ABSTRACT
This chapter analyzes the peculiarities of detecting and registering commercial items in order to clearly imagine the possibilities of acoustic instruments regarding various fishing conditions. With the help of acoustic instruments it is possible to quickly detect commercial concentrations of biological items, determining the distance and bearing, the dimensions and depth of their submersion. The possibilities of detecting biological items depend not only on the range, detection zone, and resolving capacity of acoustic instruments, but also on the character of distribution of commercial items. The character of images of individual items and their concentrations on the echograms of acoustic instruments is determined by the parameters of the devices themselves. A fish-finding echo sounder registers commercial concentrations distortedly; records of schools and concentrations differ in shape from real ones. Echo signals can arrive at the transducer of an echo sounder in the normal way as well as by a more complicated one.
