the surface forcing of the ocean (heat, water, momentum fluxes from the atmosphere) and ocean-atmosphere exchange is important to monitoring and understanding the ocean’s role in climate. Global ocean remote sensing coverage of rainfall, surface incoming and net shortwave and longwave radiation, and latent and sensible heat fluxes is needed. Latent and sensible heat flux can be parameterized given surface wind, SST, and surface air temperature and humidity. The oceanographic community supports collection of climate-quality surface radiation and rainfall fields. It remains a significant challenge to retrieve surface air temperature and surface humidity from space, and existing data are not considered to be of the quality needed to generate CDRs. Other Discussion Some participants felt that the requirements to instrument selection process did not sufficiently engage the ocean climate user community, and they expressed a continuing need for this engagement to ensure that the missions flown support collection of climate-quality data records. NASA science teams are one model to ensure such engagement. The science team approach has worked particularly well in terms of federating international activities
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report for several CDRs, including SST (the GHRSST-PP), ocean color (International Ocean Colour Coordination Group (IOCCG)), and altimetry (Ocean Surface Topography Science Team (OSTST)). Further, some participants noted that for SST, sea ice, and ocean surface vector winds there is possible synergy and an optimum combination for accuracy, data gap limitation, spatial and temporal resolution, and CDR continuity that should be considered. All three of these CDRs would benefit from sensor collocation. A solution would be to pursue XOVWM and AMSR-type sensors on the same satellite or in formation, and in polar orbit. This approach would entail acceleration of the XOVWM schedule. Another approach would be to modify XOVWM to accommodate passive microwave (6.9 GHz) SST with surface wind speed (required for accurate SST retrievals at 6.9 GHz) together with sea ice monitoring. An XOVWM+SST system in low-inclination orbit would enhance studies of tropical weather and climate. Climate Data Records Related to Observations of the Land The land ECV breakout group was asked to consider 10 ECVs related to surface observations: glaciers and ice caps/sheets, snow cover, soil moisture, fire disturbance, lakes, biomass, land cover, surface albedo, fraction of absorbed photosynthetically active radiation (FPAR), and leaf area index (LAI). The primary NPOESS instrument for land surface climate variables is VIIRS, following the heritage of AVHRR and MODIS sensors. Likewise, for GOES the primary land climate instrument will be the imager (ABI on GOES-R). The first hour or so of the breakout addressed the VIIRS and its known problems, primarily concerning optical cross-talk. The cross-talk as it stands now will affect the aerosol EDRs and the land EDRs, the latter primarily through poor aerosol correction. It is not clear that the cross-talk issue for VIIRS will be fixed in time for its first flight on NPP. Although an improved filter is being constructed and is planned for installation, participants were informed that there remains at least a 30 percent chance that the fixes will not work and that the land EDRs will be out of specification. Participants considered the importance of land ECVs in terms of scientific impact and the availability of longer-term data sets for comparison and study. The land ECVs were then each evaluated in terms of risk. All risk evaluations in this summary assume that the cross-talk issue for VIIRS will be successfully alleviated. Glaciers and Ice Caps/Sheets The glaciers and ice caps/sheets ECV is of importance to climate models and albedo, water balance, sea level, and radiation budget climate studies. Ongoing missions/instruments of relevance include Landsat (1984-), SPOT, ASTER (2000-), GRACE (2002-), ICESat, MODIS (1999-), and MISR (2000-). The international Cryosat-2 mission, currently in its implementation phase, and the ICESat-II, GRACE-II, DESDynI, and SCLP missions recommended by the Earth science decadal survey are also relevant. NPOESS’ VIIRS is expected to contribute to this ECV; however, there is some risk to the ECV associated with the lack of ALT data required to estimate mass balance, although other altimeter measurements (if secured) can meet the need. Snow Cover Measurement of snow cover is a high priority because of snow cover’s role in radiation budget and water cycle studies. Ongoing missions and instruments of relevance include AVHRR (originally VHRR; 1972-), MODIS (1999-), (A)ATSR (1991-), Landsat, SPOT, and SSM/I. NPOESS will contribute via VIIRS and ATMS; however, planned contributions by the CMIS replacement, MIS, are now uncertain. The snow cover ECV is also affected because VIIRS data can be used to map areal extent through time but a height/depth-related measure, which is required to make key calculations of mass, is missing. The decadal survey SCLP mission is relevant to this ECV, as it would provide passive and active microwave measurements of snow water equivalent. GOES-R ABI measurements are also of relevance, as are international plans for Sentinel-3.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Soil Moisture The soil moisture ECV is important to climate science due to its impact on biogeochemical cycling, mesoscale climate models, vegetation dynamics, albedo, and surface roughness. Ongoing missions and instruments of relevance include AMSR-E (2002-), ALOS (2006-), Landsat, MODIS (1999-), and ASCAT (2006-). The planned NASA LDCM mission and international SMOS missions are also of interest. The NPOESS VIIRS and CMIS instruments are relevant to soil moisture; however, the soil moisture ECV is considered at high risk due to the CMIS descope, which effectively eliminates any possibility of retrieving this measurement. Even with CMIS, soil moisture measurements would have been limited to bare or very sparsely vegetated soils. Recommended by the Earth science decadal survey, SMAP, an active and passive L-band mission to directly measure soil moisture, would provide direct global soil moisture measurements with greater penetration depth. Fire Disturbance The fire disturbance record has climate science implications in terms of understanding biogeochemical cycling, disturbance, and disasters. Ongoing missions and instruments of relevance include AVHRR (1982-), (A)ATSR (1991-), SPOT (1998-), Landsat, ASTER, MODIS (1999-), and MERIS (2002-). International plans for GCOM-C/SGLI (2012-2025) and Sentinel-2 are also of interest. VIIRS on NPOESS and ABI on GOES-R are expected to contribute to this ECV; however, there is a moderate risk to the ECV due to the low saturation level of the VIIRS instrument and the lack of VIIRS in a midmorning orbit. The saturation issue prevents the retrieval of fire radiative power,10 which is an important component of this ECV, and the loss of the midmorning orbit reduces the measurement of fire diurnal cycles. Lakes The lakes ECV is of relevance to biogeochemical cycling, eutrophication, mesoscale climate models, human impact, vegetation dynamics, water cycle, and radiation budget climate studies. Ongoing missions and instruments of relevance include ERS-2/AATSR (1995-), MERIS (2002-), SeaWiFS (1997-), Jason-1 (2001-), Landsat (Landsat-7, 1999-), SPOT (SPOT-5, 2002-), and AVHRR (on NOAA POES). NASA plans for OSTM/Jason-2 and LDCM, international plans for Sentinel-3 and GCOM-C/SGLI, and the decadal survey recommendation for SWOT are also of interest. NPOESS/VIIRS can address the surface area of lakes; however, there remains a lack of three-dimensional measurement capability. Biomass Measurements of biomass are important to studies of biogeochemical cycling, modeling, mesoscale climate models, human impact, vegetation dynamics, and surface roughness. Ongoing missions and instruments of relevance include ALOS/PALSAR (2006-), ENVISAT/ASAR, Landsat, MODIS (1999-), MERIS (2002-), ICESat, and ASTER. NASA plans for LDCM, international plans for Cryosat-2, ALOS, and ESA-BIOMASS, and the decadal survey recommendations for DESDynI and ICESat-II are also of interest. NPOESS/VIIRS is expected to contribute to this ECV; however, there remains a lack of three-dimensional measurement capability (e.g., from lidar or radar). 