Development Of Data Acquisition And Recording System For Airborne High-temperature SQUID-based Full Tensor Magnetic Gradiometer

As an important method in the field of geophysical exploration,aerial magnetic exploration technology not only gets rid of the constraints of terrain conditions to a certain extent,but also greatly improves the detection efficiency.Compared with the traditional total magnetic field measurement and three-components measurement,the magnetic gradient tensor measurement has the advantages of highlighting the abnormal field,weakening the background field,insensitive to attitude changes,and more accurate inversion results.Thus,the magnetic gradient tensor measurement based on the aerial mobile platform is of great research value.We developed a data acquisition and recording system for airborne high-temperature SQUID-based full tensor magnetic gradiometer,which realized the synchronous acquisition of magnetic data recorded by eight-channel SQUID circuit and attitude data recorded by Inertial Navigation System(INS).The static experiment in the shielding room,the ground dynamic experiment in the field and the flight experiment in the field verify the stability and reliability of the system.This dissertation expound the principle of magnetic gradient tensor measurement,and derived 5 independent components of the 9 components of the magnetic gradient through theoretical derivation.That is,all tensor elements can be obtained by measuring these 5 independent components.The classification of SQUID magnetic sensors and the working mechanism of DC SQUID are introduced.According to the above measurement principle of the magnetic gradient tensor,the hardware platform of the data acquisition system is designed,including the multi-channel digital SQUID readout circuit and the NI c RIO data acquisition and instrument control module.The former is used to output the SQUID voltage signal after amplification and integration,and cooperate with the upper computer to complete the digital adjustment of SQUID status and parameters.The latter is mainly used to realize the synchronous acquisition of the eight-channel SQUID magnetic data and INS data,and provide corresponding serial communication interface for RS-485 communication between upper and lower computers.In order to realize the digital adjustment of the status and parameters of SQUID,we use the RS-485 serial communication function and write the upper computer control program and the lower computer main control program.Here,LabVIEW software was used to develop NI c RIO embedded platforms,including LabVIEW FPGA and LabVIEW Real-Time programming.The former realizes system functions by controlling the I/O module,while the latter processes,displays and stores the collected data in real time,and realizes the synchronization of eight-channel SQUID data and inertial navigation data by GPS synchronization.Aiming at the “unlock” of SQUID during flight measurement,we propose an unlock detection method of,that is,to determine the differential entropy of the SQUID output voltage signal,and then design a automatic recovery scheme of the SQUID operating point.Finally,the performance test and feasibility verification experiment of the data acquisition system for airborne high-temperature SQUID-based full tensor magnetic gradiometer were carried out.Test and experiment results show that the system meets the expected indicators,RS-485 serial communication,SQUID unlock detection and automatic recovery functions are realized,the noise level is less than 200?V,and the synchronization accuracy of SQUID magnetic measurement data and INS data is better than 10?s.By comparing and analyzing the results of flight experiments in the survey area,the authenticity and validity of the data collected by the system are verified,and the design requirements of the data acquisition and recording system for airborne high-temperature SQUID-based full tensor magnetic gradiometer are satisfied.