Aspect dependence of the polarimetric characteristics of sea clutter: II. Variation with azimuth angle

The dependence of the spatial, temporal, Doppler and polarization characteristics of monostatic microwave radar sea clutter on the direction of observation relative to the prevailing sea direction has been the subject of many investigations. In most instances, though, the data and interpretation have focussed on the upwind/downwind and cross-wind directions, rather than exploring the detailed azimuthal variation. Such a policy certainly establishes the key qualitative differences in radar signature which reflect the influence of scattering geometry on scattering characteristics, but is not adequate to guide the optimization of viewing geometry for specific missions. For example, it may be that the scattering properties are simplest over some range of intermediate angles, with benefits to echo interpretation as well as providing a means to validation of modeling techniques. To address this issue, we conducted an experiment at Ardrossan, in Gulf St Vincent, near Adelaide South Australia, where X-band sea clutter was measured over 270deg of azimuth with 4deg beams at ~ 22.5deg spacing. This paper presents the initial results of an investigation of the azimuthal variation of the polarimetric structure of the dominant clutter returns. A companion paper explores the variation with the angle of incidence in the vertical plane.