Modeling of the influence of the self noise on the array gain of a sonar system

The detection performances of an underwater acoustics detection system such as a sonar, can be reduced by self noise phenomena. In this paper, it is shown that the definitions of the noise and array gain terms in the sonar equation are related one to the other, and special attention has to be paid to the choice of the reference sensor. A formalism is introduced to take rigorously into account the self noise in the array gain, by splitting the effects of ambient and self noises. The consistency of this formalism with theoretical and experimental results is checked using case studies. For example, it is shown that for a bow-mounted array inside a sonar dome, the array gain behaves like the directivity index, as for a flush-mounted flank array the assumption of uncorrelated noise is more realistic.