### 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.