Mv. Trevorrow et Ij. Booth, EXTRACTION OF OCEAN WAVE DIRECTIONAL SPECTRA USING STEERABLE DOPPLER SIDE-SCAN SONARS, Journal of atmospheric and oceanic technology, 12(5), 1995, pp. 1087-1100
A new technique is presented for extraction of ocean wave directional
spectra using steerable Doppler side-scan sonars. The method is design
ed for use from a subsurface platform at the 25-m depth. Two 360 degre
es steerable side-scan beams at 103 kHz are used to estimate along-bea
m horizontal water motion due to waves at ranges out to 250 m. Upward-
looking sonars are used to estimate the surface height power spectrum.
This new method, dubbed ''coherent wavenumber summation,'' uses waven
umber decomposition of radial velocity versus range profiles. A wavenu
mber-directional grid is then coherently incremented over one 360 degr
ees, 64-ping sweep of the side-scan beams, which requires deconvolutio
n in time and spatial orientation. The resulting directional spreading
functions are then incoherently averaged over 30-50 min of side-scan
data. Numerical testing shows that this method can reconstruct accurat
ely realistic uni- and bidirectional seas over the frequency range 0.0
9-0.30 Hz and is insensitive to random noise. The method is demonstrat
ed through comparison with conventional array methods using data colle
cted in the northeast Pacific. The resolution of this method is severe
ly limited by the combined effects of short temporal and spatial coher
ence scales of natural ocean waves, and geometric consequences of the
finite side-scan beam aperture (<200 m).