Sound‐speed determination using matched field processing techniques

Abstract

Matched field processing is shown to be effective for estimating sound speed in a deep, range‐independent ocean environment. The amplitude and phase of signals from a distant source measured on a large aperture vertical array are sensitive to changes in sound speed. This sensitivity is exploited to infer the environmental sound‐speed profile by matching predicted and measured amplitude and phase. A sound‐speed profile model is developed based on a modified version of Munk's canonical sound field equation. This model is used to determine sound‐speed profile using a 15‐Hz signal from a 240‐m explosive source detected on a 675‐m vertical array at a range of 50 km in a deep‐water Pacific environment, characterized by a classical range‐independent sound channel at 700 m. The search for the best estimated profile is conducted by varying the sound channel axis strength and depth in the modified Munk equation while maintaining a constant sound‐speed profile at great depths. Differences between the estimated and measured profiles are less than ± 2 m/s; the sound channel axis depth is determined within 20 m of the measured axis depth. Extension of this approach to include mesoscale features and greater range is discussed.