Correction of a Towed Airborne Fluxgate Magnetic Tensor Gradiometer

The small impact of the geomagnetic field enables a magnetic tensor gradiometer to be easily installed on the flight platform for airborne geophysical exploration, especially for the detection of shallow buried mines and magnetic moving targets. Using the fluxgates as the core components, the gradiometer has the advantages of wide temperature range, low cost, and high resolution, but has the disadvantage of relatively low accuracy. This is because of the scale factor error, the nonorthogonal error, the misalignment, the zero offset, the dynamic error in a fluxgate, and the inconsistency among the error of fluxgates. In this letter, a correction method for a towed airborne magnetic tensor gradiometer is proposed that is composed of four fluxgates arranged in a cross-shaped structure. The theoretical framework of the proposed method is based on the static error model and the dynamic characteristics of single fluxgate, the feature that the gradient tensor of the geomagnetic field at high altitude is approximately zero, and on the phenomenon that the unchanged tensor rotation as a result of nonuniform magnetic field on the ground can indicate the inconsistency of the scale factors among different tensor components. The actual flight results using a helicopter have demonstrated and validated the performance and effectiveness of the proposed method. The improvement ratios of the field tensor components are from 359.6 to 1765, and the RMS of each component has reached to the level of 1 nT/m.