Magnetic Gradient Tensor Positioning Method Implemented on an Autonomous Underwater Vehicle Platform

Abstract

Underwater magnetic surveying serves as the fundamental prerequisite for detecting sensitive underwater targets and magnetically susceptible submerged objects. However, when utilizing magnetic gradient tensor measurements for underwater positioning, the stability of the measurement apparatus can be significantly affected by hydrodynamic disturbances in the underwater environment, thereby having a substantial impact on data quality. Autonomous Underwater Vehicles (AUV) are unmanned underwater robots designed to independently perform various tasks and operations in underwater environments. In order to ensure the quality of data collection, this paper proposes a structure utilizing an Autonomous Underwater Vehicles platform equipped with a three-component magnetic gradiometer. This structure employs second-order tensor positioning algorithms and vertical gradient positioning algorithms, coupled with the Autonomous Underwater Vehicles’s inherent vertical profile motion, to effectively achieve the precise positioning of underwater cables. Simulation results indicate that, in the absence of geomagnetic background noise, both horizontal and vertical structures yield favorable positioning results. However, when introducing background noise of 40,000 nT, the horizontal structure exhibits larger positioning errors, whereas the vertical structure demonstrates smaller errors. Experimental results show that in near-field scenarios, both structures achieve relatively similar positioning accuracy. Nevertheless, under identical distances in the far field, the vertical structure reduces errors by a minimum of 30.78% compared to the horizontal structure, thereby confirming the feasibility of integrating magnetic gradient tensor measurement structures with Autonomous Underwater Vehicles platforms.