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2 Prioritization of Lost Capabilities and Options for Short-Term Recovery PRIORITIZATION PROCESS Each of the measurement capabilities that was lost or degraded following NPOESS and GOES-R program restructuring had been previously considered both practicable and of high importance. In the case of NPOESS, a tri-agency under-secretary-level executive committee provides overall program direction and ensures that both civil and national security requirements are satisfied.1 GOES-R requirements were established by NOAA following a formal process that determined and prioritized user requirements; various senior management committees oversaw this process.2 As is evident in the “highlights of analysis” sections in Chapter 3, the committee also found great merit in each of the climate-related measurement capabilities under consideration. However, given that a wholesale reversal of the programs’ changes is not feasible, it became the committee’s difficult task to provide a prioritized set of recommendations for restoration of measurement capabilities. In their request to the NRC, the study sponsors, NASA and NOAA, asked that a committee of the NRC “pri- oritize capabilities, especially those related to climate research, that were lost or placed at risk following recent changes to NPOESS and the GOES-R series of polar and geostationary environmental monitoring satellites” [emphasis added]. The committee understands “climate” to be “the statistical description in terms of the mean and variability of relevant measures of the atmosphere-ocean system over periods of time ranging from weeks to thousands or millions of years” (Climate Change Science Program and the Subcommittee on Global Change Research, 2003, p. 12). In the present study, the committee primarily considered climate-related physical, chemi- cal, and biological processes that vary on interannual to centennial timescales. It is also important to note that the committee did not a priori assume a longer-duration measurement record would be assigned a higher priority than a shorter-duration measurement record. Instead, the committee considered each measurement’s value to climate science in a more comprehensive sense as described below. The committee interprets the information needed for climate research broadly to be that which enables: • Detection of variations in climate (through long-term records), • Climate predictions and projections, and Presidential Decision Directive/NSTC-2, “Convergence of U.S.-Polar-Orbiting Operation Environmental Satellite Systems” May 5, 1994, 1 available at http://www.ipo.noaa.gov/About/NSTC-2.html. See Jim Gurka, “The Requirement Process in NOAA GOES-R Mission Definition,” April 12, 2007, available at http://osd.goes.noaa. 2 gov/documents/Requirements_Process.pdf. 7

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18 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT BOX 2.1 Goals of the U.S. Climate Change Science Program Goal 1: Improve knowledge of Earth’s past and present climate and environment, including its natural variability, and improve understanding of the causes of observed variability and change. Goal 2: Improve quantification of the forces bringing about changes in Earth’s climate and related sys- tems. Goal 3: Reduce uncertainty in projections of how Earth’s climate and related systems may change in the future. Goal 4: Understand the sensitivity and adaptability of different natural and managed ecosystems and hu- man systems to climate and related global changes. Goal 5: Explore the uses and identify the limits of evolving knowledge to manage risks and opportunities related to climate variability and change. SOURCE: The U.S. Climate Change Science Program Factsheet, available at http://www.climatescience.gov/infosheets/ factsheet3/CCSP-3-StratPlanOverview14jan2006.pdf. • Improved understanding of the physical, chemical, and biological processes that are involved in climate variability and change. In performing its prioritization, the committee was cognizant of the scientific importance of maintaining long- term records of forcing and improving understanding of the climate system through starting or continuing records of responses. It also recognized the challenges of finding an appropriate balance between observations of climate forcing and response, and between sustained observations and improved “process” understanding. The committee also notes that its interpretation of the research agenda for climate-related issues is consistent with the five goals of the U.S. Climate Change Science Program (Box 2.1). The prioritization exercise was conducted during a December 17-19, 2007, meeting of the committee. The exercise was guided by the following overarching principles: • The objective of the committee’s deliberations would be to prioritize restoration of climate capabilities. For example, a sensor with the capability to improve resolution of fast climate processes is of interest to both the weather forecast and climate research communities; however, it is the value to the latter that informs the committee’s ranking. • The particular recovery strategy and the cost of recovery of a measurement/sensor would not be a factor in the ranking.3 • Measurements/sensors on NPOESS would not be ranked against measurements/sensors on GOES-R; however, the criteria used in the ranking would be identical. • When it was relevant, judgments would be made according to the measurement objectives of a particular sensor, and not the sensor itself. Thus, for example, members of the committee considered the importance of ra- dar altimetry to climate science, rather than the importance of the particular implementation of this capability on NPOESS, that is, the ALT instrument. The committee did not have access to an ongoing NASA-NOAA study that is examining the costs of various recovery strategies. 3

