Research and Field Test of Autonomous Underwater Vehicles Cooperative‐Navigation Method in Terrain Mapping

ABSTRACT A cooperative‐navigation algorithm based on an extended Kalman filter (EKF) is proposed for Leader–Follower autonomous underwater vehicles (AUVs) to address inconsistencies in inter‐vehicle navigation coordinate systems caused by the absence of geo‐referencing signals in anchor‐free environments. The algorithm integrates inertial compensation and a dynamic ranging threshold to address challenges posed by low update rates (0.05–0.07 Hz), high latency, time‐varying hydroacoustic channels, and multipath interference in hydroacoustic communication, all of which significantly degrade navigation accuracy. To mitigate latency from low‐rate hydroacoustic links, we use time‐tag alignment (UTC‐referenced clock synchronization) to propagate the Leader state to the effective ranging time for inertial latency compensation. In response to the hydroacoustic channel variability and multipath interference, a dynamic ranging threshold based on the AUV's motion capabilities is proposed to eliminate outlier ranging data. To enhance the robustness of cooperative navigation and maintain a coordinate system, a velocity‐bounded constraint is introduced into the EKF framework, limiting the magnitude of individual position corrections. During a field test at Danjiangkou Reservoir, Henan Province, China, AUVs cooperatively mapped an underwater terrain area of at a water depth of 45–55 m. Compared with terrain mapping using a single‐AUV inertial navigation system, the proposed cooperative‐navigation method improved the agreement of the terrain mapping with a Global Navigation Satellite System (GNSS)‐aided surface reference map by 15.89% relative to the inertial navigation baseline, which supports the effectiveness of the proposed cooperative‐navigation method during the mapping mission. Furthermore, the root mean square error (RMSE) of distance measurements between Leader AUV and Follower AUVs during linear transects decreased by 59.13% and 55.21%, respectively, indicating improved Leader–Follower range consistency achieved by the proposed method. In a Weihai open‐sea campaign with a desired Leader–Follower separation of 100 m on straight‐line segments, the resulting separation RMSE was 6.29 and 4.41 m for the two Followers, respectively. Moreover, in a Danjiangkou surface test with continuous GNSS ground truth (GNSS used only as an external reference, not as filter inputs, except for mission‐start initialization where applicable), the Followers' horizontal RMSE decreased from 15.09 m/13.00 m (INS) to 9.38 m/8.71 m (cooperative).