ASA 124th Meeting New Orleans 1992 October

1aUW17. Beam noise and array gain models for computing ship resolution gain.

D. W. Craig

L. Tan

Defence Res. Establishment Pacific, F.M.O. Victoria, Victoria, BC V0S 1B0, Canada

Array gain estimates for horizontal towed array systems in ship-induced noise fields are typically predicated on the assumption of a constant noise power in the horizontal azimuth. Large-aperture arrays operating in such fields are able to resolve individual ship interferers and are capable of enhanced detection gain in regions of reduced noise. This enhanced gain, known as ``ship resolution gain'' (SRG) [Heitmeyer et al., NRL Report 8863, Feb. 1985] represents an additional term that must be added to the sonar equation. A revised model is presented that computes beam noise distribution functions numerically, without Heitmeyer's approximation of mainlobe/sidelobe sectors, and illustrates the effects of steering angle, hydrophone shading, sidelobe degradation, and shipping density. This model assumes a Poisson shipping density and computes beam noise as the finite sum of contributions from individual ships. The SRG in the revised beam model is compared with that obtained from a new model that has been developed for computing array gain in resolved noise. Both models indicate that substantial detection gains are possible with large-aperture arrays when individual ship interferers are resolved.