10 It has been demonstrated in small-scale experimental fires that the amount of radiant heat energy liberated per unit time (the fire radiative power; FRP) is related to the rate at which fuel is being consumed. This is a direct result of the combustion process, whereby carbon-based fuel is oxidized to CO2 with the release of a certain heat yield. Therefore, measuring this FRP and integrating it over the lifetime of the fire provides an estimate of the total fire radiative energy (FRE), which for wildfires should be proportional to the total mass of fuel biomass combusted. See M.J. Wooster, G. Roberts, G.L.W. Perry, and Y.J. Kaufman, “Retrieval of biomass combustion rates and totals from fire radiative power observations: FRP derivation and calibration relationships between biomass consumption and fire radiative energy release,” Journal of Geophysical Research 110:D24311, doi:10.1029/2005JD006318, 2005.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Land Cover, Surface Albedo, Fraction of Absorbed Photosynthetically Active Radiation, and Leaf Area Index The above ECVs are important to climate studies due to their role in biogeochemical cycling, modeling, mesoscale climate models, human impact, vegetation dynamics, albedo, and surface roughness. Ongoing missions and instruments of relevance include AVHRR, MODIS (1999-), (A)ATSR (1991-), Landsat, SPOT, MERIS (2002-), GLI, ASTER, MISR (2000-), GOES, MSG, and POLDER. The NASA-planned LDCM mission, the international plans for Sentinel-3 and GCOM-C/SGLI, and the decadal survey recommendation for HyspIRI are also of interest. These ECVs are considered to be at low risk because they can be adequately addressed by VIIRS (assuming cross-talk is mitigated). If the VIIRS cross-talk issue is not resolved, there will be moderate risk to these ECVs. WORKSHOP SUMMARY—DAY 2 The breakout groups on day 2 focused on the impacts of NPOESS and GOES-R descopes sensor by sensor. Participants were asked to comment on the various mitigation options suggested by NASA and NOAA presenters on day 1 and to suggest other mitigations to recover lost capabilities of importance to the climate community. Where appropriate, participants also considered whether missions in the Earth science decadal survey mission set might enable the recovery of the NPOESS climate measurements.11 As on day 1, templates were filled in during the breakout sessions, and they are available online.12 After the workshop a short background section was added to each breakout session summary to provide context for the discussions. It is important for the reader to recognize that the mitigation options presented below do not include all that might be considered and that both the options and the analysis are necessarily the subjective and not always disinterested views of presenters and participants. Breakout Sessions Radiation Sensor Measurements Background TSIS, ERBS, and OMPS-Limb measure, respectively, the incoming solar energy, the energy reflected and emitted by Earth, and the height-dependent concentration of atmospheric ozone that modulates these energy fluxes. Since the balance of incoming and outgoing radiation (Figure 2.1) determines Earth’s global temperature, these quantities are critical physical components of climate variability and change. The 28-year-plus time series of total solar irradiance, total ozone, and outgoing longwave radiation allows researchers to address unique aspects of climate change, climate sensitivity, and cloud feedbacks; however, questions remain. Termination of the solar irradiance, energy budget, and ozone profile time series will leave unanswered crucial questions concerning the Sun’s impact on climate, both from direct surface heating and indirectly through its modulation of ozone and the stratosphere; the recovery (or not) of the ozone layer from chlorofluorocarbon reductions; the climatic impacts of a changing stratosphere; and the high-precision monitoring of clouds, aerosols, and ocean heat storage over the globe. Total and Spectral Solar Irradiance The TSIS instrument that would have flown on NPOESS comprises the Total Irradiance Monitor (TIM) and Spectral Irradiance Monitor (SIM) components, copies of which are currently operating successfully on the NASA SORCE (Solar Radiation and Climate Experiment) free-flying spacecraft (launched in 2003). 11 The decadal survey missions represent a set of community consensus priorities spanning Earth science including, but not limited to, climate science. Participants were asked to consider whether missions in the decadal survey mission set might enable recovery of NPOESS climate measurements to determine whether there are opportunities for synergism between NPOESS climate measurement recovery strategies and implementation of the community consensus decadal survey plan. Mitigation strategies were considered entirely within the context of climate measurement recovery and are not to be construed as a review of decadal survey mission priorities. The notion of synergy versus competition with the decadal survey is further discussed in Chapter 3, “Cross-Cutting Issues.” 12 See http://www7.nationalacademies.org/ssb/SSB_NPOESS2007_Presentations.html.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report FIGURE 2.1 Diagram of Earth’s radiation budget identifying the components that the three demanifested NPOESS sensors were to measure. SOURCE: After NASA Langley Research Center, “The Earth’s Energy Budget,” CERES S’COOL Project: Clouds and the Earth’s Radiant Energy System Students’ Cloud Observations On-Line. Available at http://asd-www.larc.nasa.gov/SCOOL/budget.jpg. The SORCE TIM sensor provides improved absolute accuracy and long-term stability relative to the radiometers flown on the Nimbus-7, Solar Maximum Mission, Upper Atmosphere Research Satellite (UARS), ACRIMSAT, and SOHO spacecraft. ACRIMSAT (launched in 1999) and SOHO (launched in 1995) are still operating. The SORCE SIM instrument is the first to measure the visible and near-infrared spectral irradiances, and it continues the monitoring of the middle UV spectrum, done earlier by UARS. A TIM instrument is scheduled to fly on the Glory mission (launch in late 2008, 3-year mission design lifetime, 5-year goal), after which there are no current plans to ensure continuation of the 35-year record of total solar irradiance. The end of the SORCE mission in 2011 (assuming a 4-year extension of the core 5-year mission) will terminate a 9-year record of solar visible and infrared spectral irradiance and a 20-year record of solar ultraviolet spectral irradiance. Solar irradiance measurements from 1978 to 2013 will have sampled only three 11-year irradiance cycles, which alone is insufficient time to determine whether long-term irradiance trends occur or to quantify the broad range of irradiance changes possible in activity cycles of varying strength.