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Sonar Model Based Matched Field Signal Processing

Passive underwater sonar array systems were subject to development in the past decades for accomplishing tasks in naval surveillance and geo-acoustical investigation of the ocean bottom. Modern sonar passive array systems are using adaptive matched field signal processing techniques. Passive sonar array signal processing based on ocean physical propagation model is known as “Matched Field Processing” (MFP). It is a specific application of the more general case of space-time adaptive signal processing in the area of sonar array signals processing (Klemm, 2002). It is a cross-correlation technique developed for matching the values of the computed with a propagation model sound pressure with the measured values at the output of a passive sonar vertical array. The maximum in the crosscorrelation or ambiguity surface gives an estimation of the position of the underwater source. This technique is first proposed by Clay in 1966 and later on theoretically and experimentally developed by Hinich and Bucker in 1972 and 1975 (Sullivan & Middleton, 1993). In 1980 and 1981 Klemm introduced in the matched field signal processing algorithms the Capon’s minimum variance and Burg’s maximum entropy estimators for better resolution in shallow water environments (Sullivan & Middleton, 1993). The acoustic field in an ocean horizontally stratified waveguide may be presented as a sum of “normal waves” or “normal modes”1, each satisfying the boundary conditions and propagating down the layer with its own speed, wave constant and attenuation. The coherent modal sum is used in matched field signal processing for localization of an underwater source in range and depth. It can be used for localization of the source also with a horizontal array because the angular modal spread is proportional to the direction of arrival relative to the axis of the array (Klemm, 2002). The matched field processing for source position localization is presented in most of the investigations as a parameter estimation problem. It is assumed that the detection has been carried out and the frequency of the source is known. Some authors consider joint detection and localization problem [Booth et al., 2000]. In the beginning MFP of narrowband signals was used which was later modified with the more realistic for practical applications broadband case where MFP results for several frequencies are averaged. The aim of this chapter is to introduce the reader to the principles of matched field signal processing and present narrowband MFP experimental results. An available on the web normal mode propagation code and vertical sonar array signals data from a controlled source localization experiment are used. A comparison is made between MFP