The underwater acoustic localization of deep-sea UUV in the underwater acoustic sensor networks is mainly based on the geometric principle. Due to the uneven underwater sound speed, the propagation of sound ray is bent. It will produce great error to calculate the distance between the node and the UUV with constant sound speed. At the same time, the complexity of underwater environment makes it difficult to achieve accurate clock synchronization between the underwater node and the UUV, and the cost of maintaining clock synchronization is very high. Aiming at the clock asynchrony between the node and the UUV and sound ray bending, a clock-free synchronous localization method for deep-sea UUV based on sound ray correction with grazing angle and differential iteration was proposed. When the sound speed profile and the grazing angle of the node are known, the horizontal distance between the node and UUV can be obtained more accurately, and the UUV localization accuracy can be improved by differential iteration method. The performance is verified by Matlab simulation and simulation experiment with Bellhop. The results show that the traditional sound ray correction methods are no longer suitable for clock asynchronous situation between the node and the UUV, but the clock-free synchronous localization method for deep-sea UUV based on sound ray correction with grazing angle and differential iteration proposed in this paper can significantly improve the localization accuracy of UUV under the condition of grazing angle estimation error. In addition, the performance of the sound correction based grazing angle is simulated in the presence of grazing angle estimation error, which has practical guiding significance for the setting of node depth and the selection of nodes within the communication range.
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