Acoustic estimates of fish density and scattering function

The signal processing techniques for acoustically estimating fish abundance are echo counting and echo integration. The transducer beam pattern complicates these estimates. We (1) statistically model the effects of the beam pattern on scattered signals, (2) compare acoustic data to this model, and then (3) for echo from individual fish, calculate estimates of fish density and scattering function based on these comparisons. At low densities we determine the proportionality constant relating the average echo integral and fish densities. Then at high densities, this proportionality is used to estimate fish density. The theory is compared to experimental data for alewife in Lake Michigan, U.S.A.