Abstract
When using the technique of magnetic gradient tensor measurements to obtain the position of magnetic objects, calibration of the magnetic tensor gradiometer plays a pivotal role in precisely locating the target, and extensive research has been carried out on this up to now. However, previous studies have always lacked sufficient discussion on the position error of magnetometers in magnetic tensor gradiometers caused by inaccurate installment of magnetometers. In this paper, we analyze and correct this position error based on a magnetic dipole source. The result of the simulation exemplifies that the magnetometer’s position error will affect the locating accuracy and, therefore, it is worth correcting this error. The relationship between position error and magnetic gradient tensor components is established, followed by an error correction method based on this relationship. Simulations illustrate that this method can effectively decrease the effect caused by the position error of magnetometers and improve the locating performance with locating error and magnetic moment errors dropping from 2 to 0.2 m and to , respectively.
Highlights
The magnetic gradient tensor system has been extensively applied in geophysical exploration [1], such as underwater target detection and unexploded ordnance [2], due to the advantages of magnetic gradient tensor measurements, the unstoppable development of technology, and the improvement in various platforms [3]
An inherent error exists in the magnetic gradient tensor system in obtaining the magnetic gradient tensor components, as the magnetic gradient tensor is generally approximated by the numerical difference between two separated magnetometers instead of the differential
Rong et al used the hybrid model of an ellipsoid and magnetic dipole array to simulate and analyze the measurement performance of several typical magnetic gradient tensor systems with different geometric configurations, and proposed that the cross-shaped magnetic gradient tensor system has the characteristics of an optimal structure with minimum measurement error [6]
Summary
The magnetic gradient tensor system has been extensively applied in geophysical exploration [1], such as underwater target detection and unexploded ordnance [2], due to the advantages of magnetic gradient tensor measurements, the unstoppable development of technology, and the improvement in various platforms [3]. Chi et al obtained the calibration matrix [15] by solving the orthogonal Procrustes problem; Qingzhu et al proposed that calibration of misalignment errors can be completed just by three sets of measurement data with the same rotation period [16] All these methods only consider the misalignment error when installing the sensor, but do not consider the position error of magnetometers caused by inaccurate installment. The position of the sensor’s center may not accurately be at its geometric center, or magnetometers may not be correctly installed at the required position, especially for the magnetic gradient tensor system with flexible baseline length in which magnetometers will be slightly inaccurately installed along its axis after each change in baseline This error will lead to a difference between the actual baseline length and standard baseline length of the tensor system, which significantly affects the accuracy of the obtained magnetic gradient tensor and locating results. The simulation results of the above content are clearly shown
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