A space-based synthetic aperture radar (SAR) designed to provide quantitative information on a global scale implies severe
requirements to maximize coverage and to sustain reliable operational calibration. These requirements are best served by the
hybrid-polarity architecture, in which the radar transmits in circular polarization, and receives on two orthogonal linear
polarizations, coherently, retaining their relative phase. This paper summarizes key attributes of hybrid-polarity dual- and
quadrature-polarized SARs, reviews the associated advantages, formalizes conditions under which the signal-to-noise ratio
is conserved, and describes the evolution of this architecture from first principles.
This new satellite radar altimeter concept uses on-board real-time partially coherent processing to realize an along-track impulse response shape and position which are not degraded by terrain slope or elevation. The key innovation is delay compensation, analogous to range curvature correction in a burst mode synthetic aperture radar. The detected outputs of many bursts are incoherently integrated to accumulate more than one hundred equivalent looks. The along-track footprint size is on the order of 200 - 300 meters. The radar equation for the delay/Doppler radar altimeter has an h(-5/2) dependence on height, which is more efficient than the corresponding h(-3) factor for a pulse-limited altimeter. The radiometric response obtained by the new approach would be 10 dB stronger than that of the TOPEX/POSEIDON altimeter, for example, if the same hardware were used in the delay/Doppler mode. The concept is a candidate small satellite instrument for earth observation, with particular suitability for precision altimetry of coastal and polar ice sheets.
Tropical radar environmental information system (TREIS) is a concept for a system of tropical forest monitoring based on satellite radar remote sensing. The approach is novel--starting from the ground up. TREIS offers a way around three major obstacles that are likely to preclude large-scale use of currently planned space radars: (1) high primary data cost; (2) complex and centralized ground segment infrastructure; and (3) a less than optimum radar wavelength. The proposed system is specified based on existing regional capabilities in data reception, processing, and utilization. The space segment uses existing AVHRR class data telemetry (625 Kbps), and partial on-board preprocessing of the P-band (75 cm) synthetic aperture data. Aggregate coverage of the earth''s tropical forests twice a year is achieved with ten look imagery of 20 km usable swath width and pixel spacing of 50 m. Image processing requires only work stations or high-end PC-class hardware which could be distributed over many regional centers. Data products could be prepared rapidly and inexpensively for regional use and for global inventory efforts such as those of the United Nations.
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