Robustness and constraints of high-frequency ambient noise inversion for sonar performance estimation

Abstract

Perhaps the most dominant source of error in sonar performance estimation in shallow waters is the geoacoustic description of the seafloor. Various investigators have studied the possible use of ambient noise to infer some key parameters such as the critical angle, geoacoustic properties, or bottom loss. Most operational sonar performance models and tactical decision aids require the bottom loss as a function of grazing angles and frequency to describe the reflected acoustic energy off the ocean floor. Harrison and Simons [Harrison & Simons, ‘‘Geoacoustics inversion of ambient noise: A simple method,’’ J. Acoust. Soc. Am. 112, 1377 (2002)] described a simple measurement approach to infer the bottom loss from ambient noise measurement on a vertical line array. This approach is well suited as an environmental measurement approach during naval operations. The robustness and operational constraints of this measurement approach are quantified using a high-frequency ambient noise model that accounts for wind, shipping, and thermal noise [Ferat & Arvelo, ‘‘Mid-Frequency Ambient Noise Directivity And Array Response in Range-Dependent Environments,’’ High-frequency Ocean Acoustics Conference Proceedings, 2004)]. The effects of array tilt, nearby shipping noise, water absorption, thermal noise, surface-noise dipole pattern, and array beam response on sonar performance estimation are demonstrated. Mitigating factors to maximize estimated bottom loss accuracy will also be outlined.