Shallow grazing angle sonar detection of targets buried under a rippled sand interface

A laboratory-type measurement was conducted to investigate shallow grazing angle acoustic detection of targets buried in sand having a rippled sediment-water interface. The measurement was performed in a 12.2-m deep, 110-m long, 80-m wide test pool, which has 1.5 m of sand covering the bottom. In this measurement, broadband, broad-beam transducers were placed on the shaft of a tilting motor. In order to reduce the masking effects of bottom reverberation, the transducers and tilting motor assembly were attached to a rail that permitted this assembly to be translated horizontally, enabling an array to be synthesized with a larger effective aperture than the physical array itself. A silicone-oil-filled target sphere was buried under a rippled interface, which was artificially formed with the aid of a sand scraper that consisted of a frame and a "rake" that glided along the frame. Acoustic backscatter data were acquired in the frequency range of 10 to 50 kHz for acoustic propagation perpendicular to sand ripples having a 50 cm wavelength. Shallow grazing angle detection results are compared to model predictions that use measured surface topography.