Sparse broadband time varying acoustic response modeling and estimation from an undersampled vertical array with application to underwater communications.

Abstract

Sparse broadband time varying acoustic response functions associated with horizontally stratified environments can be well estimated from an undersampled vertical array. The sparsity of the arrivals here is captured by means of a two component Gaussian mixture model. The implied posterior expectation of the bifrequency function serves to attenuate low amplitude non-coherent arrivals while leaving coherent arrivals at the array unchanged. This estimate of the acoustic response specifies a time varying increment operator that unravels the time varying motion between the source and receiver array allowing for a further sparsification of the response. This additional improved sparsity allows for improved coherent multipath combining at the receiver. The model is applied to a three element vertical array during a set of broadband acoustic observations in the shallow waters of Buzzard's Bay, MA. M-ary orthogonal spread spectrum acoustic transmissions at 32.5 kHz center frequency and 25 kHz bandwidth are considered. With M = 4, throughput rates of 95 bps are tested. At 2 km and at a receive signal-to-noise ratio per element of -15.5 dB, a 3 element undersampled vertical array achieved bit error rates less than 10-5.