This work reviews high-frequency, low-grazing angle surface and bottom
reverberation effects relevant to fish detection in shallow waters. S
imple acoustic reverberation models are presented, which include the e
ffects of Bragg scattering from surface wind waves, sediment backscatt
er, and scattering and absorption within air bubble layers created by
breaking waves and boat wakes. A simple example, with a 200 kHz narrow
-beam sonar in water depth of 5 m, is used to demonstrate these reverb
erative interference effects. When present, air bubble layers cause se
rious interference with fish detection, such that even large fish (TS
= -30 dB) could not be detected beyond 50 m range. Under calm conditio
ns without bubbles, reverberation from gravel or rocky sediments would
limit detection of small fish (TS = -50 dB) at ranges greater than 50
m. Air bubbles within boat wakes generate strong backscattering and c
ause shadowing (transmission loss exceeding 20 dB) of targets behind t
hem. (C) 1998 Elsevier Science B.V.