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19 PRIORITIZATION OF LOST CAPABILITIES AND OPTIONS FOR SHORT-TERM RECOVERY Prior to the meeting, one or more committee members with the requisite expertise was assigned the task of preparing a detailed review of the issues associated with the descope or demanifest of a particular NPOESS or GOES-R measurement, guided by questions 1-9, below. These questions, which were developed at the committee’s first meeting, follow from the committee interpretation of climate science and the associated needs for climate observations (see above); they allow a prioritization across climate science’s various needs (for example, for long-term measurements, new measurements, measurements of climate forcings and responses, measurements to improve scientific understanding and reduce key uncertainties, and measurements to improve climate predictions). The questions are also consistent with the ranking criteria employed by the panels of the NRC Earth Science and Applications from Space decadal survey (NRC, 2007), although in that study societal benefits and cost consider- ations were included as ranking factors.4 By design, the questions were open-ended in order to provoke a more nuanced discussion of the value of the measurements. For example, rather than merely listing the duration of the measurement records at risk as a proxy for value, the committee considered the value of a long-term record in a more holistic manner via questions 1 and 5, which in turn prompted an in-depth exploration of the value of the long-term record, the impact of the record on global climate studies, the relative impact or consequences associated with a gap in the record, the maturity of related data assimilation, and sensor heritage. Such an analysis was considered important in the prioritization process in order to appropriately balance the needs to both continue very-long-duration measurements and pro- vide for shorter-duration measurements with high climate impact. The former would benefit with better scores for measurement/sensor maturity and the value of maintaining the long-term record. The latter measurements, although perhaps less mature, might result in greater consequences associated with a prospective measurement gap (for example, those related to climate forcing or response parameters with larger uncertainties for which longer trend data can greatly constrain future climate predictions). 1. To what extent are the data used both to monitor and to provide a historical record of the global climate? Is there a requirement for data continuity? If so, discuss the consequences of a measurement gap. 2. To what extent is this measurement important in reducing “uncertainty”—for example, in reducing error bars in climate sensitivity forcing and monitoring? In making these judgments, refer also to the priorities of the Climate Change Research Program. 3. Consider the importance of the measurement’s role in climate prediction and projections (forcing/response/sensitivity). 4. To what extent is the measurement needed for reanalysis? 5. Describe the measurement’s maturity—for example, its readiness to be assimilated into a particular model(s)—and its heritage. If discussing a sensor, discuss its technical maturity and heritage. 6. Are other sensors and ancillary data required to make the measurement useful? Is this measurement unique? Are there complementary international sensors? If so, please list them and assess their capabilities. Discuss any data issues you may be aware of. 7. To what extent are the data used by, for example, the Intergovernmental Panel on Climate Change and the Climate Change Science Program (in developing synthesis and assessment products)? 8. Provide a qualitative assessment of the measurement’s role in contributing to an overall improved under- standing of the climate system and climate processes. 9. To what extent does the measurement contribute to improved understanding in related disciplines? Following each reviewer presentation, committee members actively discussed each of the nine questions for the measurement need under consideration. Each committee member who was present then entered a numerical score from 1 (highest priority) to 5 (lowest priority) on a scorecard. After the final presentation, the scorecards were submitted and the results tallied. The committee’s prioritization resulted from numerical scoring of the im- portance of these factors for the needs of the climate research community (questions -8) and the importance of See Box 2.2 in Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (NRC, 2007), p. 40. 4

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20 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT the measurement to related disciplines (question 9). Each of the responses to questions -9 was given equal weight in determining an overall ranking.5 The committee had extensive discussions on whether a simple average of member rankings of the responses to Questions 1-9 should be used for an overall ranking, or whether rankings of particular questions should be given more weight. In part because there was no consensus among committee members on how a particular weighting scheme might improve what was already a subjective evaluation (mapping study statement of task to the questions; individual numerical rankings for each question), the committee determined that the use of an unweighted average was advisable. Further, as the committee was not provided any information concerning costs, relative or absolute, for any of the proposed mitigations, prioritization was based entirely on climate science value as determined by consideration of the nine questions above. The committee notes, however, that had costs been provided, a more far-reaching set of recommendations might have been developed in which cost/benefit was taken into consider- ation. Finally, it is important to recognize that important non-scientific factors were, by design, not part of the committee’s analysis. Climate Areas Impacted by NPOESS Changes The committee considered the climate-related impacts of descopes to the NPOESS and GOES-R programs in a thematic context. For NPOESS, the committee considered: • Aerosol properties and the Aerosol Polarimetry Sensor (APS), • Earth radiation budget and the Clouds and Earth’s Radiant Energy System/Earth Radiation Budget Sensor (CERES/ERBS), • Hyperspectral diurnal coverage and the Cross-track Infrared Sounder (CrIS), • Microwave radiometry and the Conical Scanning Microwave