Design of a sonar for fish counting

Abstract

The paper described (a) A very high resolution echo-sounder, (b) A\nmethod of sorting echoes by amplitude and range, (c) A study of the\nanalysis required to transform from distribution of echoes to distribution\nof targets.\nUnder (a) the main parameters were - frequency 400 kHz - range\nresolution 15 centimetres - beam angle to half-power point 0.011 radians.\nThe equipment for recording echoes (b) is a pulse height analyser.\nEcho information is stored in twenty range intervals, each subdivided\ninto 20 categories of amplitude.\nIt was shown (c) that the process of determining target distribution\nfrom echo distribution can be dealt with by computer, and resolves itself\ninto a correction for angular spread of the beam, followed by a transformation\nto allow for the directivity pattern. This latter transformation\nis equivalent to solving twenty simultaneous linear equations for each\nrange element. The coefficients of the equations are constants for the\nequipment, thus the set can be solved once, and the result applied to each\nsuccessive range element by a simple programme.