Signal processing techniques for low-order acoustic modes

Abstract

Internal waves introduce substantial fluctuations in the lowest mode signals recorded during long-range tomography experiments. Lacking a complete random model for the mode signals, tomographers typically resort to averaging the mode signals across receptions to mitigate internal wave effects. Chandrayadula et al. used the 2004 Long Range Ocean Acoustic Propagation EXperiment (LOAPEX) signals and parabolic equation (PE) simulations modeling the LOAPEX environment to derive range-dependent statistics such as temporal mean, temporal covariance, and intermodal correlation of the lower mode signals [Chandrayadula et al., J. Acoust. Soc. Am. 120, 3062 (2006)]. This talk proposes several statistical signal processing techniques such as likelihood ratio detectors, minimum entropy deconvolution methods, and empirical orthogonal function detectors that are based on the derived statistics, to mitigate internal wave effects. The proposed methods are tested on both the LOAPEX signals and PE simulated mode signals and compared against simple averaging techniques. [Work supported by ONR.]