Precision 3D Underwater Electric Field Measurement Method for Accurate Marine Localization

This paper proposes a method to calibrate the axis misalignment of underwater electric field sensors (EFSs) for the accurate measurement of electric field signals induced by underwater objects and for the precise localization of the objects. We devised a mechanical system that calibrates an EFS to measure the 3-D components of the electric field signals and three-dimensionally localize the underwater objects with the measurements. To calibrate the EFS, it was installed underwater wherein a reference electric field was configured, and the electric field signals were measured. The misalignment among the axes of the EFS was approximated by comparing the electric field measurements and theoretical calculations under similar measurement conditions. The electric field measurements were then calibrated to the signals to be measured with an ideally structured EFS without axis misalignment. The proposed system was tested through computer simulations and water-tank experiments. The results indicate that the proposed system can estimate the axial misalignment of the EFS and calibrate its electric field measurements. Furthermore, to test the effectiveness of the proposed calibration of the EFS, electric-field-based localization of an underwater electric source was conducted; the distance errors between the actual and localized positions of the moving electric source were reduced after calibration of the EFS. The proposed system will contribute to missions such as underwater exploration, construction, and surveillance, which require accurate 3-D localization of underwater objects.