Acoustic diver deterrent in a shallow harbor using time reversal acoustics

Protection of domestic harbors against surface and underwater threats is an important task of port security. A significant security risk is associated with scuba divers ability to carry explosives. The diver detection sonars have been developed and there is a need to compliment it with low cost acoustic swimmer deterrent. Previous research demonstrated that time reversal acoustic (TRA) system can focus intensive sound using acoustic noise from a diver. This paper discusses the feasibility of applying TRA principles for the focusing of sonar ping-pulse reflected from a diver. The advantages of the TRA focusing system and relevant operating parameters are demonstrated using the model of shallow sea, where propagation of sonar pulse is affected by numerous reflections from surface and bottom. The developed model was used to estimate and compare an effective zone of the diver deterrence taking into consideration the sonar pulse reflections from diver, bottom and surface. The main objective was to estimate if NAVY ship sonar is capable of producing sufficient and spatially localized sound pressure to disorient and divert the diver away. A secondary objective was to ensure that sound pressure level outside the focal zone in the diver proximity remains not harmful to marine life.