SYNTHETIC APERTURE RADAR IMAGERY OF RANGE TRAVELING OCEAN WAVES

In synthetic-aperture radar (SAR) imagery of ocean waves, an image modulation by radar foreshortening exists in addition to backscatter radar cross sections. The foreshortening effect is due to surface-height differences making sections of a rough surface fall into different range bins than they would if the surface were flat. Since the degree of this modulation changes according to the local wave height, foreshortening alone could produce the image pattern corresponding to the wave field. The effect, termed range bunching, is maximum for range traveling ocean waves and vanishes for azimuth traveling waves. It also increases with decreasing radar look angle. The imaging processes of range traveling waves are investigated by taking account of both the cross section and range bunching. The SAR transfer function and image modulation functions are defined to describe the relative importance and the coupling effects of the two contributions. It is shown that in low to moderate sea states, where the major variation in backscatter arises from local surface tilt, the image modulation by the cross section is enhanced by range bunching and the effect increases with increasing wave slope and also with decreasing look angle.