Imager/Sounder (CMIS), • Ocean color and the Visible/Infrared Imager/Radiometer Suite (VIIRS) sensor, • Ozone profiles and the Ozone Mapping and Profiler Suite-Limb (OMPS-L) sensor, • Radar altimetry and the ALT sensor, and • Total solar irradiance and the Total Solar Irradiance Monitor (TIM); spectrally resolved irradiance and the Solar Spectral Irradiance Monitor (SIM). For GOES-R, the committee considered: • Geostationary Hyperspectral Sounding and the HES sensor, and • Coastal waters imagery and the HES-CWI sensor. The climate capability areas considered for prioritization are briefly described here (in alphabetical order), and are discussed in more detail in dedicated sections in Chapter 3. Aerosol Properties Tropospheric aerosols play a crucial role in climate and can cause a climate forcing directly by absorbing and reflecting sunlight, thereby cooling or heating the atmosphere, and indirectly by modifying cloud properties. The Aerosol Polarimetry Sensor (APS), eliminated following Nunn-McCurdy certification but originally planned to be included on the first and fourth NPOESS spacecraft, was intended to (1) measure the global distribution of natural and anthropogenic aerosols (e.g., black carbons, sulfates) with accuracy and coverage sufficient for reli- able quantification of the effect of aerosols on climate, the anthropogenic component of the aerosol effect, and the The committee was aware of a similar prioritization exercise that had been conducted by NASA and NOAA in late 2006/early 2007. NASA 5 and NOAA reached a somewhat different prioritization, which we attribute in large part to their giving additional weight to the factors noted in question 1, that is, measurement continuity and the importance of avoiding a data gap.

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21 PRIORITIZATION OF LOST CAPABILITIES AND OPTIONS FOR SHORT-TERM RECOVERY potential secular trends in the aerosol effect caused by natural and anthropogenic factors; (2) measure the direct impact of aerosols on the radiation budget and its natural and anthropogenic components; (3) measure the effect of aerosols on clouds (lifetime, microphysics, and precipitation) and its natural and anthropogenic components; and (4) investigate the feasibility of improved techniques for the measurement of black carbon and dust absorption to provide more accurate estimates of their contribution to the climate forcing function.6 The committee considered the originally planned measurements to determine relative prioritization of this lost climate measurement capability. Earth’s Radiation Budget Along with incoming solar radiation, outgoing radiation helps establish Earth’s radiant energy balance; the difference between the two corresponds to “climate forcing,” which is exhibited in part by rising global average tropospheric temperatures. The CERES and ERBS sensors, which measure outgoing radiation, were designed to continue a data record from 1984 that is providing information on how energy from the Sun is absorbed and re-emitted by Earth, including the effects of human activities (such as the burning of fossil fuels and the use of chlorofluorocarbons) and natural occurrences (such as volcanic eruptions). These measurements are currently provided by the CERES instruments on the TRMM (1997), Terra (1999), and Aqua (2002) missions. 7 Prior to the Nunn-McCurdy certification, the NPOESS program planned to place the last remaining CERES sensor, a flight spare from TRMM designated as FM-5, on the first NPOESS 13:30 orbit, with a launch in 2010, and then place ERBS on NPOESS C4 in 2015 and beyond. Following certification, the CERES FM-5 instrument was retained for NPOESS C1, which is now planned for launch in 2013, and all subsequent ERBS instruments were demanifested. 8 The committee considered the originally planned measurements to determine a relative prioritization of this lost climate measurement capability. Hyperspectral Diurnal Coverage The Cross-track Infrared Sounder (CrIS) is an interferometric sounding sensor designed to measure upwelling Earth radiances at very high spectral resolution. Data from CrIS and another NPOESS sensor, ATMS (Advanced Technology Microwave Sounder), are used to construct vertical profiles of atmospheric temperature, moisture, and pressure. The certified NPOESS deletes CrIS and ATMS from the early AM (05:30 local solar time) orbit platforms, but retains the sensors on the PM orbit platforms (C1, launching in 2013, and C3, launching no earlier than 2018). The committee considered the importance of additional diurnal coverage to determine relative priori- tization of this degraded climate capability. Microwave Radiometry The Conical Scanning Microwave Imager/Sounder (CMIS) sensor was canceled following NPOESS certifica- tion; it is in the process of being re-competed as a similar but less capable, less expensive, and less technologically risky sensor, designated MIS (Microwave Imager/Sounder). Prior to certification, CMIS was baselined for inclusion on each of the six NPOESS spacecraft, starting with C1 in 2010. Post-certification, CMIS is delayed until launch of the second NPOESS spacecraft, now scheduled for no earlier than 2016. CMIS/MIS will provide global micro- wave radiometry and sounding data to produce microwave imagery and other meteorological and oceanographic data. Data types include atmospheric temperature and moisture profiles, clouds, sea surface vector winds, and APS is an instrument on the Glory spacecraft. Its measurement objectives can be found on the Glory homepage at http://glory.gsfc.nasa. 6 gov/overview-aps.html. CERES (Clouds and Earth’s Radiant Energy System) consists of two broadband scanning radiometers that measure Earth’s radiation balance 7 and provide cloud property estimates to assess their role in radiative fluxes from the surface to the top of the atmosphere. See http://science. larc.nasa.gov/ceres/index.html. As this report went to press, additional delay (from 2009 to mid-2010) in the launch of the NPOESS Preparatory Project spacecraft was 8 announced. To avoid a potential gap in Earth radiation budget measurements, NASA and NOAA officials were planning to move CERES FM-5 to the NPP platform from NPOESS C1.

