Chemistry Reference
In-Depth Information
Slick radar image modelling with an extended “VIERS-1”
wave spectrum
Harm Greidanus
TNO Physics and Electronics Laboratory, Den Haag, The Netherlands
present address: European Commission Joint Research Centre, Ispra, Italy
Abstract.
The VIERS-1 model (Janssen et al. 1998) was originally de-
vised 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 re-
laxation toward that equilibrium, with and without slicks present. It was at-
tempted 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 in-
crease 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 pub-
lished measurements.
1 Introduction
Radar is a valuable sensor for the maritime environment. It can provide in-
formation about a great variety of features and processes, such as wind,
waves, currents, ships, bathymetry and natural and man-made slicks. When
oil spills are at issue, the pertinent questions are location, extent, thickness,
type and age, and the prediction of these. Some of these questions may be
answered on the basis of imaging radar data. At the same time, also natural
slicks alter the radar properties of the sea surface, thereby complicating the
interpretation of radar imagery when the interest is aimed at other features.
Therefore, it is necessary to understand the characteristics of slicks, both
man-made and natural, in radar images.
