A Vector Magnetometer System for Detection, Tracking, and Survey of Submerged and Buried Transmission Cables and Lines from Controlled Submersible Vehicle

A vector magnetic gradiometer array has been developed for the purpose of detecting, tracking, and surveying undersea, sub-bottom transmission cables and lines. The system is designed to be carried by the SCARAB vehicle or similar controlled submersibles. The basic sensor unit in the array consists of a combination of a 3-axis fluxgate vector component magnetometer and a single axis gradiometer utilizing a pair of aligned fluxgate sensors. Theoretical models of the magnetic fields of extended (linear) cables and lines are presented. These models are compared with empirical data obtained from magnetometer measurements in the vicinity of real cables having intrinsic ferromagnetic materials of high permeability and carrying electric currents. Data outputs for various sensor array geometries are compared, and criteria for optimum sensitivity of detection, tracking, and survey are discussed. Results of field tests of the system are presented and evaluated. The applications of the system for A.C. tone detection are also considered.