Modelling and analysis of depth-averaged currents for underwater gliders

Depth-averaged currents (DACs) represent the influence of ocean currents on a single profile of underwater gliders (UGs) and play a crucial role in path following and path planning. However, the motion characteristics of UGs are often overlooked in DAC calculations and applications. This study integrates the motion characteristics of UGs to perform modeling and analyze DACs. Case study results indicate that the DAC is not a static parameter even when the current is static, which fluctuates with the profile navigation commands. The Monte Carlo simulation method is employed to analyze the sensitivity of DAC to profile navigation command parameters and its response range, and a surrogate model is utilized to enhance computational efficiency. The simulation results indicate that the DAC magnitude can vary by up to 0.12m/s, with the directional shift reaching as much as 45 degrees. A hierarchical weighting is proposed for calculating ocean model-derived DACs to aid engineering applications. Sea trial data demonstrate that the DAC field can be affected by profile navigation commands. The DAC obtained by the hierarchical weighting shows good agreement with that obtained by dead-reckoning projection, offering a 5% improvement in accuracy. This research provides a valuable reference for the path planning of UG.