Limitations of the Two-Scale Theory for Microwave Backscatter from The Ocean

Abstract

Radar imagery of the sea surface reveals both surface features (e.g. wind structure, swell waves) and sub-surface features (e.g. internal waves, tidal flows over submerged sand banks). In addition appear a variety of man made objects (e.g. rigs, vessels) which may be sensed directly or via their effects on the oceanic environment (i.e. their wakes). An important part in the proper interpretation of such images is a thorough understanding of the scattering of microwaves from the sea surface. The other essential part of the problem is the hydrodynamics of the short wind waves and their modulation by the currents induced by surface and internal features. In the absence of wind the ocean is glassy-smooth giving trivial specular mirror scattering, largely irrespective of the presence of oceanic features. It is thus important to understand first the scatter from a wind-generated rough ocean surface (wind scatterometry) and later, the scatter in the additional presence of ocean features.