Measurements and modeling of the target strength of divers

Acoustic methods (sonars) offer a potential tool for detecting and tracking of underwater swimmers. The main unknown in assessing the feasibility of using sonar to detect swimmers is their target strength. The target strength of diver with tanks, buoyancy control, wet or dry suit, etc. is a complicated function of aspect angle and frequency. The detection range for a diver will depend strongly on the target strength and very little data are available in the literature on this topic. This dearth of information limits the ability of sonar engineers to design a detection system. Our study addresses this issue both experimentally and theoretically. As part of this study target strength measurements made in the field were compared with theoretical models. Measurements are being conducted using Farsounder FS-3 phased array sonar with a center frequency of 60 kHz. Tests will be carried out in shallow water using a diver at different orientations, depths and ranges. Target strength modeling was performed using simple cylindrical models and more sophisticated techniques. Existing target strength models for finite cylindrical shapes derived by Gaunaurd (1985) were used as initial approximations. A relatively new technique for modeling acoustic scattering by axisymmetric finite-length bodies using a three-dimensional Fourier mapping method developed by Reeder and Stanton (2004) was compared to the data.