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report make the AMSR-2 data and the supporting documentation that is required to develop CDRs freely available to the research community. The workshop discussion stressed the need for proper documentation for each satellite data stream to be freely available to the user community as an aid to application of the data within the CDR. In addition, science teams need to be funded to utilize the AMSR-2 data for climate research. However, there were some concerns expressed about relying too much on AMSR-2 because of past problems with platform stability and longevity, and some additional mitigation was thought to be highly desirable. Mitigation Scenario 2. The second mitigation scenario is to add a 6.9 GHz channel to GMI. Currently the lowest channel on GMI is 11 GHz, and it is feasible that a 6.9 GHz channel could share the same feedhorn as the 11 GHz channel. It is also possible that the size of the GMI antenna could be increased. However, the GMI project has already undergone several delays, and it is not clear if these new modifications would be possible considering the current schedule. Another drawback is that SST in polar areas will not be observed by GMI. Mitigation Scenario 3. The third mitigation scenario, most intriguing to many participants, is to enhance the microwave radiometer onboard the planned (but not yet funded) XOVWM, which has a suggested launch date around 2012. The synergy of an active scatterometer and a passive radiometer on the same platform is significant and would improve both the scatterometer vector wind retrievals and the radiometer SST retrievals. As currently planned the XOVWM radiometer has channels at 6.9 and 14 GHz. It also has a very large antenna that will provide higher spatial resolution than would AMSR-E. To obtain accurate SST retrievals, at least one higher-frequency channel would be required and the onboard calibration system would have to be improved. The feasibility of these enhancements needs to be investigated. Mitigation Scenario 4. A final mitigation strategy is a free-flyer radiometer with AMSR-type capabilities. Existing radiometers such as GMI (with a 6.9 GHz channel), JAXA AMSR-2, or WindSat are all possibilities. However, this would be a costly scenario in that it would require an entirely new mission. Other Breakout Group Discussions. In addition to mitigation strategies, a few other matters were discussed, including the idea of reinstating microwave sounding channels on the morning NPOESS platform. For this purpose, ATMS is preferable to sounding channels on MIS. Interest in this approach comes from the need to continue the MSU/AMSU tropospheric and stratospheric temperature CDRs without any spurious discontinuities. These temperature time series have been based on a combination of morning and afternoon orbits for the last 28 years and represent one of the most important CDRs coming from satellite remote sensing. Scatterometry. Breakout group participants discussed the CDR that exists thus far for ocean vector winds, based primarily on 8 years of QuikSCAT measurements. Other platforms’ contributions were discussed, including those of ASCAT and WindSat. These discussions are briefly described here, although the discussion was extensive. Some participants noted that the currently operating ASCAT scatterometer on MetOp will not maintain the CDR established by QuikSCAT, primarily because of sampling inadequacy; the combined coverage of the two parallel measurement swaths of ASCAT is only approximately 55 percent that of QuikSCAT. The 720 km gap between the two ASCAT swaths exacerbates these sampling problems. In addition, the spatial resolution of ASCAT is half that of QuikSCAT, which limits ASCAT’s usefulness in coastal applications to those that are about 50 km or farther from land, and in the resolution of small-scale features in the wind field such as hurricane structure, fronts, and jets. ASCAT also has a different wind directional ambiguity structure that results in larger potential errors in the interpretation of vector wind fields. Further, because of the reduced sensitivity of vertically polarized radar returns to high winds compared with horizontal polarization and the fact that ASCAT is a single-channel vertically polarized radar, the performance of ASCAT in high-wind conditions remains to be demonstrated. Some participants also remarked on the difficulty of assessing the accuracy of WindSat estimates of wind speed and direction due to frequent updates of the wind retrieval algorithms under development by the Navy, although the evolving nature of these algorithms was not considered surprising in view of the newness of the passive microwave
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report technology for measurements of ocean surface vector winds. In presentations to the participants, WindSat wind retrievals (based on 4 years of data) were compared with QuikSCAT observations. Based on analyses of these comparisons, the following observations were made: There is significantly larger wind direction uncertainty in WindSat retrievals at low-to-moderate wind speeds; Depending on the version of the algorithm, WindSat wind retrievals can be biased either high or low in high-wind-speed conditions such as hurricanes and extratropical cyclones; WindSat retrievals of wind vectors are more susceptible to error in cloudy and rainy conditions, which are often associated with extreme weather events; this susceptibility may affect the use of WindSat data in forecast systems and for wind warnings and the development of accurate climatologies of such events; The spatial resolution of WindSat is less than half that of QuikSCAT; The coverage of the WindSat measurement swath is only approximately 55 percent that of QuikSCAT; and Passive measurements are much more subject to contamination by land in the antenna sidelobes; as a result, WindSat’s retrievals are not possible within approximately 75 km of land. While some of these issues are being addressed by ongoing improvements in the WindSat retrieval algorithms, several participants expressed the strongly held view that passive microwave measurements would never be comparable in accuracy, coverage, or resolution to the measurements from a radar scatterometer. Passive microwave measurements would be especially problematic in cloudy and rainy conditions and for measurement of winds near land. In the certified NPOESS program, CMIS has been descoped to MIS, which has not yet been defined in detail. Participants frequently commented that CMIS was adopted with no input from the scientific user community and with limited evidence of the capabilities of passive microwave for estimation of ocean surface vector winds. Regardless of whether MIS includes the polarimetric measurements required to estimate wind direction, it would result in a degradation of the accuracy, coverage, and resolution of ocean vector winds provided by QuikSCAT, especially in rainy conditions. Moreover, MIS would worsen the sampling of the wind field near land compared with QuikSCAT. MIS is therefore not a viable mitigation strategy for maintaining the ocean surface vector winds CDR. India and China plan to launch scatterometers in 2008 and 2010, respectively. The instrument designs for these scatterometers are unknown and data availability remains uncertain for both missions. Neither of these scatterometers can therefore be considered viable mitigation strategies for continuation of the ocean surface vector winds CDR. While QuikSCAT has provided many benefits and has established a baseline CDR for ocean surface