Showing papers by "Vladimir Kudryavtsev published in 2006"

Radar scattering of the ocean surface and sea-roughness properties : A combined analysis from dual-polarizations airborne radar observations and models in C band

Abstract: [1] An analysis of radar observations in C band combined with models is proposed to study some of the ocean surface properties and their relation with the sea surface backscatter. The electromagnetic part of the models is of different kinds: composite Bragg model with or without including effect of wave breaking zones on the normalized radar cross-section (NRCS), geometrical optics approximation and small-slope approximation model. The surface description is based on the wave spectrum proposed by Kudryavtsev et al. (2003), but tests with the spectrum of Elfouhaily et al. (1997) are also discussed to assess our conclusions. The originality is to use not only the NRCS in HH and VV polarizations, but also their difference in linear units. First, we show that the upwind-to-downwind anisotropy of the radar signal cannot be explained entirely by the modulation of Bragg waves by longer surface waves, but that an additional nonpolarized contribution must be invoked to explain it, consistently with scattering from zones of enhanced roughness associated with breaking waves. Then, combining a composite model and observations in the two polarizations, we assess the contribution of the nonpolarized backscatter on the total NRCS. Finally, the proposed full model, which takes into account the nonpolarized contribution over breaking zones, gives good agreement with the observed polarization ratio and with the NRCS in each polarization.

Marine Monitoring of the South- and East China Seas Based on Envisat ASAR

Abstract: Monitoring of the Southand East China Seas has been carried out for the period January to September 2005 with Envisat ASAR as the primary source of data. More than 130 Wide Swath scenes have been collected, showing a wide spectrum of oceanic features, such as current fronts, internal waves and wind generated surface waves, as well as rain cells, oil slicks, natural films and ships. Two software tools are here used to analyse the ASAR scenes: SARTool is a software developed for the analysis of SAR data for marine applications, and can be used to get quantitative estimates of wind and waves and to detect oil slicks and ships. The other tool used is the Radar Imaging Model (RIM), which couples a hydrodynamical model and a radar transfer model to calculate the radar backscatter that a SAR would measure for given wind speed and direction, surface current, surface film and, boundary layer stability, and radar geometry and wavelength. This paper shows some examples of applications of these two models to a selection of interesting ASAR scenes.