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Subcritical detection of an elongated target buried under a rippled interface

This paper describes recent results from an ongoing measurement and modeling effort investigating shallow grazing angle acoustic detection of targets buried under a rippled bottom. The measurements are being performed in a 13.7-m deep, 110-m long, 80-m wide test-pool with a 1.5-m layer of sand on the bottom. The rippled bottom is formed by scraping the sand with a machined rake. A parametric sonar (1 to 20 kHz) and broad band (10 to 50 kHz) transducers are placed onto the shaft of a tilting motor, which in turn is attached to an elevated rail that enables this assembly to be translated horizontally, permitting acquired data to be processed and displayed as images. Data acquired with the broad band transducers could be further processed using synthetic aperture sonar (S AS) techniques. In previous work, measured calibrated backscatter levels obtained from a buried silicone oil-filled sphere were compared to predictions of a model that uses perturbation theory. Most of the data-model comparisons exhibited good agreement (Lopes et al., "Subcritical Detection of Targets Buried Under a Rippled Interface: Calibrated Levels and Effects of Large Roughness," MTS/IEEE, pp.485-493.). In order to evaluate model predictions on more complex scatterers, an additional series of measurements was conducted using an elongated cylindrical shaped target that was buried under the rippled surface. Images of the buried cylindrical target were generated and are presented. Also presented are signal-to-noise ratios of the buried target