A coherent averaging technique for resolving directional wave spectra

A new technique has been developed for deriving the directional spreading function of ocean waves from an array of water velocity measurements. The objective was to efficiently process data from a 118 kHz Doppler sidescan sonar which measures water velocity parallel to the sonar beam at a series of ranges. The sonar beam rotates as it collects data, rendering techniques such as the maximum likelihood method unusable. A numerical process was developed wherein the data are transformed into wavenumber space, deconvoluted in space and time, and coherently averaged over successive sweeps of the sonar. The method was tested on velocity arrays simulated from computer models of the sea surface, and used on experimental data. It proved to be computationally efficient and very insensitive to noise.<>