Experimental investigation of optical, remote, aerial sonar

Detecting underwater objects such as debris fields, submarines or mines for littoral area clearance, while in the air, would increase the autonomy and flexibility of subsurface, surface and air vehicles engaged in undersea warfare and could have a variety of commercial and oceanographic applications. Experimental research into a laser-based active sonar concept is being conducted for remote, aerial detection of submerged objects and for sonar mapping of an undersea area. An airborne high-energy, pulsed laser is used to remotely generate underwater acoustic energy. The acoustic wave propagate through the water and are reflected from underwater objects. The acoustic signals are then detected as they reach the water surface using a low-powered laser interferometer device. An array of surface detections of the acoustic field reflected from the underwater objects will then be analyzed using traditional time-delay beamforming techniques to locate underwater objects. The combination of these optical technologies provides a means for stealthy, remote, active as well as passive sonar that does not currently exist. Results are presented from a controlled laboratory test using commercial laser devices, which demonstrate the feasibility of the sonar concept for remotely searching for underwater objects. This paper outlines the aerial sonar concept and provides the initial experimental results of the underwater object illumination, detection and localization.