Mv. Trevorrow, DETECTION OF MIGRATING SALMON IN THE FRASER-RIVER USING 100-KHZ SIDESCAN SONARS, Canadian journal of fisheries and aquatic sciences, 54(7), 1997, pp. 1619-1629
During a 10-day period in September 1995, field trials were conducted
in the Fraser River near Mission, B.C., to evaluate 100-kHz side-looki
ng sonars for salmon detection. A two-element sidescan installation lo
oking transverse to the river flow detected echo traces due to salmon
at ranges up to 250 m in water 6-13 m deep. The salmon target trajecto
ries were identified and counted against a background of acoustic reve
rberation from the river surface and bottom sediments. Occasional, str
ong interference from boat wakes and wind-induced surface waves and bu
bbles was observed. Fish echo trajectory analyses allowed extraction o
f upstream and cross-stream swimming speeds. For some targets acoustic
multipaths from surface and bottom reflections were distinguishable f
rom direct echoes at ranges up to 150 m. Acoustic models of surface an
d bottom boundary backscattering, combined with bubble layer scatterin
g and attenuation under breaking wave conditions, were able to match t
he observed background echo levels. Comparisons of model and data pred
ict that under ideal conditions fish detection should be possible at r
anges up to 250 m, but under windy conditions detection was limited to
less than 70 m.