FAST BISTATIC SIGNAL-TO-REVERBERATION-RATIO CALCULATION

Abstract

Closed-form expressions are presented for signal and reverberation in a wide variety of bistatic scenarios including variable bottom bathymetry. These extend the findings and inferences from already published expressions for monostatic sonar and provide considerable insight into sonar performance. They are also developed into a hybrid numerical solution that can be applied to realistic grided environments (though isovelocity so far). Derivations are based on an eigenray sum with (bistatically varying) Lambert's law scattering, and the result is valid for general smoothly varying bathymetry. Examples of reverberation, target echo, and signal-to-reverberation-ratio (SRR) are given for the case of a uniformly sloping bottom abutting a shelf. The SRR is always high immediately behind the receiver (i.e. in the opposite direction from the bistatic source). Conversely the SRR is very poor between the source and receiver. An example of the hybrid numerical approach with realistic bathymetry from the area in between Sicily and Malta shows that Lambert's law with "mode-stripping" lead to high detection ranges. Noise limiting moderates this and there is then a roughly elliptical annular region with high SRR; inside and outside the annulus performance is poor. Calculating a full set of plots takes only a few seconds on a PC and requires no priming or tabulation. Therefore sonar assessment of complete moving scenarios becomes a practical proposition.