US 10955523 B1 / Mar 23, 2021

Deep ocean long range underwater navigation algorithm (UNA) for determining the geographic position of underwater vehicles

An underwater navigation algorithm (UNA) uses acoustic signals transmitted in the ocean from sources at known positions to compute a position underwater for a vehicle that requires no initial a priori position or any ocean sound speed information or any initial GPS position that would require surfacing. The UNA consists of two parts, (1) the Cold Start Algorithm (CSA) and (2) the CSA with Modeling (CSAM). The underwater vehicle needs to be equipped with only a single hydrophone acoustic receiver and an onboard processor. The CSA requires only measuring the travel time of the end of the arrival coda (EOC) from each of the sources to compute a position. The CSAM is a post CSA procedure to calculate a higher accuracy position using the CSA position. CSAM utilizes the CSA position and a 4D sound speed field derived from an ocean 4D General Circulation Model (GCM) constrained using Ocean Acoustic Tomography (OAT) in the ocean area of operation and further includes (1) computing a modeled result with an acoustic propagation modeling code that is compared with the received acoustic data using a known procedure called “bulk shifting” and/or (2) a new proposed procedure that uses calculated group speeds from the 4D sound speed field, to provide a higher accuracy estimate of the receiver position.