A Closed-form Estimator for Underwater Target Horizontal Position and Sound Speed Using Depth and TOA Measurements

This paper proposes a closed-form estimator that integrates depth and time of arrival (TOA) measurements to jointly estimate target horizontal position and sound speed. Firstly, the initial solution is obtained utilizing the null space projection (NSP) method. The estimation accuracy is then improved by error compensation. Furthermore, the Cramér-Rao Lower Bound (CRLB) is derived with hydrophone position errors. The simulation results demonstrate that the proposed method outperforms the two-step weighted least squares method (2WLS) and the NSP method without depth measurements (WNSP), and its performance can reach the CRLB.