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22 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT all-weather land/water surfaces. The original CMIS was planned to contribute to 23 NPOESS environmental data records (EDRs) and was the primary instrument for nine EDRs. As noted, the reduced-capability MIS sensor will not be available for the first NPOESS platform. The committee considered the multitude of climate community microwave radiometry needs to determine relative prioritization of the likely measurement gap associated with deferral of this climate capability until the launch of NPOESS C2. Ocean Color The Visible/Infrared Imager/Radiometer Suite (VIIRS) will collect visible/infrared imagery and radiometric data (Lee et al., 2006). VIIRS will combine the radiometric accuracy of the Advanced Very High Resolution Radi- ometer (AVHRR) currently flown on the NOAA polar orbiters with the high spatial resolution of the Operational Linescan System (OLS) flown on the Air Force’s Defense Meteorological Satellite Program (DMSP) spacecraft. The VIIRS instrument that is planned for launch on the NPP spacecraft is now considered unlikely to meet its design requirements for measurements of ocean color given that recent instrument tests show higher than antici- pated optical cross-talk that will degrade instrument performance. Ocean color measurements are used to detect and monitor changes in water quality and ocean primary productivity, track harmful algal blooms, and assess underwater visibility for divers; they are also used in a variety of other applications related to ocean ecosystems, carbon and elemental cycling, coastal habitats, and coastal hazards (Siegel and Yoder, 2007; see Appendix C). The committee considered the impacts of the VIIRS sensor’s degraded performance on ocean-color-related data products and prioritized the importance of restoring the degraded capabilities according to the climate-focused criteria enumerated above. Ozone Profiles The OMPS-Limb sensor, now demanifested from NPOESS, was to provide measurements of ozone vertical profiles, which are needed to understand and monitor the processes involved in the depletion and anticipated re- covery of ozone in the stratosphere. Certification made no change to the OMPS-Nadir instrument, which measures total column ozone at nadir and continues the record from TOMS. The committee considered the originally planned OMPS-Limb measurements to determine relative prioritization of this lost climate capability. Radar Altimetry Because of the expense and the logistical and operational difficulties of obtaining globally distributed in situ oceanic observations, altimetry has been identified as the central element of major programs aimed at understand- ing the ocean’s role in climate.9 The ALT instrument, demanifested from NPOESS following certification, was originally planned for flight on NPOESS C2 and C5. Prior to its elimination from NPOESS, data from ALT was planned to continue an unbroken record first established with the launch in 1992 of the TOPEX/Poseidon mission. This record was maintained with the launch of Jason-1 in 2001, and will continue with the launch of the Ocean Surface Topography Mission, also known as Jason-2, in 2008. However, as emphasized by many participants at the June 2007 workshop, the inclusion of ALT on NPOESS platforms, all of which will be in Sun-synchronous orbits, would likely prevent it from being able to provide data of the quality desired by the climate community. 10 The committee thus considered the climate community’s need for climate-quality precision radar altimetry mea- surements to determine relative prioritization of this lost climate capability. For example, the World Ocean Circulation Experiment (WOCE) and the Climate Variability and Predictability (CLIVAR) program of the 9 World Climate Research Programme (WCRP). See “Report of the Altimeter Study Group to NASA Headquarters and the EOS Payload Panel,” The Earth Observer, January/February, Vol. 7 No. 1, 1995. Available at http://eospso.gsfc.nasa.gov/eos_observ/1_2_95/p03.html. To compute ocean circulation from sea surface topography, the tidal component from the observed sea surface height must be subtracted, 10 as even the best models of ocean tides have errors. ALT measurements from the NPOESS Sun-synchronous orbit would inherently be subject to aliasing from tidal activity, and thus inadequate to continue the precision altimetry record.

