Multifrequency SAR observationof a ship wake

The authors have developed a computer simulation to model SAR (synthetic aperture radar) images of ship wakes for various configurations. The model accounts for the surface perturbation produced by a moving ship and the influence of the sea background. Electromagnetic scattering from the surface is calculated by using a tilted Bragg theoretical model in which it is assumed that the small Bragg waves are modulated by the larger scale ambient sea waves and Kelvin wake fluctuations. The simulation combines the results of hydrodynamic and radar scatter calculations to provide SAR images of the backscattering of the ship's wake. It is shown that, in general, a high resolution SAR should perform better than a low resolution system. The decreasing resolution is one of the reasons why so few Kelvin wake observations are made in the Seasat data (1992). So the authors' simulation uses an airborne configuration with a spatial resolution achieving a resolution cell of a few square metres. Two frequency polarised responses (L- and X-band) to the Kelvin wake embedded in the sea clutter are presented. These images show that the features are clearly resolved for at least one frequency for different polarised channels. Some of these signatures may contribute to the detection of the ship and help to extract information about it.