Comparison of measured buried target backscatter levels with high-order predictions: Rippled interface effects

Abstract

Controlled sonar measurements with buried spheres and cylinders have demonstrated diffraction by bottom ripple can significantly improve target detection performance with sonar operated at grazing angles shallower than the critical grazing angle. Furthermore, buried target scattering models based on low-order perturbation theory to handle sound transmission through bottom roughness confirm that a significant enhancement in detection performance can be expected. But comparisons between measurements and model predictions have not always produced good agreement. As the bottom ripple height increases, discrepancies have been noted in comparisons with the predicted backscatter levels from a buried sphere, suggesting a failure of low-order perturbation theory to properly account for high-amplitude roughness effects. Recently, a recursive algorithm to generate arbitrary-order perturbation corrections for transmission and reflection through an idealized sinusoidal ripple was formulated and incorporated into our existing buried target scattering codes. The resulting higher-order predictions indicate previous discrepancies were not necessarily due to the neglect of high-order corrections. Calculations show model inputs such as bottom attenuation can influence backscatter levels significantly and measurement of these parameters may need to be performed more carefully. We demonstrate this through a presentation of data and model comparisons. [Work supported by ONR and SERDP.]