vector winds, there are important limitations to the QuikSCAT data. For example, the Ku-band QuikSCAT radar cannot measure extreme winds or winds in heavy rain (although it can measure wind speeds of up to about 90 kt, if those winds occur outside of rain and are not confined to a very small area, both of which are the case in most hurricanes). QuikSCAT measurements are also limited to a spatial resolution of 12.5 km and are not routinely made closer than about 30 km from land.26 Many in the microwave breakout group argued that high priority should be given to a sustained, more capable, next-generation scatterometer program that can meet these requirements while at the same time continuing the ocean surface vector winds CDR established by QuikSCAT. Since QuikSCAT is already 3 years past its designed instrument lifetime, it was a widely held view that continuation of the ocean surface vector wind CDR is in serious jeopardy. None of the currently operating or future planned instruments can continue the ocean surface vector winds CDR. Two mitigation scenarios were discussed. Both consist of a dedicated free-flyer scatterometer mission at the nearest possible opportunity in order to avoid, or at least minimize, a gap in the ocean surface vector winds CDR. This mission is envisioned as the first in a sequence of such missions. 26 See “Oceans Community Letter,” April 6, 2006, available at http://cioss.coas.oregonstate.edu/CIOSS/Documents/Oceans_Community_Letter.pdf.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Mitigation Scenario 1. The first scenario involves a QuikSCAT clone, which is the minimal solution for continuing the accuracy, resolution, and coverage of the 8-year ocean surface vector winds CDR established by QuikSCAT. The advantage is that a QuikSCAT clone is preliminarily estimated by NASA to be approximately 10 percent less expensive and could be readied 6 months sooner than the advanced scatterometer considered in the second scenario. The small percentage cost differential is because QuikSCAT is based on 1980s technology that would have to be updated to currently available electronic components. This updating would lead to a redesign of major instrument subsystems, thereby losing many of the cost advantages of a true “build-to-print” duplication of the QuikSCAT instrument. The disadvantage of a QuikSCAT clone is that some of the most important NOAA operational requirements established at the June 2006 NOAA Operational Ocean Surface Vector Winds Requirements Workshop27 would not be met (e.g., measurements of extreme winds, higher spatial resolution, and reduced contamination from rain and land). Mitigation Scenario 2. The second scenario, preferred by many participants, consists of a next-generation synthetic-aperture-radar-based scatterometer mission referred to in the Earth science decadal survey as XOVWM. XOVWM would include a dual-frequency Ku-band and C-band radar and an X-band radiometer, which would allow measurements in rainy conditions, as well as measurements of the extreme winds in hurricanes and extratropical cyclones. The next-generation system would provide measurements with a resolution of better than 5 km and to within 1-3 km of land. XOVWM would thus satisfy most of the NOAA operational requirements, while at the same time maintaining the ocean surface vector winds CDR established by QuikSCAT and beginning a more accurate record of strong storms at sea, including hurricanes. The relatively minor disadvantages of XOVWM over a QuikSCAT clone are an approximate 10 percent cost increase (based on preliminary NASA estimates) and a 6-month longer delay to launch. The minor cost increase for XOVWM versus a QuikSCAT clone reflects the reality that even an attempt to duplicate the existing QuikSCAT would incur many of the nonrecurring costs of XOVWM, in part because of the long delay since QuikSCAT’s initial development and the obsolescence or unavailability of the hardware components used. XOVWM is a mission recommended in the decadal survey; several workshop participants argued that the proposed schedule for launch of this mission—2013-2016—be accelerated. Finally, while discussing this mitigation scenario, some participants indicated the desirability of an enhanced XOVWM+SST mission, a point that was also made during day 1 discussions. Geostationary Hyperspectral Measurements GOES-R is being developed as NOAA’s next generation of geostationary weather satellites. In late 2006, following large increases in estimates for completion of the program, NOAA canceled plans to incorporate a key instrument on the spacecraft—HES. HES was planned to provide both an advanced sounding capability for measurements of atmospheric temperature and moisture content and an imager for monitoring coastal water quality and assessing coastal hazards. Background on the HES instrument, along with a summary of the breakout participant discussions, is provided below. Background Geostationary sounders provide unique, rapidly updated moisture profile measurements. In 1980, through the Operational Satellite Improvement Program (OSIP), NASA and NOAA partnered to fly a critical demonstration mission—the Visible and Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS). VAS was the first atmospheric temperature and moisture profiler flown in GEO. Subsequent three-axis-stabilized operational GOES-I-class sounders significantly improved upon VAS’s precision and have collected long-term records of atmospheric variables and diurnal cycles over the Western Hemisphere through the present time. These measure- 27 The NOAA Operational Ocean Surface Vector Winds Requirements Workshop, held June 5-7, 2006, at the National Hurricane Center in Miami, Florida, was sponsored by the Office of the Federal Coordinator for Meteorology. The final report of the workshop is available at http://www.ofcm.gov/tcr/reference/Ocean%20Surface%20Vector%20Winds_workshop_report_final.pdf.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report ments will continue through the flight of the GOES-N/O/P series. With the termination of the GOES-R sounder, these long-term records will end. The value of sounding from GEO, however, goes beyond maintenance of a long-term record. The ability to sense water vapor in the atmosphere is crucial for monitoring and predicting hazardous weather conditions. Large variations in atmospheric water vapor occur over fine scales of 10 km in the horizontal and 1 km in the vertical, and over tens of minutes; therefore, high-temporal-resolution monitoring is essential. The current GOES-N-class sounder temperature and moisture profiles provide relatively coarse temporal and spatial coverage, which is informative for indicating the synoptic-scale severe weather threat to areas, but insufficient for “nowcasting” cell development on the mesoscale or adequately resolving boundary-layer structures critical for nowcasts of severe thunderstorms. Summary of Breakout Group Discussion The GOES-R/HES breakout group session focused on mitigation options to restore the high-vertical-resolution temperature and water vapor sounding products and associated derived products planned for the HES payload on the GOES-R series. The breakout group did not address the coastal water imager because the ocean color community was not sufficiently represented. As noted above, the reader is advised that the options presented do not include all that might be considered, and that both the options and the analysis are necessarily the subjective and not always disinterested views of presenters and participants. The breakout group heard a presentation regarding the importance that