Estimation of current velocity using circular SAR data

A method of current velocity estimation using airborne sea data is proposed. The sea data are collected by circular synthetic aperture radar. The range Doppler image can be acquired after range and azimuth compression for each beam scan angle. The corresponding average Doppler spectrum can be obtained and fitted to Gaussian shape well. Hence, the Doppler centre shift can be represented by the mean of Doppler spectrum. It is observed that the Doppler centre varies with the beam scan angle and the variation is approximately a sinusoid-shape function. The velocity and direction of current in a local area are fixed so the radial velocity caused by the current is a harmonic function of the scan angle. Therefore, the current velocity can be obtained by the amplitude of the harmonic. Actually, the radial velocity does not only include the current, but also includes the surface wave motion. However, the method presented can obtain the real current velocity directly, avoiding adopting the radial velocity of the scatterer, so the estimation of the current velocity is accurate.