Remotely Operated Vehicles (ROVs) equipped with underwater video cameras are often used to conduct Visual investigations such as observing fish behavior. It is, however, Very difficult to guide an ROV to its target Without the aid of an accuracy positioning system. Therefore, We have developed an ROV positioning system using an ultrasonic pinger, Which presents a highly accuracy real time track pIot. A pinger is an underwater ultrasonic tag, Whose bearing can be determined from the directivity of a directional transducer, and the distance from the transducer to the pinger is inferred from the amplitude of the received pulse. The positioning accuracy in such cases however, is unreliable. In this study, the distance from the transducer to the pinger is calculated by using an original method in which the receiver and the pinger are Synchronised to measure the time difference between transmitting and receiving a pulse. A synchronising drift error which accumulates with time was corrected by using the time average of the distance which was calculated from the transmission loss. In this way we obtained more accurate measurement of distance. Using the distances calculated by the synchronising method, We fixed the ROV position using the range-range (p-p) positioning method. Compared with the hyperbolic positioning method, the positioning accuracy in this study is clearly improved.
