Experimental demonstration of sound-speed inversion with matched-field processing

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 environment’s sound-speed profile by matching predicted and measured amplitude and phase. Simulations and an initial experimental demonstration of the power of the technique are based on a modified version of Munk’s canonical sound field model. This model is used in a simulated environment with a 15-Hz source where source and receiver locations are known. The simulation demonstrates that changes in the depth and strength of the modeled sound channel axis directly result in trackable errors in range and depth as well as in reduction of the received power level. The same model is used to determine sound-speed profile using a 15-Hz signal from a 244-m explosive source detected on a 675-m vertical array at a range of 53 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. For the single test case, resultant differences between the matched-field 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.