Model analysis of influence of wave-current interaction on current measurement of HF ocean surface radar for isolated eddy and upwelling

[1] The influence of wave-current interaction on the current measurement of HF ocean surface radar (HFOSR) is analyzed by a simulation of the Doppler velocity spectra of the first-order echo. The Doppler velocity spectra is a product of the spatial integration of the radial velocity weighted by the radar sensitivity and the normalized radar cross section (NRCS). As a result of the wave number change due to the wave-current interaction and the extension of the wave packet due to the divergence of ocean currents, the NRCS distribution becomes nonuniform. The artificial component is produced around the center of the current phenomena in the simulated radial velocity field because the nonuniformity of the NRCS distribution distorts the spectral shape of the first-order echo. The artificial component flows in the opposite direction of the propagation of the causal ocean waves. The intensity of the artificial component depends on the spatial scale ratio of the radar sensitivity distribution to the current phenomenon. In addition, the spatial averaging effect caused by the radar sensitivity distribution leads the antisymmetric component of the radial velocity difference, which weakens the intensity of the simulated current phenomena. The averaging of the two radial velocities extracted from the two first-order echoes, corresponding to the approaching and receding causal ocean waves, is effective in reducing the artificial component in the measured radial current velocity by HFOSR, because the artificial components in the simulated radial velocities have almost the same spatial distributions with the opposite direction of flow.