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4 Opportunities in Satellite Remote Sensing to Realize the Vision Advances in remote sensing systems, data communications and processing technologies, and numerical models—including data-assimilation techniques—present a rich set of “push” opportunities for realizing the vision of the Earth Information System and associated enhanced weather and climate observations and predictions. A variety of advanced and complementary instruments on a constellation of satellites in different orbits (e.g., geostationary, polar and inclined low-Earth, highly elliptical or Molniya, and Sun-stationary), combined with ground-based, balloon, and aircraft in situ and remote sensing systems, will eventually form an intelligent sensor web. The data from this web can be continuously assimilated into high-resolution numerical models of the atmosphere. The observation and analysis process will yield a quasi-continuous digital representation of Earth on a global basis. This global database, which will include a complete and accurate representation of the atmosphere, ocean, and land and ice surfaces, is needed in order to enable much more accurate weather forecasts, to characterize the climate, and to advance understanding of the Earth system. This chapter describes some of the new and improved observations that are planned as part of future missions (Appendix C describes upcoming missions with U.S. involvement). Some of them are scheduled for transition into operations; others are not. Yet all of these planned observations and missions have the potential for eventual transition into operations and hence represent a plethora of “push” opportunities. Each of these opportunities can be identified and evaluated for transition potential, but each has its own transition pathway. Successful transition of these
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opportunities needs to be accompanied by supporting advances in infrastructure, including computers, communication technologies, and data-assimilation methods. This chapter is not meant to be a comprehensive description of all important technologies or missions. It concentrates on technologies and missions that are currently scheduled to be transitioned into operations or tested in real time in order to determine their impact on operations. ADVANCES IN SPACE-BASED MEASUREMENT TECHNOLOGIES New space-based remote sensing, communication, and processing technologies are being demonstrated through a number of research and development programs. The next-generation National Polar-orbiting Operational Environmental Satellite System (NPOESS), a joint program of the DOD, NOAA, and NASA, represents a giant step forward in global weather sensing capability. Imaging Fourier transform spectrometers, providing hyperspectral imagery of the atmosphere with unprecedented resolution, are being developed to observe the dynamics of the three-dimensional thermodynamic structure of the troposphere with high spatial and temporal resolution from geostationary satellites. Complementing these thermodynamic observations, a constellation of small, polar-orbiting satellites will retrieve thermodynamic profiles from the tracked GPS radio signals as they are occulted behind Earth’s limb. Doppler light detection and ranging systems, or lidars, which observe aerosol motion from the spectral frequency change of the backscattered light generated by a laser, are under development for polar-orbiting satellites in order to observe the global tropospheric wind structure. Scatterometers will provide surface wind data over the oceans. Lidars and radars will fly on low-altitude satellites for cloud, aerosol, and precipitation measurements, with the future possibility for high-vertical-resolution water vapor profiling. NPOESS will carry advanced instruments that detect the natural microwave radiation emitted by Earth’s surface and atmosphere. These instruments will enable atmospheric profiling through clouds and will provide surface wind and precipitation observations. Large, lightweight antenna systems are also under development, to enable similar microwave measurements from geostationary orbit for the monitoring of precipitation. These would also provide thermodynamic information below clouds in support of the infrared imaging spectrometer sounding systems. Dual-frequency radars will measure precipitation and associated latent heating rates. A visible-wavelength digital camera, which will sense lightning strokes, is also being developed to monitor convective storm dynamics from geostationary satellites. These new technologies (Kramer, 2001) are being developed during this decade through the U.S. New Millennium Program (NMP) and Earth System Science
