Ocean imaging with two-antenna radars

Synthetic-aperture radar (SAR) measurements are affected both by the radar backscattering cross section (σ⁰) and by the radial velocity (V_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 σ⁰ and V _r separately, given a properly designed SAR. The error in V_r depends on the thermal noise in the receivers, the spacing of the two antennas, the coherence time of the surface (τ_c) and the spatial resolution of the measurement. There is an optimal separation of the antennas proportional to vτ _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_r. In this development, they also provide a simple explanation for velocity bunching, a subject that has caused much controversy