Oceanic tomography using model‐based matched‐filter processing of wideband acoustic signals

Abstract

As originally conceived, ocean acoustic tomography relies on determining the travel times of pulses that propagate along identifiable multipaths between pairs of transducers. In principle, other properties of acoustic propagation such as amplitude and phase over a broad frequency band can be used to infer environmental parameters. These parameters include range‐dependent sound‐speed profiles and geoacoustic parameters of the sea bottom. Recent experimental work has demonstrated that the distortion of time‐dispersed wideband signals can be compensated effectively by using a model‐based matched filter (MBMF). A multi‐channel MBMF receiver that incorporates the modeled Green’s function of the medium, determined the correct range and depth of the source and receiver. In this paper, the possibility of applying model‐based matched‐filter processing to the tomographic inversion problem was investigated. The acoustic data are low‐frequency, large time‐bandwidth product, linear‐frequency‐modulated signals transmitted through a range‐independent waveguide at a deep water site west of Sardinia. Compared to time‐of‐flight tomography, the amplitude and phase distortion undergone by the propagated waveforms were fully exploited to reconstruct, in part, the range‐averaged sound‐speed profile between source and receiver. This was achieved by searching for the set of sound‐speed profile parameters that maximized the gain at the output of a multi‐channel MBMF receiver.