At-sea measurements of diver target strengths at 100 Khz: measurement technique and first results

Abstract

During a recent at-sea trial of a diver detection system, the opportunity was taken of developing a technique for in-situ measurement of diver target strengths. The technique was based on making the diver perform circular manoeuvres in front of the sonar to present all aspect angles to the sonar. The diver was made to perform the circular manoeuvres by means of tethers attached to the diver, from a seabed anchor and a surface float, ensuring constant radius and depth about a fixed point. Otherwise, the diver was uninhibited in limb movement, attitude, exhalation rate.

The experimental set-up employed, the procedure employed, how the set-up complied with the far-field requisite and how the multipath effects were eliminated are discussed in Sect. 2. A transformation of coordinates (by change of origin), the inverse transformation and how the transformation was employed in aspect angle estimation are discussed in Sect. 3. An application to the case of a diver with air tanks, exhaling clouds of bubbles into the water column, and how a target tracker was developed to locate the diver are discussed in Sect. 4. The first results are presented in Sect. 5.