Slick radar image modelling with an extended “VIERS-1” wave spectrum

The VIERS-1 model (Janssen et al. 1998) was originally devised to describe ERS scatterometer measurements over the sea on a physical basis. This model is extended to include the saturation range, and it is used to derive equilibrium wave spectra and formulations for the relaxation toward that equilibrium, with and without slicks present. It was attempted to derive actual relaxation rates from the model, but this was only successful on part of the spectral range. The extended VIERS model is combined with a radar imaging model originally designed for radar bathymetry, to yield quantitative computations of radar contrast along transects through slicks. The resulting model shows an apparent size increase of the slick and a smoothing of its edges, due to the finite relaxation time of the slick-dampened, backscattering surface roughness. The present work offers no validation by observed images, but the trend in frequency and polarisation dependence of the radar contrast is supported by published measurements.