Estimates of Low Frequency Volume Scattering Off the Oregon-Washington Coast
1992
Nero, R. W.
Estimates are made of low frequency volume scattering using average numbers of animals for the shell break and offshore waters off the Oregon- Washington coast. Animal densities were derived from fisheries assessments and surveys of marine mammals. Target strengths were based on resonant models of fish with swimbladders and in situ measurements of mammals. Average volume reverberation levels of -60 dB at 1 00 Hz, and -44 dB at 1 00 Hz are expected at both offshore and shelf break locations during summer nights (July-September). These levels will decline by about 7 dB by day. During winter (January- March) scattering will be low at offshore sites, less than -90 dB at 1 00 Hz and -60 dB at 1000 Hz but will remain high at the shelf break, near -61 dB at 1 00 Hz to - 48 dB near 1 000 Hz. Spring and fall are transitional between winter and summer, and hence, will have volume reverberation levels between those of summer and winter. A model of school encounter suggests that when schools of pomfret jack mackerel, anchovy, and rockfish are present they will be sufficiently widespread to appear as average reverberation levels. Schools of. albacore, coho, and chinook salmon will be sufficiently rare and compact so as to cause discrete echoes. Antisubmarine Warfare, Volume Scattering
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