high-temporal-resolution hyperspectral observations of key atmospheric state variables and their trends have for climate data records. Such measurements are not easily made except from a geostationary orbit. The role of geostationary hyperspectral measurements in characterizing diurnal variations, identifying the sources, sinks, and transport of pollutants and greenhouse gases, and a potential key role in sensor intercalibration,28 were also discussed. The case was then presented for advanced geostationary sounding capabilities as a contribution to GEOSS societal benefit areas, atmospheric ECVs, Numerical Weather Prediction capabilities improved by four-dimensional data assimilation, nowcasting capability, and sensor intercalibration.29 The value of nonclimate applications of such measurements was emphasized. A presenter then reviewed the NESDIS Office of Systems Development Analysis of Alternatives (AoA) study,30 which considered a broad array of advanced geosynchronous sounder alternatives and trade-offs. The AoA study’s conclusions were discussed, particularly the need for an advanced sounder and space-based technology demonstration as early as feasible. It was suggested that previous ground system cost estimates were driven up by the inclusion of the coastal waters imager and that a recent proposal by NESDIS/STAR,31 considering only the advanced sounder in a demonstration mode, reduced the cost estimates significantly from the original estimates. In addition, the presenter noted the similarities between the AoA and Earth science decadal survey recommendations, which endorse the need for (at reasonable cost and risk) an operational advanced imaging sounder for GOES and an early demonstration. GIFTS was then introduced as a potentially viable option to get a demonstration instrument into GEO as early as possible. The presenter suggested that if launch services could be identified, such a mission could be done for approximately $150 million. This proposed track would not interfere with the GOES-R schedule but would retain the timing necessary to influence the design of the operational version for GOES-T. Concurrently, the presenter argued, reduced-capability advanced sounders should be developed for the GOES series. 28 For example, geostationary hyperspectral sounders are identified as a key component of a Global Space-Based Inter-calibration (GSICS) system. See http://www.star.nesdis.noaa.gov/smcd/spb/calibration/icvs/GSICS/index.html. 29 P. Ardanuy, B. Bergen, A. Huang, G. Kratz, J. Puschell, C. Schueler, and J. Walker, “Simultaneous Overpass Off Nadir (SOON): A method for unified calibration/validation across IEOS and GEOSS system of systems,” in Atmospheric and Environmental Remote Sensing Data Processing and Utilization II: Perspective on Calibration/Validation Initiatives and Strategies (A.H.L. Huang and H.J. Bloom, eds.), Proceedings of SPIE, Volume 6301, 2006. 30 NESDIS and OSD, Analysis of Alternatives, 2007. Participants in the AoA study included NOAA/NESDIS offices, university/cooperative institutes, contractors, DOD, and NASA. 31 NESDIS/STAR (Center for Satellite Applications and Research) is the new name for the former Office of Research and Applications.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Some attendees at the breakout group argued forcefully that an advanced sounder with HES-like capabilities would revolutionize short-term prediction, most notably of severe weather. Some workshop participants also referenced a NOAA/NESDIS-commissioned analysis of the potential economic benefits of the GOES-R ABI and HES instruments,32 which supported the economic justification for a HES-like capability. Advocates for including HES-like capabilities on GOES-R, which in this self-selected breakout group seemed to be most of the attendees, were very displeased by the indication during a plenary presentation by a NOAA official that an advanced hyperspectral sounder was “off the table” for GOES-R/S, and would most likely be next considered as a demonstration instrument on GOES-T. Some participants suggested that NASA and NOAA partner to achieve earlier GEO hyperspectral sounder capability, taking advantage of the inherent strengths of both agencies (and reinvigorating the OSIP). Mitigation Scenario 1. Scenario 1 involves use of simulated sounder products taking advantage of only ABI observations. Many participants considered this option to be generally undesirable, as ABI lacks spectral, and therefore vertical, resolution and would be unable to provide the many products expected from HES. Mitigation Scenario 2. Scenario 2 involves adding CrIS/ATMS back to the early morning (05:30) NPOESS orbit platforms. This remanifesting would add a useful additional pair of diurnal observations that would provide hyperspectral information. It would not, however, approach the temporal refresh available from geostationary orbit. Mitigation Scenario 3. Participants suggested a scenario involving an opportunity for an early demonstration of GEO hyperspectral capabilities by launching GIFTS on a near-term flight of opportunity (i.e., free flyer or international partnership) to advance user readiness and allow algorithm development. It was noted that savings in nonrecurring engineering would be lost with this approach, as the demonstration unit (i.e., GIFTS) would not be the same as subsequent units, requiring subsequent demonstrations. Flight of an engineering model (rather than GIFTS) as a demonstration was seen as a way to save on nonrecurring engineering costs. However, there were differences of opinion among the group on the question of whether it would be less expensive or more desirable to launch GIFTS, build a different early demonstration model, or build the first flight model of the desired sounder. Mitigation Scenario 4. Another potential approach to retaining (and advancing) the sounder capabilities on GOES was presented by a representative of ITT Space Systems who argued that the ITT “ABX” sounder is a simpler approach that could bridge the gap between the GOES-N legacy sounder and a full hyperspectral sounder on GOES-T. For GOES-R, the ABX would involve 18 sounding channels by reducing the ABI scan rate to improve the signal-to-noise ratio. This could “evolve” into a full hyperspectral capability by GOES-T using the preplanned product improvement (P3I) track. This option would allow retention and enhancement of existing capabilities, provision of GIFTS-like bands, and the potential for extensive reuse for subsequent flights. The perceived negative aspect of this solution is that a full hyperspectral demonstration may be delayed until GOES-T. Other proposed GOES-R series sounder options and paths have been considered by industry; given the competitive nature of such options, however, the representatives at the workshop indicated that they were not at liberty to share the specifics. Other Discussions. It was stated that much of the cost of HES was attributable to the ground system requirements of NPOESS, which are driven by latency requirements. However, according to participants at the breakout session, latency is not a large concern of the hyperspectral community. Thus, most participants also argued that the cost savings that could result from a relaxation of the latency requirement should be pursued. Indeed, the demonstration mode referred to by presenters largely implies relaxation of latency as a cost-savings strategy. Due to session time limitations, the HES breakout group was not able to consider the merit of a HES Observing System Simulation Experiment (OSSE).33 However, an expert on OSSEs provided a background handout for the group 32 Centrec Consulting Group, LLC, An Investigation of the Economic and Social Value of Selected NOAA Data and Products for Geostationary Operational Environmental Satellites (GOES). GOES-R Sounder and Imager Cost/Benefit Analysis, NOAA/NESDIS, 2007. The economic analysis suggested that the inclusion of hyperspectral sounding capability in addition to ABI would nearly double the socioeconomic benefit of GOES-R from $2.4 billion to $4.3 billion. 