DIRECTIONAL SURFACE-WAVE ESTIMATES FROM DOPPLER SONAR DATA

A ''quick'' refers to both the short time span of data required and computational ease. The technique employs time and space Fourier transforms to estimate the frequency-wavenumber power content for each sonar beam. The directional information is converted into the first for circular Fourier components at each frequency (including the mean power estimate) to facilitate rotation to true north coordinates. The motivation is to estimate the lowest few circular Fourier components of the directional wave distribution robustly and efficiently, without reducing the statistical stability afforded by the spatial extent of the array. Several potential difficulties inherent to Doppler sonar data are discussed in some detail; the quick analysis is robust with respect to these concerns. Using data from the Surface Wave Process Program (SWAPP), the quick analysis results are compared to those from a three-wire array. The directional components are estimated with reasonable statistical stability from 13-min segments: for example, the mean wave direction has an rms error of about 6 degrees. Comparable accuracy from the wire array requires averaging for about four times as long.