An Experimental Consideration on Accuracy of Inverse Super Short Baseline Underwater Positioning Using Acoustic Data Transmission

Abstract

Authors are developing a test system of new type acoustic positioning system (APS) using inverse super short baseline (ISSBL) method. In this method, the vehicle is equipped with hydrophone array. Direction of arrival (DOA) of acoustic signal from mother ship is detected, and relative position between the mother ship and the vehicle is calculated with the measured DOA and the depth. Information of ship’s position is included in the transmitted acoustic signal, then absolute position of the vehicle can be calculated with the relative position and the included information. The vehicle position can be obtained in the vehicle in real-time and be used directly to navigate. No reply from the vehicle is necessary. Five ocean experiments were conducted in various depth points. In the experiments, an experimental device was moored at sea bottom, and the ship cruised around above the moored device with transmitting acoustic signal including the ship’s information. In consideration about random scattering of positioning result, followings were found. Random scattering is much suppressed with EKF using high rate symbol value. On the other hand, estimation error of ship’s position, which is about 0.5–1 meter, is not negligible. When the DOA measurement for each symbol is accurate, the estimation error of the ship’s position becomes dominant in output of EKF as a consequence of random scattering suppression. Therefore, this method is more advantageous in case the DOA measurement have larger random error. Then this method is useful in deeper case and small array can be adopted to the system. On the other hand, this method do not perform well when the elevation angle from the target to the ship is shallow. Moreover convergence percentage seems to touch the lowest value at around 10%.