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23 PRIORITIZATION OF LOST CAPABILITIES AND OPTIONS FOR SHORT-TERM RECOVERY Total Solar Irradiance TSIS consists of a total solar irradiance monitor (TIM) plus a solar spectral irradiance monitor (SIM). The TIM portion measures total solar irradiance (TSI), the integrated solar radiation incident at the top of Earth’s at- mosphere, in order to continue a climate record, unbroken since 1978, that is used to determine the sensitivity of Earth’s climate to the natural effects of solar forcing. SIM continues the recently established, and thus relatively shorter, record of solar spectral irradiance (SSI) begun by SORCE (2002-). Prior to Nunn-McCurdy, TSIS was planned to fly on the original NPOESS early AM platforms C2 (2011) and C4 (2014). Nunn-McCurdy certifica- tion resulted in the demanifest of TSIS from NPOESS. The committee considered both TSI and SSI measurement needs to determine relative prioritization of this lost climate capability. Climate Areas Impacted by GOES-R Changes Coastal Waters Imagery The coastal waters region is frequently defined as the 400 km zone adjacent to the continental United States. These waters are highly dynamic: tides, diurnal winds, river runoff, upwelling, and storm winds drive currents that range from 1 to approximately 3 m/s. Three-hour or better sampling is required to resolve these features and to track red tides, oil spills, or other features of concern for coastal environmental management. The Coastal Water Imager (CWI) was a proposed component of the Hyperspectral Environmental Suite (HES) that would be flown on the Geostationary Operational Environmental Satellite R Series (GOES-R) to acquire multispectral to hyper- spectral visible/near-infrared images of Earth’s surface at high spatial and temporal resolution. Its data would fill an existing gap in the time-space domain of available observations obtained from existing spaceborne sensors. The HES-CWI instrument was demanifested from GOES-R as a result of decisions announced in September 2006. The committee considered the originally planned coastal waters measurements to determine relative prioritization of this lost climate capability. Geostationary Hyperspectral Sounding Operational high-spectral-resolution infrared radiance measurements from the geostationary perspective were to be introduced on GOES-R with the HES (Hyperspectral Environmental Suite). The advanced hyperspectral sounder was planned to have more than 1,000 channels with narrow spectral widths compared to the current GOES sounders, which have only 18 much wider bands. In turn, HES would have provided substantially improved temperature and water vapor vertical profiles with higher accuracy and vertical resolution than are available with current sounder technologies. As noted above, the HES instrument was demanifested from GOES-R; the committee considered the originally planned geostationary hyperspectral measurements to determine relative prioritization of this lost climate capability. NEAR-TERM MITIGATION OPTIONS The following sections summarize the committee’s analysis of near-term recovery and mitigation options for the climate-related measurements and associated sensors that were impacted by the changes following Nunn-Mc- Curdy certification and the cancelation of HES on GOES-R. It is important to note that the committee considered a range of options and did not limit its analysis to the practicality of simply restoring a demanifested or descoped sensor. The options studied included reintegration on NPOESS or GOES-R platforms, free-flyer missions, flights of opportunity, and leveraging international efforts. Because of the limitations noted above, the depth of the committee’s analysis varies. The committee also emphasizes that the options discussed below are effectively only a first step—a necessary but far from sufficient condition—in establishing a viable long-term climate strategy.

