In order to obtain the plane magnetic field data at different heights above a ship and solve the problem of calculating the plane magnetic field from the vaulted magnetic field above the ship, this paper proposes a method for calculating the magnetic field above the ship using the equivalent surface magnetic charge.

Based on the theory of equivalent source, the magnetic field data of the vault is used for inversion modeling. As the ship's magnetic field is equivalent to that generated by the surface magnetic charge, it is calculated accordingly to simulate the magnetic field above the ship. The magnetic field calculated by the surface magnetic charge method is then compared with the ship's actual magnetic field to verify the feasibility of the surface magnetic charge method.

Through numerical simulation, the relative root mean square error of the vertical component of the ship's magnetic field calculation is 0.44%. Using the magnetic field ship model, the relative root mean square error of the vertical component calculation is 7.64%.

The simulation and ship model experiment analysis herein show that the calculated value of the magnetic field using the surface magnetic charge method is consistent with the measured value. Moreover, the relative root mean square error of the calculated value is small and has high precision, which makes it feasible for use in practical engineering calculation.