Active invariance structure in deep water towed array data.

Abstract

The concept of a waveguide invariant has been used extensively to explain and exploit the time‐frequency structure present in passive lofargrams. Recently this concept has been extended to active sonar data and has been demonstrated experimentally for both target and bottom scattering returns obtained in shallow water channels. In this talk, characteristics of the active invariance structure observed with towed horizontal arrays operating in deep water channels are presented and discussed. A towed array offers an ideal array aperture to observe the active invariance structure because a single pulse received across the array can be processed to recover the invariance striations. This processing offers higher resolution than what would be obtained with multiple returns from a moving target when sampled across a single receiver. Furthermore, for larger apertures operating at higher frequencies, the ability to observe the invariance intensity structure may be affected by details of the beamforming. The framework for towed array invariance processing is presented theoretically and illustrated with data obtained from a towed array operating in a deep water environment. As expected, the values for the deep water invariant differ from shallow water in both magnitude and sign.