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24 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT Reintegration on NPOESS Platforms The committee was briefed on the agencies’ proposed strategy to recover climate capabilities lost as a result of the NPOESS Nunn-McCurdy descoping. The proposed strategy centered heavily on the formation of a new series of free-flyer missions rather than restoration of the appropriate sensors to the NPOESS platforms. The high cost of reintegration and risk to NPOESS launch schedules were cited as the primary reasons for this approach. It is somewhat surprising to the committee that the cost of reintegration is at issue, given that the satellites themselves were expressly designed to support the original payload suite and have not been descoped. 11 While a dedicated line of free-flyer climate satellites is clearly attractive for its gap-filling capability and singular focus on climate needs, the committee is not convinced that the strategy put forth by the agencies adequately meets the breadth of needs of the climate science community, nor does it appear to be a cost-effective approach. The ef- ficiency of establishing a new line of climate satellites versus restoration of certain sensors to NPOESS demands further consideration. Free-Flyer Missions As noted in the report from the June 2007 workshop (NRC, 2008a, p. 45): The use of free-flying spacecraft to ensure the continuity of CDRs [climate data records] was frequently suggested as desirable by workshop participants. Free flyers provide increased launch flexibility, which decreases the risk of a gap in the measurements. It was considered noteworthy that none of the climate sensors are considered of sufficiently high priority for sensor failure to trigger the launch of a new NPOESS bus to preserve the data record. However, free flyers are not without risk, as they are typically more susceptible to cancellation compared with a single large, operational spacecraft bus. Some participants also noted that regardless of their desirability, NOAA has no history of utilizing free flyers as operational space platforms. The use of smaller, comparatively less expensive platforms may facilitate technology insertion into an op- erational program. Free flyers also allow a spacecraft’s orbit to be tailored to the requirements of a particular observation; however, in the very constrained budgetary environment that is anticipated for the foreseeable future, expenditures for free flyers might also have to compete against resources to implement the decadal survey mission recommendations (NRC, 2007). The decadal survey missions represent a set of community consensus priorities spanning Earth science including, but not limited to, climate science. Mitigation strategies presented here were considered entirely within the context of climate measurement recovery, and are not to be construed as a review of decadal survey mission priorities. In order to support requirements for near-simultaneous observations, a free-flyer architecture might neces- sitate launching multiple spacecraft into a closely spaced formation. The principal benefit of formation flying is the ability to combine multiple, synergistic measurement types without incurring the cost, complexity, and risk of large facility-class observatories. There are, of course, operational challenges associated with formation flight (for example, maneuver coordination, orbit insertion, and end-of-life considerations), although these can be addressed through careful plans and procedures, and through taking advantage of the lessons learned through NASA’s A-train12 operations (Box 2.2). The opportunity for free flyers to orbit in formation, for example, with the NPOESS or the MetOp series, would provide greatly added flexibility to recover climate measurement capabili- ties for sensors that require co-aligned observations from other NPOESS sensors (e.g., ERBS requires ancillary NPOESS satellite bus capabilities were not descoped as part of Nunn-McCurdy certification and the recertified program retained funding 11 within the NPOESS baseline for the reintegration of the demanifested sensors should a way be found to provide them from outside the program. See, for example, Statement of Dr. John Marburger, III, Director, Office of Science and Technology Policy, to the Committee on Science and Technology Subcommittee on Energy and Environment, United States House of Representatives, “Status Report on the NPOESS Weather Satellites,” June 7, 2007. Available at http://science.house.gov/publications/Testimony.aspx?TID=6519. The “A-Train” satellite constellation consists of two of the major EOS missions, three ESSP missions, and a French Centre National d’Etudes 12 Spatiales (CNES) mission flying in close proximity. See http://aqua.nasa.gov/doc/pubs/A-Train_Fact_sheet.pdf.

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25 PRIORITIZATION OF LOST CAPABILITIES AND OPTIONS FOR SHORT-TERM RECOVERY BOX 2.2 Formation Flight: The A-Train Achieving formation flight with a diverse set of spacecraft, including the large EOS observatories, micro- satellites, and international partner satellites—some launched years apart—required advances in both station-keeping ability and operational coordination. The ability to station-keep multiple satellites in their assigned boxes within the train—including satisfaction of footprint overlap requirements—is now operation- ally demonstrated. In September 2004, NASA published the “Afternoon Constellation Operations Coordina- tion Plan,” jointly written by all of the Constellation members to keep the A-Train Constellation (Figure 2.2.1) organized and safe.1 To perform independent and coordinated measurements and thereby derive greater science value than that possible from the individual missions alone, each satellite operator must know the trajectory and mission operations plans for the other missions. In formation flying, the relative accelera- tion between satellites is estimated and used to plan maneuvers to give one satellite (e.g., CloudSat) the desired motion relative to another (e.g., CALIPSO).2 Drag-make-up and inclination maneuvers must also be effected, as well as coping with anomalous situations. FIGURE 2.2.1 The A-Train, on-orbit today, including the future OCO mission. SOURCE: Courtesy of NASA. 2.2.1.eps There are many advantages of formation flight: • The degree of simultaneity can be assigned based upon position within the formation. • The formation can be permanent, with its composition changing over time. • International cooperation is facilitated. • Technology insertion is facilitated. • Individual sensor replacement is facilitated. • Synergies can be achieved. The A-Train was formed around the large EOS Aqua and Aura observatories. In the NPOESS era, such trains might be centered around the NPP, MetOp, and NPOESS spacecraft—and lower-inclination missions. Standard buses capable of carrying several instruments, which exist in spacecraft catalogs, can readily accommodate various combinations of operational weather and climate instruments. Afternoon Constellation Operations Coordination Plan, prepared by Angelita C. Kelly/GSFC Constellation Team 1 Manager, Ron Boain/JPL CloudSat Project Engineer, Karen Richon/GSFC ESMO Constellation Flight Dynamics Lead, and Mary Elizabeth Wusk/LaRC CALIPSO Ground System Manager, Earth Science Mission Operations Project, NASA/ GSFC, September 2004. D.E. Keenan, A Formation Flying Strategy for CloudSat/Picasso-Cena (CALIPSO), IEEE Proceedings 2:535-552, 2 2001.