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Pathfinder (ESSP) missions, the European Atmospheric Dynamics Mission (ADM), and the Japanese Advanced Earth Observation Satellite (ADEOS) program. ADVANCES IN SUPPORTING INFRASTRUCTURE The space-based observations from existing and planned missions will be voluminous, exceeding several terabytes per day. The observations will have both nowcasting and numerical weather prediction applications. As mentioned earlier, the full potential of many of these observations is not realized until they are assimilated in models along with other measurements. In order to take full advantage of all these data as well as to satisfy the diverse range of applications, an elaborate and highly efficient space-based communications system must be implemented. It is envisioned that before the end of this decade such a communications network will exist, to permit data to be transmitted around the globe to any desired location on Earth (Serafin et al., 2002). The products to be received and their frequency of receipt will depend only on the frequency and bandwidth of the ground-based receiver. The ground system will consist of both small, low-bandwidth receivers and larger, high-bandwidth receivers. The former will receive a limited number of products generated onboard spacecraft and intended for real-time strategic decisions. The latter will acquire the entire raw data stream, provided by the global observation system for numerical weather prediction, and will develop and distribute derived products to the user community. ADVANCES IN DATA PROCESSING AND ASSIMILATION Recent improvements in satellite data-assimilation techniques at modeling centers such as the National Centers for Environmental Prediction (NCEP) and the ECMWF have produced advances in numerical weather prediction as a result of improvements in the way these data are incorporated in the analysis/prediction operation. For example, the direct assimilation of satellite radiances, which represent volume-averaged temperature and moisture information rather than atmospheric soundings retrieved from the radiances, has led to a consistent, positive impact on the forecasts of these data in both hemispheres. Despite these promising trends, there remains an urgent need to continue developing better assimilation methods. These methods should be designed to effectively use the high spatial- and temporal-resolution satellite sounding observations that will be available operationally within the next decade. Rapidly increasing computer power is allowing for higher-resolution numerical models, which in turn demand data at higher spatial and temporal resolution in
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order to adequately describe the initial state of the atmosphere. Improved model physics is putting increased demands on data density and reliability. Advances in four-dimensional variational analyses (4DVAR) that can assimilate continuous data flow offer great hope for revolutionary improvements in the use of high-volume data sets. These advances will be coming from the new generation of satellite sounding instruments. The transitioning of such innovative observing technologies into operational applications must be rapid. Otherwise, the improvements in model forecasts that could come about with better observations will be slow to be realized. The time scale for the development of advanced satellite observing systems should be consistent with the evolving requirements and capabilities of numerical prediction models. Computer capability and numerical methods of data assimilation are evolutionary. As a consequence, the transition of new satellite technologies into the operational satellite systems must also be evolutionary, and designed to enable more frequent technology updates (i.e., “plug and play” modular satellite system designs, in which individual components have much shorter lifetimes than do current satellite instrument designs). Also, aggressive studies of satellite data assimilation and observing system simulation must be initiated well before the targeted launches of new observing capabilities if the numerical tools (i.e., radiative transfer models, expected error characterization, product development, and model initialization strategies) are to be in place when these new, advanced satellite data become available. PROGRAMS PROVIDING TRANSITION OPPORTUNITIES Existing programs within NASA and other agencies provide established and very rich sources of transition opportunities for NOAA operational programs. Current and planned missions within these programs can be readily evaluated for their transition potential, and in some cases they already have transition plans in place. National Polar-orbiting Operational Environmental Satellite System (NPOESS) The NPOESS program was instituted in 1994 as an interagency (NOAA, DOD, NASA) activity to merge the capabilities of the existing NOAA Polar-orbiting Operational Environmental Satellite (POES) program and DOD Defense Meteorological Satellite Program (DMSP). Over the past several years, the NPOESS program has established the requirements for and has begun the development of sensors to fly on the NPOESS satellites. The sensors are: Visible/Infrared Imager/Radiometer Suite (VIIRS)—VIIRS collects visible and infrared radiometric data from the atmosphere, ocean, and land surfaces.
