Processing of ocean wave data from a synthetic aperture radar

The usual operation of a synthetic-aperture radar (SAR) assumes that the sensor platform moves at a constant velocity along a straight line and that objects to be imaged are stationary. Moving ocean waves perturb the Doppler frequencies in the SAR phase histories, and when processed in a conventional manner, they produce images of waves that are dispersed and thus defocused in the azimuth (along-track) direction. This defocusing can be compensated in the processor by readjusting the azimuth focus by an amount proportional to the velocity of the wave.The relationship among the parameters of the radar system, the SAR processor, and the relative target velocity is, theoretically determined for radars that operate at both X- and L-band frequencies. Experimental observations support these calculations. The effect of varying spectrum sampling, range focus, and number of coherent averages or looks is also observed.