Influence of Currents and Waves on the Doppler Spectra of Ocean Radar

The method of velocity measurement using an Ocean Radar has already come into practical use.However the measured velocity is sometimes not reliable because the first order Doppler spectra may have double peaks or flat peaks.To reveal the influent factor on the shape of the spectrum, effects of currents and waves are analyzed using observed data and model calculation results of Doppler spectra.Results show that current unsteadiness make the spectrum peaks flattened, and that horizontal shear and convergence of current cause double-peaked spectra.The second order Doppler spectra depend on the period and direction of the sea surface wave.We propose a simple equation estimating the significant waveheight from the measured Doppler spectrum.