Estimation of Directional Wave Spectra from HF Radar Sea Echo Doppler Spectra

The use of oceanic radar to measure currents at the sea's surface has become practicable. Many observations of currents in coastal zones have, in fact, provided quite worthwhile results. In contrast to this, the measurement of ocean waves by oceanic radar is still at the theoretical level. Bayesian estimation may be applied to obtain directional wave spectra from Doppler spectra. This method is, in theory, applicable, but noise contaminates the measured Doppler spectra so that they deviate significantly from the ideal. Bayesian estimation relies solely on second-order backscattering components, yet accurate estimation of directional wave spectra from observed Doppler spectra requires the proper separation of the first- and second-order backscattering components of the Doppler spectra; this is a difficult task because of the great variety of observed Doppler spectra. A method where we apply wavelet multiple-resolution analysis to separate out the first- and second-order backscattering components of the spectra is discussed. In addition, a new method where we apply both the first- and second-order backscattering components to obtain directional wave spectra that have better resolution is described. Finally, HF oceanic-radar facilities along the Kashima coast were used to conduct a series of field measurements of Doppler spectra, from which the directional wave spectra were then estimated. Simultaneous observations were made with a wave-gage array, and subsequent comparison showed good agreement with the results obtained from the HF oceanic radar observations.