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 1×1 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