The two-dimensional multibeam echo integration (2DMBEI) method, which provides the user with the target strength of a fish school, was derived analytically based on the theory of three-dimensional multibeam echo integration. It was developed to establish a reliable and practical methodology of fish abundance assessment using scanning sonar for fishery use. The 2DMBEI method was implemented in the data analyzing software of a quantitative scanning sonar system. Furthermore, a sea experiment using tungsten carbide spheres simulating a fish school was conducted to validate the 2DMBEI method.
The Japan Agency for Marine-Earth Science and Technology is developing an automatic bottom inspection and sampling mobile (ABISMO), which is a full-depth rating ROV (Remotely Operated Vehicle) for reaching to the deepest sea bottom, observing it with a camera and sampling the bottom layer. ABISMO consists of a launcher and a vehicle. The launcher is a kind of depressor with many observation devices, and the vehicle is an underwater crawler to move on the sea bottom and inspect it. The mother ship can determine the vehicle's position directly with the ultra-deepwater transponder. The transponder is small and lightweight, with a release system, and it operates at about a 14-kHz frequency. The frequency is higher than that of a conventional full-depth transponder, and it features greater navigation accuracy in shallow water, where many ROV do most of their work. These advantages are emphasized when the transponder is loaded onto an ultra-deepwater vehicle, which needs to be small and lightweight.