Two-dimensional imaging mechanisms of ocean waves by synthetic aperture radars

Abstract

Expressions are derived and discussed for the local mean intensity of the two-dimensional images of ocean waves produced by a synthetic aperture radar (SAR). Accounts are taken of the spatial and temporal changes of both back-scattered radar cross-section and ocean wave height. It is shown that the images of ocean waves are distorted as a result of radar layover. This imaging process is similar to velocity bunching by the effect is largest for range waves and it vanishes for azimuth waves. The mechanism of defocusing is also investigated. If reference signals are designed for stationary objects, the images of dynamic waves are always defocused, irrespective of their propagation direction and of the types of imaging processes, including radar layover, velocity bunching and back-scattered cross-section. Defocusing originates from the systematic degradation and upgradation of point spread (impulse response) functions associated with the periodic structure of the waves. The images can be enhanced by applying a defocused azimuth reference signal and the amount of defocusing for optimum images depends only on the wave phase velocity and propagation direction.