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26 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT data from a multispectral imager such as VIIRS). With attention to the requisite orbit maintenance and operations requirements, NASA and NOAA should be able to include formation flying as a deliberate part of a mitigation strategy for restoring NPOESS and GOES-R climate-observing capabilities. Flights of Opportunity In some cases, sensors can be manifested on already-planned missions to capitalize on surplus satellite per- formance capability. Flights of opportunity might leverage planned NASA or NOAA missions, or take advantage of so-called secondary-payload capability on planned commercial flights. Repeated commercial flights, such as those of Intelsat (GEO) and Iridium NEXT (LEO), offer potential opportunities for one-of-a-kind or extended lines of climate instruments to be flown at negotiated costs. Each platform will bring its own electromagnetic interference environment, pointing control and knowledge capabilities, and accommodation parameters. And each provider will have tight timelines, presenting a challenge to government programs when decision making and procurement occur over years, rather than months. However, these opportunities can provide cost-effective mechanisms for access to space for appropriate climate sensors and measurements, and should be considered. Leveraging International Efforts The committee recognizes the value of bilateral and multilateral cooperation among space agencies; notable examples include TRMM, Jason, and the planned GPM and JPS constellations. 13 The committee also notes the value of various international planned activities and their potential contributions to better understanding of climate and its impacts, such as the European Sentinel-1, 2, and 3 missions that support the European Union and its Member States’ operational services for Global Monitoring for Environmental Security (GMES). 14 Other future satellite missions under ESA’s Living Planet Programme—for example, GOCE, SMOS, ADM, and CryoSat-2—will support the GMES program and also provide valuable information for understanding and assessing Earth’s climate system. The committee supports continued efforts to coordinate and strengthen international partnerships so as to ensure provision of key climate science measurements, and it recognizes the growing importance of such collaboration as budgets are increasingly stretched to accommodate the variety of stakeholder needs for Earth system data.15 However, large uncertainties are also associated with attempts to factor international partner missions into the timing of U.S. missions, including the obvious potential for pro- gram changes and continuing concerns about access to data, full participation in science teams, and difficulties related to restrictions associated with International Traffic in Arms Regulations (ITAR). 16 This is especially true for emerging international space programs (e.g., in China). In November 1998, NOAA entered into an agreement with the European Organisation for the Exploitation of Meteorological Satellites 13 (EUMETSAT) to participate in the Initial Joint Polar-orbiting Satellite system (IJPS). The agreement calls for cooperation between NOAA and EUMETSAT to provide meteorological data for “morning” and “afternoon” orbits by complementing each other’s polar satellite global coverage. Under this agreement NOAA will also provide some of the instruments on-board the EUMETSAT satellites (http://projects.osd.noaa. gov/IJPS/mission.htm). In June 2003, NOAA and EUMETSAT signed the Joint Transition Activities Agreement that will allow EUMETSAT and the United States continued access to environmental data collected by each other’s satellites and calls for the parties to begin preparing for a future joint polar system (JPS) post 2020. The first MetOp satellite launched in late 2006. The GMES Space Component program includes the following instruments or sensing capabilities, which are grouped into “Sentinels”: 14 Sentinel-1, a C-band interferometric radar mission; Sentinel-2, a multispectral optical imaging mission; and Sentinel-3, a mission with wide- swath low-medium resolution optical and infrared radiometers and a radar altimeter package. On the role of international partners in future Earth observation missions, see also Chapter 3, “From Satellite Observations to Earth Infor- 15 mation,” in Earth Science and Applications from Space (NRC, 2007). Concerns about ITAR restrictions were discussed during the June 2007 workshop. A recent NRC report examines these issues in detail 16 (NRC, 2008b).