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Cross-track Infrared Sounder (CrIS)—CrIS provides high-resolution measurements of the vertical distribution of atmospheric temperature, moisture, and pressure. Conical Microwave Imager/Sounder (CMIS)—CMIS provides microwave imagery and soundings of the atmosphere and oceans. Ozone Mapping and Profiler Suite (OMPS)—OMPS measures the vertical and horizontal distribution of ozone. Global Positioning System Occultation Sensor (GPSOS)—GPSOS measures the refraction of signals from the Global Positioning System and the Global Navigation Satellite System to characterize the ionosphere. Space Environment Sensor Suite (SESS)—SESS provides measurements of space environment variables, including particles, fields, and auroral conditions. Aerosol Polarimetry Sensor (APS)—APS measures characteristics of atmospheric aerosols. Each of these sensors represents a significant technological advance over predecessors on the POES and DMSP satellites (or, in the case of GPSOS and APS, other heritage systems), and the sensors have been developed largely through direct contracts with industry. The NPOESS program has an ongoing process to plan system improvements, including the development of new sensors to meet future NPOESS system needs. Geostationary Operational Environmental Satellite (GOES) System The Geostationary Operational Environmental Satellite (GOES) system consists of a series of geostationary satellites that provide high-temporal-resolution environmental measurements. Current GOES instruments include a visible/infrared imager, an infrared sounder, a solar x-ray imager, and a space environment monitor. The GOES spacecraft and sensors are procured from industry through contracts managed for NOAA by NASA. The specifications for new capabilities, technologies, and instruments are determined within the NASA GOES office at Goddard Space Flight Center (GSFC) in response to NOAA requirements and are implemented through contracts with industry. In some cases, sensors developed within NASA are specifically identified as candidates for transferring technology to the GOES program. The GOES program has formally maintained capacity to accommodate demonstration instruments funded from external sources, but the capacity has gone unused primarily because of the long lead times, lack of funding (including that for spacecraft integration), and absence of formal statements of operational requirements.
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Earth Observing System (EOS) and Post-EOS The NASA Earth Observing System (EOS) program, with its extensive set of research-oriented sensors on multiple satellites, has provided and will continue to provide an important source of technologies with strong potential for transitioning to operational use. Many of the sensors selected for flight on EOS missions were designed to provide data with long-term monitoring and climate research objectives. The Moderate-resolution Imaging Spectroradiometer (MODIS), currently flying on the EOS Terra and Aqua missions, is a multispectral imaging radiometer designed for imaging a variety of atmospheric, land, and ocean phenomena. This instrument provided the research basis for some of the requirements established for the NPOESS VIIRS sensor. The Atmospheric Infrared Radiation Sounder (AIRS) (Pagano et al., 2002), currently flying on the EOS Aqua satellite, initiated the new era of hyperspectral atmospheric sounders and is theoretically capable of measuring temperature and water vapor profiles with accuracies of 1 K and 15 percent, respectively, at a vertical resolution of approximately 1 km. AIRS, the forerunner of the NPOESS CrIS sensor, may provide a basis for future GOES sounders. The Global Precipitation Measurement (GPM) is a coordinated set of spacecraft planned to provide measurements of precipitation similar to those produced by the highly successful Tropical Rainfall Measuring Mission (TRMM), but with significantly higher revisiting time. To achieve this, it is planned that GPM will use a novel combination of a primary spacecraft with both a microwave radar and microwave radiometer and smaller secondary spacecraft carrying only radiometers. Earth System Science Pathfinder (ESSP) Program The NASA ESSP program funds missions designed to perform innovative and exploratory science. Measurements selected under ESSP often have significant operational potential, typically providing information on environmental variables that had not been previously measured from space. The Gravity and Climate Experiment (GRACE) was the first ESSP mission to be launched; it is currently providing detailed measurements of Earth’s gravity field. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) is a lidar mission designed to provide vertical profiles of clouds and aerosols. CloudSAT is a related mission that measures cloud profiles using a millimeter-wavelength radar. Both are expected to launch in 2004-2005. The Aquarius and Orbiting Carbon Observatory missions were selected in 2002 to provide measurements of ocean salinity and atmospheric carbon dioxide, respectively.
