Normal mode wave-number estimation using a towed array

In the analysis of the null-steering technique of normal mode filtering presented by the authors previously [H.M. Chouhan and G.V. Anand, J. Acoust. Soc. Am. 89, 735-44 (1991)], it was assumed that the modal wave numbers km are known a priori. In practice, the waveguide parameters upon which the modal wave numbers depend are normally not known and are difficult to measure accurately. In order to use the null-steering technique of mode filtering, or in applications such as source localization and waveguide characterization, it is necessary to estimate the modal wave numbers. An estimation procedure using a towed horizontal line array is presented. The method entails eigendecomposition of the range-averaged array signal correlation matrix. Range-averaging effectively decorrelates the normal mode signals and enables the use of high-resolution spectral estimation techniques such as MUSIC for estimating the modal wave numbers. Simulation results for the Pekeris model of the ocean are presente