On the response of a towed array to the acoustic field in shallow water

A theoretical treatment of the response of a towed array to the acoustic field from a point source in isovelocity shallow water is presented. The analysis, which is based on a wave-theoretical representation of the field, reveals several interesting effects when the source is endfire-on to the array. Beam broadening or beam splitting may occur due to the distribution of the modal energy in elevation, a feature which also leads to signal rejection by the array. The latter phenomenon is characterised by a signal gain which, in general is less than the directivity index of the array. Other aspects of performance which are addressed include the effects of range averaging, the dependence of the output on the source-depth/receiver-depth combination, and the noise gain of the system when the limit to the signal/noise ratio is set by wind-generated ambient noise.