Surface Wave, Internal Wave, and Source Motion Effects on Matched FieldProcessing in a Shallow Water Waveguide

摘要

Given known environmental conditions, matched field processing is shown to be apromising signal processing technique for the localization of acoustic sources. When environmental data are incomplete or inaccurate, a mismatch occurs between the measured and model fields, leading to a severe degradation of the localization estimator. The possible mismatch effects of surface and internal waves on matched field processing in a shallow water waveguide were investigated. A modified ray theory will calculate the acoustic pressure field. Range dependent environmental conditions were incorporated to generalize this work to deeper waveguides. The conventional matched field beamformer does not provide sufficient resolution to unambiguously locate a source, even in a perfectly matched environment. The maximum likelihood method matched field beamformer has much better resolution, but is very susceptible to mismatch. The mismatch due to surface roughness can result in a large reduction of the estimator peak. Part of the peak is regained by using a model including incomplete reflection at the surface based on actual sea surface statistics and short time averaging of the measured signal, with times on the order of the period of the surface waves. Mismatch due to internal waves can result in a large degradation of the estimator. Averaging over the same time period as surface waves provides little improvement leading one to surmise that internal waves may be a limiting constraint on matched field processing. The surface and internal wave fields were combined with a slowly moving source, which highlights the necessity for the development of a beamformer with a broader mainlobe while maintaining adequate sidelobe suppression. (jhd)