D. W. Craig
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.