Target echo and clutter calculations, including time spreading using normal-mode group velocities.

Abstract

The shallow-water normal-mode reverberation approach [D. D. Ellis, J. Acoust. Soc. Am. 97, 2804–2814 (1995)] can be extended to handle the echo from a target or discrete clutter objects. Normal modes are used to handle the propagation, and ray-mode analogies are used to handle the echo and scattering. The time spreading of the echo can be approximated using the modal group velocities. This description for the time spreading is approximate, but the computations are quite efficient, since the normal modes need only be calculated at one frequency. The target can be point-like and mode functions can be used, or the target can be considered more extended and the mode amplitude envelopes can be used. The formulation will be presented, along with a number of calculations based on problems from the ONR Reverberation Modeling Workshops. [Work supported in part by ONR, Code No. 321OA.]