TABLE OF CONTENTS Equation (3.50) for Kirchoff scattering from a perfect conductor is quite effective for modelling sea clutter at high grazing angles. The use of either equation (3.1) or 3.9 with appropriate angular dependence produces results that are consistent with experiment for angles from close to normal (90 ) out to about 60 grazing angle. Perhaps the most interesting application of this scattering model, however, is to predict the change of RCS due to local changes in the wave spectrum, S ?, which are in turn caused by ocean currents. This is the mechanism by which it appears that a space based imaging radar, such as ERS1, is able to see though the ocean to the sea-bed. What is actually happening is that the tidal currents vary as they flow over submarine topology; these change the surface wave spectrum, and this is observed by the radar. Understanding this process requires some knowledge of hydrodynamics, which is not the main subject of this book. Therefore only a brief description is given here. The reader is referred to the references for more detail.
In order to model the effect of ocean currents on the surface waves we use the theory of action balance . According to Hughes [16], application of the principles of conservation of waves and conservation of energy leads to equations in Reference [17] that may be used to derive the principle of conservation of wave action. This principle is that,...