33 For details on OSSEs, see http://www.emc.ncep.noaa.gov/research/osse/.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report and suggested to the chair of the session that a mesoscale OSSE for the HES instrument could be extremely valuable if done correctly. However, it would require considerable development and a great deal of caution for the conclusions of such a study to be deemed credible. Such a mesoscale OSSE has, to the workshop participants’ knowledge, never been done. Additional comments on the OSSE topic by European experts during the international videoconference session on day 3 suggested that the HES OSSE would be very difficult and likely not possible in a timely manner. WORKSHOP SUMMARY—DAY 3 Plenary Session on International Considerations On Thursday morning, the workshop held a joint international session, through videoconference, with participants at the World Meteorological Organization (WMO) “Workshop on the Re-design and Optimization of the Space-based Global Observing System” that was underway in Geneva, Switzerland. WMO workshop participants included high-level representatives of operational and research and development space agencies, the Committee on Earth Observations Satellites (CEOS), Global Climate Observing System (GCOS), the WMO Space Programme, the WMO Open Programme Area Group/Integrated Observing System (OPAG/IOS), and the Expert Team on Evolution of the Global Observing System (ET-EGOS). That workshop is expected to result in recommendations for both weather and climate monitoring from space being forwarded to the appropriate levels of WMO, the Coordination Group for Meteorological Satellites (CGMS), and CEOS. Anthony Hollingsworth (European Centre for Medium-Range Weather Forecasting; ECMWF) also participated in the videoconference from Reading, England. WMO coordinates efforts for meeting the needs for climate information, such as for climate monitoring, climate-data management, climate-change detection, seasonal-to-interannual climate predictions, and assessments of the impacts of climate change. In the view of WMO representatives, measurements of the climate system should be considered as an operational requirement, and climate monitoring and climate measurements should be given equally high priority within the Global Observing System (GOS). In the WMO Rolling Review of Requirements process, climate requirements are represented by the GCOS Implementation Plan. The WMO presentation noted that taken as a whole, there has not been a concerted strategy for sustained climate observations from space. Instead, the climate community has relied on suboptimal sensors to create a climate record, resulting in significant challenges in terms of handling bias differences, orbit drift, data gaps, and spectral differences between follow-on instruments when reprocessing multiple-satellite data—often at considerable cost. The CEOS presentation provided valuable insight into how various thematic issues could be addressed on a global basis utilizing the CEOS constellation concept, which considers virtual constellations of research and operational satellites to meet observational needs. Study teams have been established and international cooperation among space agencies has been stimulated to explore four representative Constellation prototypes, including atmospheric composition, global precipitation, land surface imaging, and ocean surface topography. It was noted by several speakers that the impact of NPOESS descoping was immediately significant in terms of GOS/GCOS planning and the quality of the CDRs for several variables. The Global Monitoring for Environmental Security (GMES) and climate modeling presentation addressed key uncertainties identified by the IPCC Fourth Assessment report,34 global satellite provisions for atmospheric composition in the 2003-2019 time frame, European launch plans for 2007-2015, the GMES Sentinel program, and progress on the Global and regional Earth-system (Atmosphere) Monitoring using satellite and in situ data (GEMS) atmosphere project at ECMWF. The need for hyperspectral observations from geostationary satellites was also addressed, including a discussion of their potential role in calibration of the space-based observing system (within those spectral ranges); monitoring of the diurnal cycle; and provision of spectrally resolved radiances (hyperspectral visible/near-IR and IR) as a climate reference. Barbara Ryan, U.S. Geological Survey, reminded the teams that CEOS was strongly promoting an integrated observing system that included in situ data for ongoing verification and validation of satellite observations. In 34 Intergovernmental Panel on Climate Change, Climate Change 2007, IPCC Fourth Assessment Report, Cambridge University Press, Cambridge, U.K., 2008, available at http://www.ipcc.ch/ipccreports/assessments-reports.htm.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report situ data are essential and complementary to the space segment data streams, enabling long-term monitoring of satellite data quality and as an independent component of the long-term climate record. A number of other important considerations were brought forth during the videoconference. The importance of sustaining climate-quality climate data from space was addressed, along with the need to keep valuable space assets in operation after they have passed their design lifetime (e.g., Terra, Aqua, and Aura, which provide data for a variety of applications). There was recognition of the importance of determining how to preserve the heritage of past and current instruments with the natural evolution to advanced future instruments for extending climate records. It was further recognized that with limited financial and human resources, a response to GCOS requirements can be achieved only through enhanced international cooperation. Such cooperation should involve global planning with international contributions, in such a way that implementation problems encountered by an individual agency do not dramatically affect the global system. It was recognized that a number of missions planned in Europe will be of great value for climate analysis and that there is an acute need for better international collaboration and awareness spanning the full spectrum of activities from high-level data access agreements to pragmatic documentation exchange. Concerning the NPOESS configuration, many participants supported: Remanifesting hyperspectral IR and microwave sounders in the early morning orbit—both for operational purposes and for reanalysis and climate-related activity. Maintaining continuity of microwave SST measurements at 6.9 GHz (AMSR-E type). With the loss of CMIS on C1 and increasing concern regarding the health of the AMSR-E on-board Aqua (indications of a failing antenna bearing), there is a significant risk of a microwave SST data gap prior to the launch of the Japanese GCOM mission; this could be addressed by the future MIS. Maintaining a high-precision Jason-type altimeter in non-Sun-synchronous orbit (to mitigate the impact of tidal aliasing on sea level measurements) complemented by at least two other altimeter missions (Sentinel-3 will be one) in a Sun-synchronous