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Underwater localization is of great importance for marine observation andbuilding positioning, navigation, timing (PNT) systems that could be widelyapplied in disaster warning, underwater rescues and resources exploration. Theuneven distribution of underwater sound velocity poses great challenge forprecise underwater positioning. The current soundline correction positioningmethod mainly aims at scenarios with known target depth. However, for nodesthat are non-cooperative nodes or lack of depth information, soundline trackingstrategies cannot work well due to nonunique positional solutions. To tacklethis issue, we propose an iterative ray tracing 3D underwater localization(IRTUL) method for stratification compensation. To demonstrate the feasibilityof fast stratification compensation, we first derive the signal path as afunction of glancing angle, and then prove that the signal propagation time andhorizontal propagation distance are monotonic functions of the initial grazingangle, so that fast ray tracing can be achieved. Then, we propose an soundvelocity profile (SVP) simplification method, which reduces the computationalcost of ray tracing. Experimental results show that the IRTUL has the mostsignificant distance correction in the depth direction, and the averageaccuracy of IRTUL has been improved by about 3 meters compared to localizationmodel with constant sound velocity. Also, the simplified SVP can significantlyimprove real-time performance with average accuracy loss less than 0.2 m whenused for positioning.

Fast Ray-Tracing-Based Precise Underwater Acoustic Localization without Prior Acknowledgment of Target Depth