Design of a sonar for fish counting
Abstract
The paper described (a) A very high resolution echo-sounder, (b) A
method of sorting echoes by amplitude and range, (c) A study of the
analysis required to transform from distribution of echoes to distribution
of targets.
Under (a) the main parameters were - frequency 400 kHz - range
resolution 15 centimetres - beam angle to half-power point 0.011 radians.
The equipment for recording echoes (b) is a pulse height analyser.
Echo information is stored in twenty range intervals, each subdivided
into 20 categories of amplitude.
It was shown (c) that the process of determining target distribution
from echo distribution can be dealt with by computer, and resolves itself
into a correction for angular spread of the beam, followed by a transformation
to allow for the directivity pattern. This latter transformation
is equivalent to solving twenty simultaneous linear equations for each
range element. The coefficients of the equations are constants for the
equipment, thus the set can be solved once, and the result applied to each
successive range element by a simple programme.
Publisher
[Fiskeridirektoratets havforskningsinstitutt]Series
Fiskeridirektoratets skrifter, Serie Havundersøkelservol 15 no 3