Monostatic and bistatic reverberation results using linear frequency-modulated pulses

Abstract

Estimates of reverberant scattering strength are presented as a function of range and bearing for selected monostatic and bistatic geometries of a reverberation experiment. Diffuse scattering strengths were found to be comparable (within ∼3 dB) for both monostatic and bistatic geometries. This experiment was performed off the west coast of Sardinia in approximately 2800 m of water during February of 1990. The receiver was a horizontal array of approximately 20 wavelengths. Source and receiver depths ranged from 50 to 120 m. The signals used consisted of linear frequency-modulated (FM) pulses centered near 1 kHz with durations ranging from 8 to 16 s and bandwidths ranging from 32 to 64 Hz. Monostatic and bistatic scattering strength values are estimated using uncorrelated (i.e., not match-filtered) pulses. The scattering strengths presented vary from −29 to −48 dB for ranges up to 40 km (but not data near fathometer returns). A method is described that shows different correlator gains against noise and reverberation. Comparisons of measured and modeled reverberation are presented using the generic sonar model (GSM) and curve fits with the decay in monostatic diffuse backscatter show good agreement with Lambert’s rule using a −32 dB constant. Finally, GSM is used to estimate grazing angles from which plots of measured scattering strength versus grazing angle in the 10°–26° interval are presented. Using this method, a Lambert’s rule constant of ∼−30 dB was a better fit to the data.