Transitions in the polarimetric radar scattering properties of the sea surface

The wide variability of sea surface conditions is reflected in a corresponding variability in sea clutter characteristics; moreover, these characteristics manifest a strong dependence on radar parameters such as frequency, waveform and polarisation. Ideally, radar systems should adapt their parameters to the prevailing sea conditions and viewing geometry so as to optimise performance. In practice this is seldom done, in large part because most radar systems have very limited capability to adapt, but also because the rules that might guide the adaptation process are not yet clearly established. Where an appreciable change in radar parameters or viewing geometry would yield only a slight change in clutter severity and a commensurately modest improvement in radar performance, there is little incentive to adapt. On the other hand, if there are sharp transitions in clutter properties as some radar parameter is varied, then exploitation of the transition may be highly advantageous. This study presents the results of a search for transitions in polarimetric X-band sea clutter, focusing on the dependence on scattering geometry. Experiments were conducted to study clutter variation with elevation angle and azimuth with respect to wind direction. The results demonstrate that transitions exist, that they can be surprisingly sharp, and that the consequences for target detectability may be significant.