Sonar modelling in fish abundance measurement

For some years estimates of fish abundance have been made using the output of an echo-sounder system. By considering the integrated energy of the echo of a shoal and with knowledge of the sonar parameters and the target strength of the species of fish involved, a crude estimate of the biomass can be made. Griffiths (1976) published some work in which a computer model of a typical sonar system was used to try to evaluate the accuracy with which the number of targets could be estimated from the integrated energy. However, the model used was fairly simple and did not take into account some important effects such as the directivity of the target strength of the fish which may have a significant effects on the estimates. The present work is an attempt to modify the computer model by considering these factors and to try to approach more nearly the practical situation