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New Millennium Program (NMP) The NASA NMP program was established to provide flight validation of new technologies. One mission, NMP Earth Observing (EO-1), has been launched and is operating successfully, with sensors designed to demonstrate technologies applicable to hyperspectral land imaging. A second mission, NMP EO-3, or GIFTS-IOMI (Geosynchronous Imaging Fourier Transform Spectrometer–Indian Ocean METOC [Meteorology and Oceanography] Imager), is currently under development in collaboration with NOAA and DOD; it is scheduled for launch in 2005. GIFTS will generate four-dimensional measurements of the atmosphere, providing more than 80,000 closely-spaced-horizontal (4 km), high-vertical-resolution (~1 km) temperature and moisture soundings every minute (Smith et al., 2002). NASA and NOAA expect GIFTS to provide candidate technologies for use in developing the next-generation GOES sounder. NPOESS Preparatory Project (NPP) The NASA NPOESS Preparatory Project (NPP) was established to bridge the gap between the expected operational life of the EOS Aqua satellite and the launch of the first operational satellites in the NPOESS series. It will also provide risk reduction of sensors scheduled for flight on the NPOESS satellites. NPP sensors include the VIIRS and CrIS instruments and the Advanced Technology Microwave Sounder (ATMS), being developed by NASA to transition the capability of the NASA Advanced Microwave Sounder Unit (AMSU) for use on NPOESS. NPP is expected to be a one-time project, but it is an excellent example of the use of “bridge” missions to transition research capability into operational systems. Other Programs A variety of other national and international programs provide valuable opportunities for the transition of research capabilities to operations. Relatively low cost, accurate, and high-vertical-resolution thermodynamic soundings of the atmosphere using radio occultation (RO) of GPS signals have been demonstrated on several missions (GPS/MET, Challenging Minisatellite Payload, and Satelite de Aplicaciones Coemtofocas-C). The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission (Anthes et al., 2000) plans to test in real time the impact of up to 3,000 global RO soundings daily with the launch of a constellation of six satellites in 2005. COSMIC is sponsored by the National Science Foundation (NSF), NASA, NOAA, DOD, and the National Space Program Office of Taiwan.
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Advances in lidar technologies provide a wide range of opportunities for new atmospheric measurement capabilities. In addition to the lidar technologies being developed for the Ice, Clouds, and Land Elevation Satellite (ICESat) and CALIPSO missions within the United States, the Atmospheric Laser Doppler Instrument (ALADIN), aboard the European Atmospheric Dynamics Mission, promises to advance the use of lidar for measuring tropospheric winds. Differential absorption lidar (DIAL) can enable the next advance, after that being achieved with high-resolution infrared spectrometers, for the profiling of water vapor as well as temperature. The use of passive microwave imaging sounders from geostationary orbit offers a promising new measurement capability. As with polar-orbiting systems, microwave sounders on geostationary satellites would complement existing infrared sounding sensors to provide temperature and moisture profiles through clouds and measurements of cloud liquid water and convective precipitation. ACHIEVING THE VISION OF THE EARTH INFORMATION SYSTEM As a result of the rapid advances in sensor, data processing, and communications technologies, the future is bright for space-based observing systems. New and improved sensors flown in a constellation of satellites in a variety of orbits will produce several terabytes of data per day. These data will be assimilated in numerical models—producing global analyses of the atmosphere, ocean, land surfaces, and cryosphere—advancing progress toward the Earth Information System. Communications and computing capacity are increasing at a rate that will accommodate this explosion of data. Emerging new information technologies, including new visualization tools, will be employed to enable effective human interpretation and use of the information. While it is an enormous task and challenge to assimilate the wealth of data to come from future satellite systems, the efficient conversion of these data into usable information remains the key for unlocking the still-unresolved mysteries of Earth’s environment and, ultimately, enabling its accurate prediction. The combination of new measurement technologies, enhancements in supporting infrastructure, and advances in data processing and assimilation provides the technological “push” for transitions. Existing programs within NASA and other agencies provide a rich but readily understood source of these opportunities. Achieving the vision of the Earth Information System requires efficient and effective processes for transitioning these coming technologies and capabilities into operational use.
Representative terms from entire chapter: