Deep ocean long range underwater navigation

A long range Underwater Navigation Algorithm (UNA) is described that provides a geolocation underwater while submerged without having to surface for a Global Navigation Satellite System (GNSS) position. The UNA only uses measured acoustic travel times from a constellation of underwater acoustic sources analogous to the constellation of satellites in GNSS. The UNA positions are calculated without any a priori track, position or sound speed information, and thus provide a “Cold Start” capability. The algorithm was tested using data from the 2010–2011 Philippine Sea Experiment in which six sources were deployed in a pentagon ∼400 km on a side. 502 positions of hydrophones in a bottom-moored vertical line array at depths of 485–3037 m drifting in a tidal watch circle up to 600 m in diameter were computed. The sources were 129–450 km from the hydrophone receivers. The mean UNA position error from ground truth was 58 m with a standard deviation of 32 m. The UNA Cold Start Algorithm position can be used as the point in the ocean for calculating acoustic model runs from the source positions with a four-dimensional sound speed field from a general circulation model to improve the accuracy.