Abstract Recovery of underwater drowned human body is one of the major missions of the firefighters. However, due to short of man power, lack of training and professional equipments, this kind of body recovery mission was basically conducted on the shore and at the water surface. Only a limited amount (if any) of diving activities were conducted to search for the drowned body. For a much more efficient way to conduct this kind of body recovery activity, it is necessary to incorporate the state of the art of the underwater acoustics technique, such as scanning sonar, into the operation procedures. Underwater stationary targets are objects sitting on the seafloor that can¡¦t move autonomously. Apparatus feasible for the detection of these underwater stationary targets includes: optics, acoustics and geophysical instruments. Among them, acoustical apparatus is the most feasible one. The purpose of this research was to investigate the application of scanning sonar for underwater human body detection and recovery. Based on theoretical considerations, the use of scanning sonar can improve both total time consumed and target detection rate of body recovery rescue activities. Three real cases which incorporated this equipment into the rescue work illustrated that the movement of a diver, several suspected targets and the morphological features around the targets can be recognized by the scanning sonar. In addition, the dimensions, shapes, amount and geographic locations of the targets can be identified for further considerations. During the mission at the Jih-Yueh-Tan Reservoir, it was proved indirectly that the scanning sonar can detect the drowned human body successively. Based on this investigation, it is recomended that the detection and identification ability of the scanning sonar can be dramatically improved if optical apparatus such as ROV (remotely operated vehicle) or TOV (towed operated vehicle) was incorporated into the operation procedures.

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Search for drowned human body by divers is a highly technical dependent, difficult and dangerous work. How to improve this kind of underwater rescue work, under the considerations of the safety of divers and the effectiveness in detection of the target within a limited period of time, is a major subject for fire fighters. For the time being, a normal search and rescue procedure basically includes visual observation of the bank area and surficial water area. In addition, divers are sometimes sent out to complement the search procedure by either visual observation or tactile. A much more efficient way to conduct this kind of recovery activity is to incorporate the state of art of the underwater acoustics technique, such as scanning sonar, into the operation procedures. This investigation was focused on the application of scanning sonar and image analysis techniques as well as seafloor object identification skills for the detection of drowned human body. In addition, safety of divers under water and their activities could be improved and monitored. Remotely operated vehicle (ROV) and towed operated vehicle (TOV) should be incorporated into the normal search procedure for the purpose of improving target identification in the future. Under this circumstance, both target searching rate and divers¡¦ safety could be effectively improved or guaranteed. The proposed procedure which incorporated both acoustical (i.e., scanning sonar) and optical (i.e., ROV or TOV) apparatus are expected to simplify and improve the underwater target search and identification activities and will allow fire fighters a more professional and safety way in conducting drowned human body recovery activities.