Mv. Trevorrow, MEASUREMENT OF OCEAN WAVE DIRECTIONAL SPECTRA USING DOPPLER SIDE-SCANSONAR ARRAYS, Journal of atmospheric and oceanic technology, 12(3), 1995, pp. 603-616
A technique is presented for extraction of ocean wave directional spec
tra using Doppler side-scan sonars. Two 103-kHz steerable side-scan be
ams from a freely drifting subsurface platform are used to estimate ho
rizontal water surface velocity due to waves. The side-scan targets ar
e clouds or layers of microscopic air bubbles, confined to within a fe
w meters of the ocean surface. Upward-looking sonars are used to estim
ate the surface height power spectrum. The side-scans are steered to c
ompensate for any platform yaw, and corrections to the measured wave v
elocity due to horizontal and vertical platform motion must be applied
. Measurements of wave velocity with the side-scans in this geometry a
re found to have acceptable spectral signal-to-noise properties at hor
izontal ranges up to 150 m in the frequency range 0.05-0.35 Hz, with d
egraded performance at greater range. Time series of horizontal wave v
elocity at 16 range points along each of two orthogonal beams are used
in a maximum-likelihood array processing technique to estimate the di
rectional spreading functions versus frequency. Numerical and experime
ntal tests suggest that the maximum-likelihood method can reconstruct
adequately unimodal and bimodal wave fields. These methods are demonst
rated with ocean data from the northeastern Pacific.