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This report provides a context in which questions put forth by NASA' s Office of Mission to Planet Earth (OMTPE) regarding the next steps in spaceborne synthetic aperture radar (SAR) science and technology can be addressed. It summarizes the state-of-the-art in theory, experimental design, technology, data analysis and utilization of SAR data for studies of the Earth, and describes potential new applications.
This report is divided into five science chapters and a technology assessment. The science chapters are Ecology, Hydrology, Marine Science and Applications, Ice Sheets and Glaciers, and Solid Earth Sciences and Topography. Each Chapter outlines key science questions in the context of Mission to Planet Earth that can be addressed with SAR data. In addition, the chapters summarize the value of existing SAR data and currently planned SAR systems, and identify gaps in observational capabilities that need to be filled to address the scientific questions. Both demonstrated and potential capabilities are described, with appropriate references cited. Both NASA and non-NASA sources of SAR data are included, and the importance of multiple wavelengths, multiple polarizations, and variable incidence angles are substantiated for each measurement. A summary of sensors is included as an Appendix. Cases where SAR provides complementary data to other (non-SAR) measurement techniques are also described.
The chapter on technology assessment outlines SAR technology development which is critical not only to NASA's providing societally relevant geophysical parameters, but to maintaining competitiveness in SAR technology, and promoting economic development.
SAR data provide unique information about the health of the planet and its biodiversity, as well as critical data for natural hazards and resource assessments. Interferometric measurement capabilities uniquely provided by SAR are required to generate global topographic maps, to monitor surface topographic change, and to monitor glacier ice velocity and ocean features. Multiparameter SAR data are crucial for accurate land cover classification, measuring above-ground woody plant biomass, delineation of wetland inundation, measurement of snow and soil moisture, characterization of oil slicks, and monitoring of sea ice thickness.
The suite of spaceborne SAR systems and programs currently envisioned by the international community provides an important framework for addressing key science issues and applications. However, additional activities, and interferometric/multiparameter measurement capabilities are required for long-term environmental monitoring and commercial applications.
This report recommends NASA take an aggressive leadership role in an international SAR program to meet these needs. Specific near-term steps should be to:
(1) Establish interagency and international SAR science teams. These teams would be funded to exploit data from both NASA and non-NASA sources, and would be charged with development and testing/validation of new applications, both scientific and commercial in nature.
(2) Initiate an advanced technology effort. The initial focus of such a program should be on lowering the costs of the operational elements and exploiting the functionality of SAR. The NASA airborne radar (AIRSAR) which flies on the NASA DC-8 should be the focus of this activity.
(3) Design an evolvable flight program. The long-term objective of such a program is an operational interferometric, multiparameter spaceborne SAR for long-term environmental monitoring and commercial applications. Immediate steps toward this goal are to initiate an interferometric spaceborne mission, and to continue multiparameter measurements through additional flights of the Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C/X-SAR) as a free-flyer or on the Space Shuttle.
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