Patent GB-1270245-A (GB)
Title: Fish counting apparatus
Inventor: BERKTAY HASAN ORMAN
IPC: G01S15/96
Filed: 1968-06-11
Abstract: 1,270,245. Acoustic detection devices. NATIONAL RESEARCH DEVELOPMENT CORP. 10 June, 1969 [11 June, 1968], No. 27606/68. Heading H4D. [Also in Division G4] Apparatus for counting fish passing through a water channel comprises means for beaming acoustic energy across the channel to illuminate the channel in two cross-sectional planes spaced from each other longitudinally of the channel, and a counter actuated only if echoes are detected from both planes. The beaming arrangement for each plane may be a respective column of transducers producing pencil beams which together cover the whole depth of water. As fish may be expected to cross both planes at the same height, separate pulse-echo detection circuits for the pencil beams can give depth information to discriminate against false echoes. Alternatively the beaming arrangement for ecah plane is as in Fig. 1b, comprising transducers 10, 11 respectively giving downwardly and upwardly inclined fan beams together covering the plane. Transducer 10 is mounted, e.g. on a float, to move if the water depth changes, so that reflection from the water surface is avoided. Echo pulses received from one plane by transducers 10, 11 are fed through amplifiers 14, 15, which compensate for increased attenuation with range, to discriminators 16, 17 each of which is such that it provides a standard height output pulse if its echo input exceeds a threshold amplitude and is of width about equal to the transmitted acoustic pulse width (thus discriminating against echoes from weeds). In order to count several fish swimming adjacently the channel can be divided into several preset range intervals in each of which the echoes are processed separately. For wide water channels a more economical arrangement is as in Fig. 2 in which range interval selection unit 18 (with as many signal channels as there are fish likely to be swimming adjacently), gates the first-arriving discriminator output pulse to a first channel, the secondarriving pulse to a second channel and so on. Delay circuits 19, each with a delay equal to one transmitted pulse repetition period, open their respective channels only at the instant an echo at the respective range is expected. Thus in subsequent repetition periods, echoes at a given range will be gated to the same channel. If a minimum number, e.g. three, of such echoes are received in a given channel, as determined by a unit 21 comprising a shift register and comparator, the comparator gives an output signal. The Fig. 2 apparatus is duplicated for the other plane, and if both comparators for a given range channel give output signals then a fish count is indicated. To prevent double counting if the fish is in the region of overlap of the two fan beams from transducers 10, 11, transducer 11 output is fed through range inverter 20 which gives an output pulse at a time corresponding to that range which is the complement, relative to the total width of the water channel, for each input pulse. The direction of fish travel is determined by noting which of the two comparators indicates first.