Ocean imaging with two-antenna radars

Synthetic-aperture radar (SAR) measurements are affected both by the radar backscattering cross section ( sigma /sup 0/) and by the radial velocity (V/sub r/) of the surface. An analysis of the capabilities of two-antenna SARs using a method for forming radial-velocity images to provide a general framework for evaluating the performance of different possible measurements is presented. Several key results are derived. One can measure sigma /sup 0/ and V/sub r/ separately, given a properly designed SAR. The error in V/sub r/ depends on the thermal noise in the receivers, the spacing of the two antennas, the coherence time of the surface ( tau /sub c/) and the spatial resolution of the measurement. There is an optimal separation of the antennas proportional to v tau /sub c/, where v is the speed of the aircraft. In cases where radial velocities are unimportant, two-antenna SARs can be used to image azimuth-traveling waves with wavenumbers larger than the usual azimuth cutoff. The authors show how phase errors affect the accuracy of the measurement of V/sub r/. In this development, they also provide a simple explanation for velocity bunching, a subject that has caused much controversy.<
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