AN EMPIRICAL-EVALUATION OF THE DURATION-IN-BEAM TECHNIQUE FOR HYDROACOUSTIC ESTIMATION

The duration-in-beam is an empirical technique for estimation of the effective sampling angle of a hydroacoustic beam. The technique potentially allows estimation of fish densities without the usual requirements for system calibration and target strength information. Duration-in-beam measurements from 50 hydroacoustic surveys of juvenile sockeye salmon (Oncorhynchus nerka) in Alaska [USA] were used to examine the variability in the technique. The results showed reasonable consistency in the beam angle measurement and indicated that the technique was not subject to the estimation errors usually associated with uncertainty in the acoustic system calibration and target strength parameters.