Synthetic aperture processing of buried object scanning sonar data

Synthetic aperture processing improves the resolution and signal to scattering noise performance of buried object scanning sonar (BOSS) imagery. Time delay focusing coherently sums acoustic data measured by a line hydrophone array located in the wings of the BOSS vehicle. Synthetic aperture processing improves the along track spatial resolution by coherently summing the data over a sequence of transmissions. SAS (synthetic aperture sonar) motion compensation is implemented by calculating the changes in projector and hydrophone positions between transmissions using IMU (inertial measurement unit) and DVL (Doppler velocity log) data. The coherent summation is performed at each location in a 3D volume of focal points including the upper meter of sediments and the sediment-water interface. Sonar images are projections of the 3D data set onto orthogonal planes. A set of three cylinders with diameters of 5,7.5 and 10 cm, buried in sand, are used to measure the relationship between SAS aperture length and the SNR and spatial resolution of BOSS imagery. The BOSS data sets containing the cylindrical targets were collected in September 2004 as part of SAX-04 (Sediment Acoustics Experiment - 2004), located off Fort Walton Beach, Florida.