Phantom motion of the ocean

Abstract

The interactions between geometrical Doppler, beam pattern, and normalized radar cross section (NRCS) result in the unwanted coupling—leakage—of geometrical Doppler into the perceived geophysical Doppler. Starting from high-resolution synthetic aperture radar (SAR) data we model this leakage for synthesized real aperture radar (RAR) observations of ocean motion. The uncertainty introduced by leakage is ∼1ms−1. Corrections proposed in this work exploit the known interactions between beam pattern and geometric Doppler with NRCS gradients retrieved from simulated low-resolution RAR to estimate and correct for the incurred leakage, reducing the uncertainty to O(0.1ms−1). Further reduction of instantaneous leakage may be achieved through temporal averaging, since the NRCS gradients that cause leakage appear mostly atmosphere induced and decorrelate rapidly. The azimuth resolution and number of independent samples determine a system’s sensitivity to leakage. C-band systems are inherently prone to suffer from greater leakage and worse corrections than their Ku- and Ka-band counterparts. With DopSCA, the propagated effect of leakage is only secondary compared to the pulse-pair uncertainty. In similar systems where pulse-pair uncertainty is suppressed, leakage will dominate instead.