Acoustic detection of targets buried at steep and subcritical grazing angles

A very shallow water measurement was conducted to investigate acoustic detection of targets buried at steep and subcritical grazing angles. The measurement was performed at a sandy bottom site in approximately 3.05-m water depth in St. Andrew Bay in Panama City, FL. A 25-cm. diameter partially populated acoustic lens based system was employed as the source and receiver. The sonar was attached to a 1.68-m high stationary sonar tower complete with horizontal pan and vertical tat motors. Calibrated retro-reflectors and silicon oil filled spheres were used as the buried targets. Data were acquired in the frequency range of 25 to 55 kHz for grazing angles that varied from about 5/spl deg/ to 35/spl deg/. Detection results corresponding to targets buried at steep grazing angles are compared to a simple sonar performance model. This simple model is also used to predict performance for various sonar configurations (frequency and aperture size). Results of sonar capability against targets buried at subcritical grazing angles are presented and compared to results obtained in earlier very shallow water measurements as well as to results reported in the literature.