System for mono- and bistatic sonar investigation of buried objects

Within the SITAR-project, a system for studying small objects in or on the bottom, has been developed. It uses a parametric sonar and hydrophones mounted on an ROV, and a vertical chain of hydrophones placed on the bottom. A commercial acoustic positioning system, consisting of four transponders anchored to the bottom and a transceiver mounted on the ROV, was used. To avoid acoustic interference it was found necessary to synchronize the sonar and the positioning system. For this purpose a PC-program, intercepting the serial communication to the positioning system, was developed. The man-machine interface of the ROV was implemented as a Visual Basic program on a PC. A major challenge was to keep track of the ROV, the sonar lobe, the hydrophone chain and targets in or on the bottom. To solve this problem a navigation- and aiming program was developed in Visual Basic. This program supports searching for targets in monostatic mode, positioning of the hydrophone chain as well as bistatic measurements on a selected target. The pitch- and course angles of the ROV can be controlled from the navigation program making it possible to keep the sonar lobe locked to the target while the ROV moves around it. The navigation program also logs position data to a disk file. Data from the hydrophone chain and the hydrophones on the ROV were collected on a separate system and presented in real-time.