Computing ship resolution gain for horizontal towed arrays in realistic ocean environments

Previous experimental measurements of beam noise have shown that spectrum levels measured with towed line arrays have considerable temporal and spatial variability. In the ambient noise region dominated by shipping noise (a few Hz to a few hundred Hz), variations in spectral levels of over 30 dB can occur. Attempts to model the predicted beam noise cumulative distribution function (R.M. Heitmeyer, L.T. Davis and N. Yen, NRL Report 8863, February 1985) required approximations for both the beam pattern and transmission loss to achieve an analytic solution. The computed detection gain in regions of reduced noise resulting from resolution of individual noise-interferers, termed “ship resolution gain” (SRG), is dependent on source distribution, acoustic transmission loss and beam pattern approximation. The paper uses numerical computation of SRG to treat arbitrary hydrophone shading and realistic ocean environments. Results are compared to earlier analytic predictions to show dependence on system and environmental parameters