TABLE OF CONTENTS When the grazing angle is reduced below about 60 , sea clutter begins to show a dependence on polarisation. The assumptions behind the perfect conductor Kirchoff model no longer apply. In particular, the imperfect conductivity of sea water has a significant effect and the tangent plane approximation for the fields on the surface is very inaccurate. Without these simplifications, it is difficult to apply the general solution (i.e. equations (3.32) and 3.33) to realistic sea surfaces. Progress can be made, however, for the case where the roughness is very small. It was shown in equation (3.51) that the small perturbation limit for the perfect conductor Kirchoff model depends only upon the resonant wave number value of the surface wave spectrum. Thus
where k H is the horizontal component of the back scattered wave-vector k, and 2 k H is the resonant wave number. A similar result may be obtained for an imperfect conductor without the Kirch off approximation,
The factors g HH and g VV are given by
and ? i is the incidence angle (i.e. 90 minus the grazing angle). This SPM (small perturbation method) result, which is exact in the limits of small height and slope, was originally obtained by Rice [21] and Peake [22], using a wave expansion technique. Wright [23] obtained the same formulae using a reciprocal field method(the Lorentz Reciprocity Principle, LRP). Holliday [24] showed that...
