On a two-scatterer theory of sea echo

Results of visual observations and statistical analyses on the polarization dependence of fluctuations in radar echo are given. Some data are also given on relative power, as a function of polarization, contained in the two distinctly different fluctuation spectra observed. The fast fluctuations are from wind ripples, and the slower fluctuations are strongly dependent on the sea structure. The information on fluctuations is given as support of a two-scatterer concept for sea echo. The scatterers are: 1) a wind-dependent fine structure of the sea (ripples) interspersed with 2) smooth areas (facets) of the wave structure. The composite theory for rough surfaces developed recently in both the United States and the Soviet Union predicts that average radar cross section of sea echo for transmitting and receiving horizontal polarization never exceeds that for vertical polarization. However, measurements at near grazing incidence yield average HH cross sections that sometimes exceed average VV cross sections, and the observations reported herein suggest that reflection from facets is the cause. The composite theory includes the facets only in the sense of varying the slope of the waves on which the ripples are located. Therefore, the need is emphasized for a sea echo theory that is applicable to small incidence angles and includes the effects of the facets.