Full Ocean Depth Unbiased Speed over Ground Estimation using a 3D Ultra Short Baseline Interferometric Doppler Velocity Sonar

A low bias Doppler Velocity Log (DVL) is important for underwater navigation performance, to limit the drift of inertial navigation. Existing DVLs achieve their low bias only by using very narrow pencil beams which, for practical transducer sizes, require very high frequencies of operation (e.g. 600kHz). This leads to very limited range to bottom (e.g. 100-150m).This paper presents a new long range DVL design comprising of a transmitter of diameter D steered towards the seabed and a 3D ultra-short baseline receiver array, of small dimensions compared to D. By cross-correlating the four received signals, a 4x4 Doppler phase matrix is computed, which allows the joint estimation of the Doppler phase and the mean wavenumber vector k. Thus the new DVL does not require an estimate of the sound velocity. By steering the transmitter in three or more independent directions in space, the velocity vector can be estimated. The performance of the new design is illustrated by simulations, which show the theoretical feasibility of a DVL with 6000m range and bias error below 0.1%.