Wavefront curvature and near‐field corrections for scattering by targets buried under sea‐floor ripple.

Abstract

Curvature of the incident field wavefront has been implicated in discrepancies between modeled and measured pressure fields scattered at shallow grazing angles from targets buried under ripple in NSWCPCD’s test pond, where the range to the target is limited to about 10 m. Improvements on our attempts to correct for these and other near‐field effects in existing incident‐plane‐wave‐based models is described here. Explicit numerical integration of incident field expansion coefficients as well as the basis functions needed to formulate the transition matrix solution for the scattering process is used in order to create a reliable benchmark for comparisons with simpler corrections and measured data. It is found that some care must be exercised in performing the required two‐dimensional wave vector integrals because the ripple wave vector can cause integration to be unstable in the perturbative terms accounting for ripple effects. Results are compared with recent modifications of existing sonar simulations and data collected in NSWCPCD’s test pond. [Work supported by ONR and SERDP.]