A versatile sonar system for ocean research and fisheries applications

An echo sounder has been developed with features ideally suited to oceanographic and fisheries research. Instruments commonly used for such research are inaccurate, limited in dynamic range, unstable, and generally inflexible. An effort has been made to overcome these deficiencies with the sonar system discussed here. The echo sounder to be described has a time-varied-gain receiver (
20 log_{10} R
or
40 log_{10} R + 2\alphaR
) accurate to within
\pm0.5
dB over a 100-dB range. The equivalent dynamic range is 140 dB (the ratio of the maximum signal at minimum gain to the equivalent input noise at maximum gain in a 4-kHz bandwidth). The temperature stability is
\pm0.5
dB from
10\deg
to
35\deg
C at any range. Operating parameters, including frequency, can be easily altered to accommodate a variety of needs.