Effects of transducer motion on echo-integration techniques

Abstract

Deviations in a time-integrated sonar-echo signal caused by angular motion of the sonar transducer have been calculated. The effects are due to the change in orientation of the transducer between the times of transmission of the acoustic pulse and reception of the resultant echoes. The transmission and reception beams are then aimed in different directions than in the static case. If the beams are narrow enough in relation to the augular displacement, then the departures of the integrated echo from the static case will be significant. The deviations are presented for several beamwidths as a function of angular displacement of the transducer. The results quantify the expected outcome—the change in echo-integration values from the corresponding static case increases with both increasing angular displacement and decreasing beamwidth. In an example calculation, a ship-mounted transducer is shown to roll in conjunction with the ship an angle of 4° between the times of transmission and subsequent reception of echoes from a collection of randomly distributed 400-m-deep targets. It is demonstrated that for a circular transducer, the deviations in this case can range from 1.4% to 64% for beamwidths of 40° down to 5°, respectively.