Patent GB-1238965-A (GB)
IPC: G01S15/42
Filed: 1969-03-19
Abstract: 1,238,965. Sonar systems. FRIED. KRUPP G.m.b.H. 19 March, 1969 [20 March, 1968; 31 July, 1968], No. 14475/69. Heading H4D. In an echo-sounding system wherein the angular position of a target, relative to a reference direction perpendicular to the plane of a transducer array, is displayed on a singlebeam cathode-ray tube (C.R.T.) having deflection voltages respectively representing the target azimuth and elevation relative to said reference direction, the centre of the transducer array is indicated as a centre display point on the C.R.T. screen, or on a portion of the screen allotted to the display of the angular position of the target. In the Fig. 1 embodiment, 5 is an array of transducer elements arranged in verticallyspaced groups 1, 2 and horizontally-spaced groups 3, 4. The array is mounted in a streamlined housing (not shown) which is attached to a trawl net and can swivel so that the boresight axis is aligned with the direction of motion of the net relative to the water. A voltage U #  vert proportional to the sine of the elevation angle of a reflecting object (fish shoal) is provided by one phase comparator 6 from the echo signal outputs of transducer groups 1, 2; a voltage U #  hor is similarly derived for the object azimuth angle from the echo outputs of groups 3, 4. These voltages are multiplied at 8 by a factor representing object range (derived by sawtooth generator 9) and the respective product voltages U vert and U hor provide the Y and X deflection voltages for C.R.T. 11. The echo signals are summed at 7 and fed via gate 13 to intensity-modulate the C.R.T. display. Gate 13 is opened only if comparator 10 determines that U vert and U hor are simultaneously constant, this condition being characteristic of fish shoals and not of water bottom or surface echoes. Display of echoes from objects in a selected partial range is obtained by means of trigger circuit 12 which delays the opening of gate 13 from the instant of transmission of an acoustic pulse. A digital indication of range (in a selected partial range) may be given on a counter. If the C.R.T. is a double-beam type, one beam is used for the perspective azimuth/ elevation display and the other beam provides a conventional display of object range. The acoustic beam width may be varied (by changing the acoustic frequency or the number of transducer elements in a group) according to the partial range selected, to give a narrower beam and hence improved signal-to-noise ratio at long range. In the Fig. 7 embodiment, the transducer elements are arranged in two vertically spaced groups and a set of discrete reception beam lobes angularly spaced in azimuth is obtained by means of a network 15. For each reception direction the echo signal outputs of a vertical pair of elements are phase compared at 6 to give a respective voltage representing object elevation angle and this voltage is multiplied at 8 by the range factor (as in Fig. 1) to give a U vert voltage. The U vert voltages are sequentially scanned by electronic switch 46 and provide Y deflection of the C.R.T. beam, while the beam is stepped in the X direction by a deflection voltage obtained from divider chain 19 via electronic switch 18 and while a summation voltage from adders 7 is applied via electronic switch 17 to intensitymodulate the beam.