Acoustic field coherence in four-dimensionally variable shallow water environments : estimation using co-located horizontal and vertical line arrays

Abstract

The implementation of two- and three-dimensional acoustic receiver arrays is challenging in the ocean environment. Fixed geometry and connectivity can only be built and maintained at great expense. However, such ideal arrays can be very powerful for signal detection, classification, and tracking, although many of the signal-processing methods employed are subject to constraints of acoustic field temporal and spatial coherence. Thus, understanding the processes at work determining coherence is essential because system effectiveness may then be predictable from environmental parameter input. To study acoustic fields and coherence over finite aperture, the research community has recently taken steps to enable routine use of co-located horizontal and vertical line arrays, typically arranged in the shape of the Roman letter L (or Greek ð€€ª ), with the horizontal leg on the seafloor. This is a small subset of all possible geometries, but it enables measurements of acoustic field coherence not possible with single line arrays. Here, new L-array measurements made in the SW06 field program are used to measure coherence and test coherence predictions via joint analysis of vertical and horizontal line array receptions. Impulsive mode arrivals (including mode multipath) from fixed sources will be estimated using the vertical array. Signals on the horizontal array, which is neither broadside nor endfire, will be compared with signals synthesized using the mode arrivals to estimate azimuthal decorrelation effects. Results can be compared with coherence estimates from computational and theoretical studies.