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DEVELOPMENT AND APPLICATION OF SMALL SPACEBORNE SYNTHETIC APERTURE RADARS
The committee notes that of the several proposed operating frequencies associated with SARs, the L-band is especially useful in forest and desert ecology applications, but other applications such as agriculture may lead to a small SAR design based on C-, X-, or Ku-band frequencies. These frequencies require smaller antennas than does the L-band, which may simplify deployment from a small spacecraft. In the committee's view, design parameters such as frequency, polarization, resolution, and swath width should be chosen to match the mission focus, while the results of all available research, including that from the 1960s and 1970s, are considered.
Adopt new technologies to reduce SAR costs.
In the committee's view, many new technologies may come from outside NASA. In addition, new technologies currently available for data capture and processing can be used to lower overall SAR system costs. Many of these technologies can be evaluated without resorting to costly spacecraft missions. According to JPL's LightSAR point design report (JPL, 1997), the estimated end-to-end mission cost of the baseline design is $125 million, which is only a fraction of the estimated mission costs of the single-frequency, single-polarization SARs of ERS-1 ($750 million) and Radarsat ($640 million). The significant reduction in cost is attributed to the incorporation of new technologies. As examples of cost-reducing technologies, L-band antennas are seven times lighter and require only half as much power as SIR-C's antenna. Small SAR synthesizers are seven times lighter than SIR-C's and require one-tenth the power.
Continue support of a vigorous research and analysis program in radarremote sensing.
Although considerable progress has been made in recent years, there are many areas in which understanding of the physical link between the SAR signal and the geophysical phenomenon is weak. For example, there is a strong soil-moisture signal present in certain SAR imagery, but more research is necessary to learn how to quantify the effects of surface roughness and vegetation on soil-moisture signals. NASA should continue appropriate studies to strengthen these links. These studies may involve theory, ground-based scatterometers, and aircraft SARs. Such calibration and validation studies should also be an integral part of any small SAR mission.
Establish a clearly defined small SAR data policy that will protectcommercial interests while ensuring free and open access by the publicand research communities.
SAR imagery has potentially important applications for research, the public sector, and commercial users. If NASA continues to seek commercial partners for a small SAR mission (to reduce costs), it must define data policies clearly to protect the proprietary interests of commercial entities while ensuring open access to other user communities. In addition, widely distributed data processing and dissemination may both lower costs and increase access to small SAR data. Such a “federated” approach is consistent with the strategy being pursued for the Earth Observing System Data and Information System (EOSDIS).
It is expected that much data will be dual-use in nature and can serve multiple interests (science, public use, and commerce). Innovative data access policies could protect both research and commercial communities. For example, most commercial applications may have a relatively