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27 PRIORITIZATION OF LOST CAPABILITIES AND OPTIONS FOR SHORT-TERM RECOVERY SUMMARY OF PRIORITIES While the committee found merit in all of the climate capabilities considered, it also recognized that absent sufficient resources, difficult choices would have to be made. Therefore, rather than recommending a wholesale restoration of all lost capabilities, the committee set out to provide a prioritized set of specific recommendations. Because the committee was not given any information concerning costs, relative or absolute, for any of the pro- posed mitigations, prioritization was based entirely on climate science merit. The committee notes, however, that had costs been provided, a more far-reaching set of recommendations might have been developed in which relative cost/benefit was taken into consideration. As noted above, the committee prioritized the entire list of lost or diminished climate-related capabilities rather than limiting its recommendation to the demanifested sensors, as was done in the NASA-NOAA “remanifesting” study for the Office of Science and Technology Policy (OSTP). When interpreting the committee’s findings, it is also important to recognize that the committee considered the importance of the duration of a measurement’s record in the overall context of the measurement’s value to climate science. This methodology appears to differ from that employed by the NASA-NOAA remanifesting study, which, by design, had as its primary objective to “ensure continuity of long-term records.”17 The committee’s approach is consistent with input received from the community as part of the June 2007 workshop. Based on the results of the prioritization process, the committee found four natural groupings in its scoring prioritization (Figure 2.1), which are designated in descending order of priority as Tier 1 through Tier 4; a simplified version of these results is shown in Table 2.1. Within each group, the committee then considered each capability individually to provide recommended short- and long-term recovery strategies. Although the same nine questions were used to analyze the relative climate science impact of both GOES-R and NPOESS descopes in GEO and LEO orbits, respectively, sensors from the different programs were not prioritized head-to-head. However, it can be stated roughly that, considering climate science contributions alone, the recommendations regarding geostationary hyperspectral sounding compare to the Tier 2 LEO capability prioritization, and coastal waters imagery falls into Tier 4. Prioritization of climate capabilities, although considered in the context of NPOESS and GOES-R program- matic changes, does not in all cases result in a recommendation for restoration of the originally planned sensors. Indeed, in the case of ALT, restoration of the original sensor to the NPOESS platform does not address the climate need for radar altimetry; yet provision of climate-quality radar altimetry is one of the highest-priority capabilities. Thus, as a recovery strategy the committee recommends a series of precision altimetry free flyers, rather than restoration of ALT to the NPOESS platforms. REFERENCES Climate Change Science Program and the Subcommittee on Global Change Research. 2003. Strategic Plan for the U.S. Climate Change Science Program. Available at http://www.climatescience.gov/Library/stratplan2003/final/default.htm. Lee, T.E., S.D. Miller, F.J. Turk, C. Schueler, R. Julian, S. Deyo, P. Dills, and S. Wang. 2006. The NPOESS VIIRS Day/Night Visible Sensor. Bull. Amer. Meteor. Soc. 87:191-199. Available at http://npoess.noaa.gov/News/Archive/2006/apr/01/BAMS_FEB2006.pdf. NRC (National Research Council). 2007. Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. The National Academies Press, Washington, D.C. NRC. 2008a. Options to Ensure the Climate Record from the NPOESS and GOES-R Spacecraft: A Workshop Report. The National Academies Press, Washington, D.C. NRC. 2008b. Space Science and the International Traffic in Arms Regulations: Summary of a Workshop. The National Academies Press, Washington, D.C. Siegel, D., and J. Yoder. 2007. “Community Letter to NASA and NOAA Regarding Concerns Over NPOESS Preparatory Project VIIRS Sen- sor,” letter to M. Griffin and VAdm. Lautenbacher, October 2, 2007. Available at http://www.spaceref.com/news/viewsr.html?pid=25593 and in Appendix C of this report. Bryant Cramer, “Mitigation Approaches to Address Impacts of NPOESS Nunn-McCurdy Certification on Joint NASA-NOAA Climate 17 Goals: Joint NASA-NOAA Study for OSTP (Phase II),” June 19, 2007, available at http://www7.nationalacademies.org/ssb/NPOESSWork- shop_Cramer_NRC_06_19_07_final.pdf and also reprinted in Appendix C of the June 2007 workshop report.

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28 ENSURING THE CLIMATE RECORD FROM THE NPOESS AND GOES-R SPACECRAFT FIGURE 2.1 Graphical depiction of overall rankings, showing the clustering of scores into what the committee defined as Tiers 1-4, for recovery of both NPOESS (low Earth orbit) and GOES-R (geostationary Earth orbit) lost or degraded climate capabilities. TABLE 2.1 Relative Prioritization for the Mitigation of Lost or Degraded Climate Capabilities Lost or Degraded Climate Capability Lost or Degraded Climate Capability in NPOESS Low Earth Orbit in GOES-R Geostationary Earth Orbit Tier 1 Microwave Radiometry Radar Altimetry Earth Radiation Budget Tier 2 Hyperspectral Diurnal Coverage Geostationary Hyperspectral Sounding Total Solar Irradiance Tier 3 Aerosol Properties Ocean Color Ozone Profiles Tier 4 Geostationary Coastal Waters Imagery