Determination of the near surface current field from Doppler shift of the coherent radar backscatter under grazing incidence

The aim of this work is to develop a radar remote sensing system for the retrieval of a current map with a spatial coverage of around 1/spl times/1 square kilometers and the resolution of a conventional radar. In co-operation with the Electro-Technical University of St. Petersburg a nautical radar, which normally detects only the amplitudes of the backscatter, is upgraded by a second, 90 degree phase shifted output- channel, to get a coherent signal. With a coherent system the surface current can be detected by the Doppler frequency shift of the backscattered signal. In comparision to a full coherent radar the advantage is clearly the very low price. In this presentation Doppler spectra taken in the Finish Gulf in October'98 during the first test phase of the new system are shown and the problems due to the influence of the wind speed and surface waves are discussed.