Buried object scanning sonar

A sonar, designed to scan for objects buried in the seafloor, generates images of pipe and cable sections and ordnance buried in sand. The sonar operates by illuminating a broad swath of the seabed using a line array of acoustic projectors while acoustic backscattering from the illuminated sediment volume is measured with a planar hydrophone array. The line transmitter performs along track beamsteering to improve the SNR of buried target images by illuminating major target surfaces at normal incidence and to reduce volume scattering by limiting the volume of sediments illuminated. The output of the planar-hydrophone array undergoes nearfield focusing which allows the sonar to operate near the seabed where target images have the highest SNR and resolution. The nearfield focusing reduces scattering noise by approximately 12 dB, an improvement measured by comparing the SNR of target echoes in single channel data with the SNR of buried targets in the focused imagery. Plan and side views of the seabed generated from a three-dimensional matrix of focused data provide the position and burial depth of targets covered by sand off Hawaii. An energy detector automatically locates targets in the focused image data