Particularities of radar backscattering associated with wave breaking on the sea surface

Abstract

Dual-polarized microwave radars are of particular interest nowadays as perspective tool of ocean remote sensing. According to conventional models the microwave radar backscattering at moderate and large incidence angles is determined by resonance (Bragg) surface waves of cm-scale wavelength range, and by non polarized (non Bragg) component which is associated with wave breaking and is supposed to be independent on polarization. At present our understanding of physical origin of different components of radar return is still insufficient. In particular, an important problem of variations of Bragg and non Bragg components (BC and NBC, respectively) along the profile of a long surface wave remains poorly investigated. This paper is focused on data processing and analysis of results of field studies of BC and NBC variations over the long wave profile using dual co-polarized X-band radar. It is demonstrated that the intensities of Bragg and non Bragg components are non-uniformly distributed over the long wave profile: BC is not strongly modulated due to long surface waves and dominates near the long wave troughs. NBC is characterized by the appearance of strong spikes near the crests of intensive long waves and contributes significantly to the radar return in the spikes supposedly due to intensification of breaking of short, cm-dm-scale wind waves. It is shown that relation between BC and NBC changes in the presence of surfactants on the water surface because of different suppression of the two components in slicks.