Robust hybrid visual servoing for hovering control of autonomous underwater vehicles in unstructured environments

This paper presents a novel hovering control method for autonomous underwater vehicles (AUVs) based on a hybrid visual servoing (HVS) framework, designed to achieve accurate and stable pose regulation of AUVs relative to static targets in unstructured underwater environments. The proposed method, which integrates a robust $H_{\infty }$ controller within a dual-loop control architecture, effectively addresses underwater image degradation, parameter uncertainties, and external disturbances encountered in unstructured environments. In the outer loop, visual features derived from image moments of underwater targets are utilized to design a position control law, enhancing robustness against underwater image degradation. In the inner loop, a robust $H_{\infty }$ controller is designed to accurately track the velocity commands generated by the outer loop, providing robustness against hydrodynamic coefficient perturbations and external disturbances. The performance of the proposed hovering control method is validated through extensive comparative simulations and experiments using an AUV prototype. Results demonstrate that the method enables accurate and stable hovering control of the AUV, supporting autonomous close-range observation of underwater targets in unstructured environments.