Shallow water reverberation measurement and prediction

Abstract

Low frequency active sonar performance in shallow water is often limited by reverberation. Reverberation modeling in shallow water has been difficult due to the complexity of the multipath acoustic propagation problem inherent in shallow environments. In August 1992, a shallow water, low-frequency reverberation measurement was made in the Barents Sea utilizing explosive signal, underwater sound (SUS) charges as sound sources and a 16-element vertical hydrophone array as the receiver. The objectives of this thesis were to analyze the reverberation data from this experiment, compare several theories which have been proposed to model reverberation, and determine the reverberant characteristics of the region. The three-dimensional Hamiltonian Acoustic Ray- tracing Program for the Ocean (HARPO) was used as the primary propagation modeling tool. The temporal signal processing consisted of a short-time Fourier transform spectral estimation method applied to data from a single hydrophone. Chapman's source spectrum model was used. Reverberation models based on Lambert's law and omnidirectional backscattering theory were compared. Lambert's law was found to be more applicable in the Barents Sea. A statistical analysis was performed on broadband and narrowband hydrophone data showing that reverberation in the Barents Sea possesses Gaussian properties