orbit. This was stated as an urgent need by many participants. Flying a CERES-class instrument for continuity of Earth radiation budget measurements. Accelerating development of an active vector wind mission to replace QuikSCAT. Finally, during the closing plenary session, there was discussion again of the requirements for constructing, managing, and maintaining CDRs. As in previous sessions, participants discussed the intellectual and resource challenges in developing CDRs, which require attention and adequate budgets in the space segment, ground segment, and CDR production units themselves. It was noted that at present, the last is often limited in resources so that problems with satellite data are only discovered following dedicated ad hoc CDR processing projects. Some participants stated that considerable cost benefits would almost certainly be realized if CDR processing could be sustained in an operational near-real-time-style environment. A general theme of the videoconference echoed the need for organizations to work together with synergies among international satellite programs and the importance of multilateral agreements in addressing climate monitoring. In the future, it is through effective international cooperation and global partnerships that useful climate monitoring from space will be realized. A frequently expressed sentiment was that the joint Geneva-Washington session was extremely important in terms of bringing the international satellite climate community together and that such communication should be encouraged through future meetings. Breakout Sessions The breakout groups on day 3 were loosely organized to enable participants to offer comments. Two panels were given specific topics, namely, to assess the NASA-NOAA suggested mitigation options and to further explore the intricacies of CDR development. These two breakout sessions are summarized here. A third breakout session allowed participants to comment on any topic within the scope of the workshop, and key points have been integrated into this report where relevant (many are covered in Chapter 3) and will be considered further during a follow-on study.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Panel to Assess NASA-NOAA Mitigation Options The breakout panel reviewed a summary (see Appendix C) of the draft NASA-NOAA white paper titled “Mitigation Approaches to Address Impacts of NPOESS Nunn-McCurdy Certification on Joint NASA-NOAA Goals.”35 The Office of Science and Technology Policy (OSTP) had asked NOAA and NASA to provide this analysis of possible options for mitigation of the climate research impacts of the NPOESS Nunn-McCurdy certification through 2026, along with an assessment of the potential costs of these options, with the primary goal of ensuring the continuity of long-term climate records. The primary goal of the NASA-NOAA white paper was to identify means for ensuring the continuity of long-term climate records. NASA noted that the white paper was based on a single sentence from the June 5, 2006, Nunn-McCurdy Acquisition Decision Memorandum: “[The restructured program] does not include funding for the following sensors: APS, TSIS, OMPS-Limb, ERBS, ALT, SuS, and the full SESS; however, the program will plan and fund for integration of these sensors onto the satellite buses, if the sensors are provided from outside the program.”36 The options presented in the draft white paper represent a departure from the traditional NPOESS/EOS/MetOp big-platform approach. They are a combination of NPOESS operational flights, accommodations of opportunity, and “climate free flyers.” These focused missions would be dedicated to a limited number of specialized sensors; simpler instruments could have dedicated functions (e.g., to separate reflective from emissive bands). The apparent intent is to use a constellation approach to obtain as many complementary measurements as possible through formation flight. The panel was encouraged by the imagination shown by the NASA-NOAA team and was extremely supportive of their ideas for implementation flexibility—specifically including flights on diverse platforms, including formation flight with NPOESS. However, the white paper options focused on only five instruments: TSIS, ERBS/CERES, ALT, OMPS, and APS. NASA noted that the white paper does not consider mitigation options for VIIRS, CrIS/ATMS, CMIS/MIS, and SESS. Some workshop participants commented that the lack of attention to the other instruments should not be construed as a de facto lower prioritization of their suitability as options for mitigation of lost capabilities. NASA and NOAA will expand the white paper options to consider the other sensors that will fly, revising the white paper based on comments from this workshop. They plan to deliver a revised draft to OSTP by late summer. Panel on Issues Related to CDR Development Underemphasized during certain sessions of the workshop, but recognized as fundamental for ensuring the climate record from space, is the technical issue of generating the needed CDRs from the operational EDRs. Crucial issues include the accommodation of ancillary observations critical for CDRs but absent from the current and planned satellite systems, and the ability to adequately develop and maintain CDRs. The breakout session considered requirements for CDRs (particularly in contrast to EDR retrievals) and the adequacy of current (post-Nunn-McCurdy) plans for prelaunch instrument calibration and characterization; on-orbit calibration and validation; measurement overlap and replenishment requirements; and data storage, archiving, distribution, reprocessing, analysis, and interpretation concerns. Presenters and many participants at the breakout session echoed a concern that the fundamental definitions of EDRs and CDRs and the requirements for CDR generation and maintenance are not adequately understood by the operational and research community. Proper communication of requirements for CDRs requires that these distinctions be clearly understood. According to presenters from the NOAA National Climatic Data Center, even though the sensor signals used to generate EDRs are also used for CDRs, the EDRs themselves are frequently of little use for climate research. EDRs are (in general) poorly calibrated, quick-turnaround products that lack long-term repeatability, whereas CDRs are fully calibrated time series having high precision (repeatability) and accuracy, often requiring reprocessing of entire data sets as algorithms are improved (Box 2.1). 35 Joint NASA-NOAA Study for OSTP (Phase II), June 19, 2007. The report does not consider GOES-R. 36 Under Secretary of Defense for Acquisition, Technology and Logistics, Acquisition Decision Memorandum, dated June 5, 2006, Office of the Secretary of Defense, Washington, D.C.