Study and implementation of an EKF GIB-based underwater positioning system

The paper addresses the problem of estimating the position of an underwater target in real time. In the scenario adopted, the target carries a pinger that emits acoustic signals periodically, as determined by a very high precision clock that is synchronized with GPS, prior to system deployment. The target is tracked from the surface by using a system of four buoys equipped with hydrophones and electronic circuitry that measures the times of arrival of the acoustic signals emitted by the pinger or, equivalently, the four target-to-buoy range measurements (a commercial version of this setup is the GIB system). Due to the finite speed of propagation of sound in water, these measurements are obtained with different latencies. The paper tackles the problem of underwater target tracking in the framework of extended Kalman filtering by relying on a purely kinematic model of the target. The paper further shows also how the differently delayed measurements can be merged using a back and forward fusion approach. A measurement validation procedure is introduced to deal with dropouts and outliers. Simulation as well as experimental results illustrate the performance of the filter proposed.