Mid-Frequency Sonar Backscatter Measurements from a Rippled Bottom

摘要

Seafloor ripple reverberation is associated with a peak in the scattering frequency spectrum at a frequency around c/(2λr cos θ), where c is the sound speed in water, r is the ripple wavelength, and θ is the incident grazing angle. In the vicinity of this peak, perturbation theory predicts the reverberation level to be high enough to be a concern for detection of targets buried under ripple. In order to validate such predictions, an experiment was conducted in the Naval Surface Warfare Center Panama City (NSWC-PC) Facility 383, which is a 13.7-m deep, 110-m long, 80-m wide test pool that has 1.5 m of sand covering the bottom. Backscatter reverberation levels from two bottom configurations were measured using a parametric source that was operated in the 1 to 10 kHz frequency range. One bottom configuration corresponded to a non-rippled, near-flat bottom. The second was a rippled bottom with a Gaussian spectrum centered on a wavelength of 20 cm. The rippled bottom was artificially formed with the aid of a sand scraper. Results showed the reverberation levels were significantly higher in the 3 to 5 kHz frequency range for the rippled bottom than for the non-rippled bottom. The maximum reverberation level for the rippled bottom occurred at 4 kHz, which is consistent with perturbation theory predictions.