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report BOX 2.1 Generation of Climate Data Records The instruments and data system for NPOESS are designed to produce a number of operational geophysical products, which are called environmental data records (EDRs). EDRs are generally produced by applying an appropriate set of algorithms to raw data records. Although NPP- and NPOESS-derived EDRs may have considerable scientific value, climate data records (CDRs)a are far more than a time series of EDRs. Participants at the workshop emphasized the fundamental differences between products that are generated to meet short-term needs (EDRs) and those for which consistency of processing and reprocessing over years to decades is an essential requirement. Climate research and monitoring often require the detection of very small changes against a naturally noisy background. For example, sea surface temperatures can vary by several degrees between daytime and nighttime, or from year to year, whereas the climate signal of interest may change by only 0.1 K over a decade. Moreover, changes in sensor performance or data-processing algorithms often introduce artificial noise that may be greater than the climate signal. In addition to natural and artificial noise, spatial and temporal biases in the measurements confound climate researchers. A CDR suitable for studying interannual to decadal climate variability and trends includes a time series produced with stable, high-quality data, and error characteristics that have been quantified by accounting for all of the above sources of error and noise. The production of a CDR requires considerable refinement of the raw data and the blending of multiple data streams. These streams may come from multiple copies of the same sensor, or they may be ancillary data fields that are used in synergy with the primary data stream.b Thorough analysis of sensor performance and improved processing algorithms are also required, as are quantitative estimates of spatial and temporal errors. Figure 2.1.1 illustrates the notional pathways that result in generation of an EDR and a CDR.c The past experience of the climate research community with the Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit (AMSU) provides a constructive case study in the challenges associated with constructing CDRs with satellite data. Starting in late 1978, nine polar-orbiting satellites carried identical copies of the MSU to measure atmospheric temperatures. In a 2000 National Research Council report,d it was noted that the last MSU occupied the afternoon orbit slot (NOAA-14), while the morning slot was monitored by the AMSU on NOAA-15.e Constructing CDRs from MSU instruments revealed that even though the prelaunch instruments were essentially identical, postlaunch differences among them were as large as the climate signal being sought. Once in space, each was found to have a unique response to variations in direct solar heating. Others experienced shifts in responses to onboard calibration targets. Another was found, after launch, to have been improperly calibrated in the laboratory. A final complication was due to the fact that the frequencies monitored with the new AMSU were slightly different from those monitored with the legacy MSUs. Scientists who were interested in stable, long-term temperature records from the MSU were required to commit considerable resources to discover the aforementioned problems and to test adjustments. A similar example is seen in the generation of sea surface temperature CDRs. Sea surface temperature (SST) CDRs were improved through several joint agency efforts (e.g., NOAA-NASA Pathfinder program) and,and, more recently, merging of complementary infrared and passive microwave satellite data having global daily coverage together with in situ observations as part of the international Global High Resolution SST Pilot Project (GHRSST-PP).f The GHRSST-PP is also pioneering the development of a high-resolution SST CDR within a dedicated reanalysis project, led by the NOAA’s National Oceanic Data Center, for the satellite era (1981-present). Calibration and validation in the context of CDRs can be considered a process that encompasses the entire system, from sensor to data product. The objective is to develop a quantitative understanding and characterization of the measurement system and its biases in time and space, which involves a wide range of strategies that depend on the type of sensor and data product.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report FIGURE 2.1.1 Pathways in the development of EDRs amd CDRs. SOURCE: J.J. Bates, NOAA National Climatic Data Center, “NPOESS EDRs vs. Climate Data Records (CDRs),” presentation to the Panel on Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft, April 23, 2007. a See National Research Council (NRC), Ensuring the Climate Record from the NPP and NPOESS Meteorological Satellites, National Academy Press, Washington, D.C., 2000, and NRC, Climate Data Records from Environmental Satellites: Interim Report, The National Academies Press, Washington, D.C., 2004. b Robust climate data records rely on the complementary nature of seemingly duplicate observations. For example, highly accurate and high-resolution infrared SST observations are confounded by the presence of clouds, whereas coarser-resolution passive microwave SST observations are able to measure SST through clouds. By combining synergistic use of the two data streams, the CDR can be improved. c From J.J. Bates, NOAA National Climatic Data Center, “NPOESS EDRs vs. Climate Data Records (CDRs),” presentation to the panel on April 23, 2007. d NRC, Ensuring the Climate Record from the NPP and NPOESS Meteorological Satellites, 2000. e NOAA 14 was decommissioned on May 23, 2007. f Proceedings from the Fourth GODAE High Resolution SST Pilot Project Workshop, Pasadena, Calif., Sept. 22-26, 2003. GHRSST-PP Report No. GHRSST/18 GODAE Report No. 10. Available at http://dup.esrin.esa.it/files/project/131-176-149-30_20068812258.pdf. More general information about GHRSST is available at http://www.ghrsst-pp.org.
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Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report Many participants noted that CDR science teams are crucial for maintaining the CDRs over many years (climate change time scales are long compared with those for weather), a task that is expected to require additional research, analysis, and validation of the observations (and thus funding, well beyond that applied to the EDRs). Prelaunch calibration and characterization that meet EDR requirements do not always (typically) meet the more exhaustive requirements for CDR accuracy and stability. Data-handling requirements are also completely different from those for EDRs and will likely require an independent CDR system. Whereas functionally the EDRs are short-lived operational products, the CDRs must be permanently stored and continuously accessible for considerable additional ongoing research and analysis if they are to be of use in climate change policy making and societal applications. Given that data requirements for CDRs can exceed those for EDRs, a list of missing data should be developed and considered as part of the mitigation option analysis. Participants also noted that where CDRs are particularly affected by the demanifesting of a sensor (e.g., APS), restoring the sensor without the capability for long-term CDR generation and maintenance is of little benefit. The workshop breakout session discussion specifically avoided defining agency roles and responsibilities, consistent with the workshop’s overall focus on identifying various options, but not their funding source. Further, the session participants suggested that the forthcoming National Research Council study on a strategy to mitigate the climate impacts that resulted from the NPOESS restructuring also avoid any attempt to assess costs or agency responsibilities, noting that these efforts should be initiated by the government in response to general study findings and recommendations regarding CDR generation requirements. Personnel training and maintenance of scientific capability over the long term were cited as essential elements of successful CDR development. It was noted that although operational programs also require skill continuity, the types and levels of skills required for CDRs are substantially more demanding and therefore more expensive to maintain than those for EDRs.