A broadband echo ranging system for measuring the frequency characteristics of fish schools

A broadband echo-ranging system has been employed to collect echoes from fish schools off the southern California coast. The system uses an implosive impulse source called Hydroshock^(R)and a broad-band, constant beamwidth towed array. The equipment is capable of measuring target strength from 500 Hz to 50 kHz, with minimal frequency distortion due to transducer beamwidth effects. Averaged frequency spectra for echoes from several schools are presented, showing different cutoff and resonance characteristics.