Accurate Ranging in a Stratified Underwater Medium with Multiple Iso-gradient Sound Speed Profile Layers

Most of the available localization algorithms require pair-wise ranging between the nodes. The more accurate the ranging, the more precise the localization. In this paper, the problem of accurate ranging between sensor nodes in an underwater environment is considered. It is assumed that the underwater medium is composed of layers with an isogradient depth-dependent sound speed profile (SSP). For the range estimation, we first show how the pair-wise time of flight (ToF) measurement between the nodes is related to the nodes’ positions. Then, based on this relation, we propose a novel ranging algorithm for an underwater acoustic sensor network (UASN). The proposed algorithm is based on the ToF measurement of the first arrival ray which may be reflected from the surface or the seabed. Through several simulations we show that the algorithm performs superb, and meets the Cramér Rao bound (CRB) for different values of the measurement noise power.