GB1330472A - Sonar systems - Google Patents

Abstract

1330472 Echo-sounding EMI Ltd 21 Dec 1970 [19 Dec 1969] 61906/69 Heading H4D A method of correcting sonar charts includes detecting by sonar the variations in relative position of at least one reference object as the echo receiver is moved and utilizing the difference between the expected detected variations to correct further sonar indications for errors due to velocity gradients in the transmitting medium. A sonar source (1, Fig. 1, not shown carried on a ship transmits a fan-beam to the sea-bed aligned along the ships track. The echoes are recorded on a strip chart 10, Fig. 2 (b) and the strip speed is such that if no vertical velocity gradient is present the locus of the point 3 Fig. 2(a) is recorded as a line 3T at 45 degrees to AA<SP>1</SP> which represents the ship's track. The actual detected locus is however 3 0 . The plan range error is zero at 3 3 when point 3 is vertically below the ship. Thus a line drawn at 45 degrees to AA<SP>1</SP> through 3 3 enables the variation of the error with plan range to be determined for all points along AA<SP>1</SP>. When the normal side-looking sonar charting is effected the error function is used to modulate the display writing scan. Errors due to currents in the sea, may be similarly dealt with except that the error is a maximum near the ships track and the detected locus is asymptotic to the true locus at the extremities of the chart. When both errors are present the true locus is drawn such that the errors at both chart extremities is equal but opposite in sense. The sea-bed depth is also recorded 13, and utilized in the error function. The fan-beam may be replaced by a number of pencil-beams or a single pencil-beam used to track a single echo source as the ship moves.