| Airborne full tensor magnetic gradient measurement technology,as an important means in the field of geophysical exploration,is widely used because of its strong practicability,wide application and rich magnetic anomaly information.DC superconducting quantum interference device（DC-SQUID）is also widely used as a sensor for magnetic measurement systems due to its advantage of high magnetic sensitivity.The full tensor magnetic gradient measurement system based on DC-SQUID sensor has been deeply studied in Australia,Germany,the United States and other countries,and has been gradually applied to geophysical exploration,military anti-submarine,unexploded ordnance detection and other fields.The purpose of this paper is to carry out the research of airborne high temperature superconducting full tensor magnetic gradient sensing system with field dynamic flight experiment ability,so as to form a set of feasible technical scheme.The research of this paper is funded by the"13th Five-Year Plan"national key research and development project"Aeromagnetic Field Measurement Technology System Development".The main research contents and conclusions are as follows:（1）Development of the prototype of airborne high temperature superconducting full tensor magnetic gradient sensing system.Aiming at the problem of low magnetic gradient sensitivity caused by short baseline of integrated DC-SQUID gradiometer,a method of constructing long baseline DC-SQUID gradiometer based on spatial difference principle of DC-SQUID magnetometer is proposed.By analyzing the theory of full tensor magnetic gradient measurement,a full tensor magnetic gradient measurement model based on 8 DC-SQUID magnetometers is constructed.The relationship between the uncertainty or sensitivity of magnetic gradient measurement and the baseline distance between DC-SQUID magnetometers is analyzed.Based on the designed full-tensor magnetic gradient measurement model,the first set of domestic high temperature superconducting full tensor magnetic gradient sensing system prototype with field flight measurement capability was developed.The magnetic gradient sensitivity noise level of each gradiometer is better than12.02p T/（m（?）Hz）@1k Hz.（2）Research on the suppression method of losing lock of airborne full-tensor magnetic gradient sensing system.Aiming at the problem of losing lock caused by insufficient dynamic range of sensor system under field dynamic measurement conditions,a method of expanding the dynamic range of sensor system based on feedback compensation technology is proposed,which solves the problem of losing lock caused by insufficient dynamic range.Based on the attitude data obtained from the verification flight experiment of the helicopter mounted non-magnetic pod,the dynamic range requirement of the sensing system is analyzed and calculated.Based on the principle of expanding the dynamic range by feedback compensation technology,the feedback compensation hardware circuit and program are designed.The electromagnetic shielding room verification experiment proves that the proposed method improves the dynamic range of the sensing system by 18.98 d B on the original basis.Aiming at the problem of losing lock caused by radio frequency interference,through the analysis and calculation of the electromagnetic wave absorption loss and reflection loss process,the suppression of radio frequency interference based on electromagnetic shielding technology is realized,thus solving the problem of losing lock caused by radio frequency interference.The field dynamic measurement experiment carried out by the self-made non-magnetic car equipped with the sensing system confirms the effectiveness of the proposed method.（3）Research on the crosstalk error calibration method between DC-SQUID magnetometers in sensing system.Aiming at the problem of crosstalk error between DC-SQUID magnetometers in full tensor magnetic gradient probe,a crosstalk error calibration method based on triaxial Helmholtz coil is proposed.Based on the analysis of the working principle of zero flux locking readout circuit of DC-SQUID magnetometer,the cause of crosstalk error between DC-SQUID magnetometers is clarified.The crosstalk error model and objective function between 8-channel DC-SQUID magnetometers in full tensor magnetic gradient sensing system are established.Through differential operation and formula derivation,the crosstalk error calibration problem is transformed into the problem of constructing a column full rank matrix with linear independent column vectors.Finally,a crosstalk error calibration method between DC-SQUID magnetometers based on triaxial Helmholtz coil is proposed.Repeated simulation results confirm the effectiveness of the method.Through the electromagnetic shielding room experiment,56 crosstalk error coefficients between 8DC-SQUID magnetometers are obtained.The experimental results show that the crosstalk error coefficient between DC-SQUID magnetometers with the most serious crosstalk in the sensing system reaches 0.02452.The proposed crosstalk error calibration method avoids the crosstalk error of 85.82 n T between DC-SQUID magnetometers in extreme cases.（4）Research on imbalance calibration method of airborne full tensor magnetic gradient sensing system.Aiming at the problem of gradient imbalance in the gradiometer composed of DC-SQUID magnetometer by spatial difference in the sensing system,an imbalance vector calibration method based on coordinate transformation theory is proposed.All the error parameters that cause the gradient imbalance are obtained by using the triaxial Helmholtz coil while keeping the probe stationary,thus avoiding the motion noise interference caused by the traditional method due to the need of rotating the probe during the calibration process.The field comparison experiment proves the superiority of the coordinate transformation method over the traditional probe rotation method.Aiming at the problem that both the coordinate transformation method and the traditional method are sensitive to the fluctuation of the background magnetic field,an imbalance scalar calibration method based on the full-space rotating magnetic field theory is further proposed.The triaxial Helmholtz coil is used to generate a magnetic field that can rotate in full space,the magnetic field intensity is constant and the frequency is controllable.Finally,the ellipsoid fitting theory is used to solve the error parameters,which not only avoids the motion noise caused by the probe rotation in the calibration process,but also reduces the influence of the background magnetic field fluctuation on the imbalance calibration process by increasing the frequency of the rotating magnetic field.Experiments show that this method improves the imbalance index of all gradiometers in the sensing system to better than1.1×10-5,ensuring the accuracy of each magnetic gradient component measurement result.（5）Performance parameter test and field flight experiment of full tensor magnetic gradient sensing system.In order to determine the performance parameters of the prototype of the developed sensing system,the performance parameter test experiment is carried out.By studying the test method,the key performance parameters such as the magnetic gradient sensitivity noise level,the magnetic field intensity detection sensitivity and the measurement range,bandwidth,and slew rate of the sensing system are tested.The factors affecting the key performance parameters of the sensing system are summarized through the test results.On this basis,the dynamic flight measurement experiment of the sensing system under the condition of field helicopter mounting is carried out.Through the design of the flight line,the regional area of the airborne full tensor magnetic gradient measurement experiment is carried out.The experimental results show that the prototype of the airborne full tensor magnetic gradient sensing system developed in this paper has the ability of field measurement to a certain extent,which lays a foundation for the independent design and development of domestic and practical airborne high temperature superconducting full tensor magnetic gradient instrument equipment. |
PDF Full Text Request