Modal matched‐field processing with small aperture vertical arrays

Abstract

In the past years, much attention has been given to mode space matched‐field processing in shallow‐water, low‐frequency environments. In this type of situation, mode space matched‐field processing has several advantages over conventional matched‐field processing such as: lower processing dimension, better sidelobe rejection, and the ability to discriminate signal against modal noise. However, extraction of modal amplitudes from data by the method pioneered by Shang [J. Acoust. Soc. Am. 77, 1413–1418 (1985)] is not very reliable for small aperture arrays. Attempts have been made to overcome this problem in order to make mode space matched‐field techniques more applicable to actual physical environments [T. C. Yang, J. Acoust. Soc. Am. 82, 1736–1745 (1987)]. A fresh approach is brought to this problem here using computer simulations of matched‐field processing in a Pekeris waveguide to demonstrate a new method for extracting modal amplitudes from data. These simulations demonstrate that this new method of modal amplitude extraction allows successful mode space matched‐field detection and localization at array apertures significantly smaller than those allowed by previously used algorithms. Finally, the algorithm will be discussed in the general context of dimensional reduction techniques.