High frequency marine mammal mitigation active sonar system

The High Frequency Marine Mammal Mitigation (HF/M3) sonar system was specifically designed to meet the marine mammal mitigation plan proposed by the Surveillance Towed Array Sensor System Low Frequency Active (SURTASS LFA) Draft Environmental Impact Statement. The system is integral with the SURTASS LFA, residing at the top of the vertical transmit array, utilizes PC based processing and control, and is comprised primarily of commercial off-the-shelf (COTS) components. The HF/M3 is an active sonar operating in the 30-40 kHz frequency range. The system utilizes four independent transponders mounted on a rotating carousel. Each transponder consists of an omni-directional hydrophone located at the focal point of a 12"/spl times/18" air-backed, parabolic reflector. The reflector provides for an on-axis transmit and receive directivity factor of 20-25 dB to depths of 1000 ft. The system has been tested in numerous field trials, where its ability to detect marine mammals of various size has been qualitatively verified. Quantitative performance estimates, generated using empirical interference and target echo models, suggest that a single, moderately-sized (/spl sim/5 m in length) marine mammal swimming radially toward the system has less than a 1 in 1000 chance of penetrating the LFA's designated 180 dB re /spl mu/ Pa/sup 2/ isoplath.