Doppler Techniques Applied to Fisheries Hydroacoustics

Fisheries management agencies are in need of better technologies to monitor the runs of migratory species in free-flowing rivers. This paper describes a long-pulse 420 kHz riverine Doppler sonar designed to detect upstream migrating fish in shallow waters and to reject false targets and large reverberations from the surface and bottom. The use of Hanning-shaped long pulses (30 msec) results in good spectral separation between reverberations and Doppler-shifted echoes from upstream migrants. A correlation detector rejects certain classes of false targets by comparing shapes of the transmit pulse and Doppler-shifted echoes. The correlation detector also improves the system´s range resolution. In field tests the system has provided an accurate run timing index of the spring 1983 sockeye salmon run on the Quinault River in Washington State. Current research includes investigating bistatic configurations for monitoring fish passage through specific regions and the use of echo integration techniques to sum the total energy in the received signal.