Underwater acoustic positioning system based on propagation loss and sensor network

Nowadays, the need for underwater robots to be used for research in the fields of ocean has becomes ever greater. For autonomous underwater robots, an accurate positioning system is very important in order to develop their full potential. Many positioning systems in water have being advanced dramatically and used in some areas. These systems almost based on time difference and phase lag, so they must to use atomic clocks and transponders. However, systems become very expensive and complex. And how to measure position in real time and expand the working area of the robot is another important research task to be waited to solve. In this study, we propose a new underwater acoustic positioning system use a new principle what is different from conventional systems. This system consists of distance measurement unit, sensor network unit, GPS unit and communication unit. In this study, we will explain the front two units. In the distance measurement unit, the distance can be calculated by using relation between sound propagation loss and propagation distance instead of basing on time difference or phase log. This method is simple for process, and can be measure longer distance winder areas. In sensor network unit, we set up each distance measurement unit as a standard station, use such three or more stations to construct network. The position of each station has already known when we set up. Using these data and distances from robot to each standard station, we can calculate the relative position of robot. In this system, we can increase sensor to expand the measurement area, therefore the problem of the sensor measurement limit can be solved. As the next tasks, we will introduce GPS unit into each standard station. Therefore, the absolute position of each station can be calculated correctly at any time whatever it is moving or still. And the absolute position of robot can be calculated by using these data. We will also introduce wireless communication system for sending d- ta to the control station, so all the measurement can be executed at the same time. We can expect that the real time positioning system can be established.