Army Combat Helicopter (AH-1W) crashed in Techi Reservoir, located in a high mountain at about 1500m. The water depth where the helicopter is located is about 75 m, and the water temperature is about 13°C. Due to the alpine climate and the deep water depth is deep diving (the water pressure is still only about one atmosphere per 10 meters, so the difficulty of this search and rescue and salvage operation is increased. Since the helicopter crash, with the full cooperation of domestic academic institutions and the military. First use the side scan sonar to obtain the scanning images of the helicopter. Then use the unpowered underwater camera and the underwater remote control vehicle to capture a small number of images of the crashed helicopter. But it is still impossible to repeatedly search for the helicopter body within the range of 150m×150m wreckage. 

        Multibeam sounding system is the best choice in this environment. Our working group uses real-time DGPS positioning system with multi-sound beam sounding system. Not only accurate coordinates can be obtained, but also image maps, stereograms, etc. can be drawn from the obtained high-density water depth data (figure 1). Various layers drawn by the multi-beam sounding system. After researching and judging that the bow and stern of the helicopter are indeed grasped, the exact point coordinates of the bow will be provided to the remotely operated vehicle (ROV) search team for search. Due to the extremely low visibility, after searching for some debris, I finally lived up to expectations and found the position of the bow (the main body of the driver's seat). Immediately fix this place with a steel cable, and then the military and private salvage companies will carry out salvage matters. In the end, the helicopter was successfully salvaged ashore. It fully demonstrates the importance of technical integration, and also demonstrates the advantages of multi-sound beam sounding system in underwater search.

AH-1W Helicopter Image Map of Techi Reservoir measured by Multibeam sounding system (left) and stereogram (right). the upper right corner is the schematic diagram of AH-1W.