Research On Observation Technology Of Buried Fluxgate Magnetometer

The geomagnetic field is one of the fundamental and most important physical fields of the Earth,and its changes contain rich information about the dynamics of the Earth’s interior and the geospace environment.The National Geomagnetic Network provides data on the geomagnetic field and its dynamic evolution for earthquake monitoring and prediction,as well as for applications such as Earth science research and National defence construction.At present,the distance and number of existing stations are far from providing the spatial resolution required for research and applications,and because of the blank monitoring areas,it is not fine enough to monitor of the dynamic background of the changing magnetic field across the country,therefore,it cannot effectively support the seismic and geomagnetic anomaly information,such as anomalous daily geomagnetic changes.To extract this information effectively,it is necessary to increase the observation density of geomagnetic stations and improve the observation capabilities of the geomagnetic station network.However,due to high requirements on the surrounding electromagnetic environment,large footprint,high construction costs and so on,ground geomagnetic stations have faced great difficulties in site selection and station construction.With the rapid development of China’s economy,urban expansion,highway,high-speed rail,subway and other transportation and other infrastructure construction,as well as peoples’s modern production and lifestyles,the living space of existing stations has also been compressed and geomagnetic observation data has been affected and degraded seriously.In recent years,the buried and underground observations with less land occupation,low cost,and good resistance to ground interference are considered to be one of the development directions of the next-generation geomagnetic observation technology.Therefore,it is of great practical significance to carry out the research on the observation technology of the buried fluxgate magnetometer.In this paper,based on the analysis of the research status of the buried magnetic measurement method and the three-component magnetic sensor at home and abroad,according to the requirements of the geomagnetic field measurement environment,the key technology of fluxgate magnetometer with large measuring range and convenient for buried installation and observation was studied,the data management host of the fluxgate magnetometer for buried geomagnetic observation was developed,and the orientation error correction research was carried out for the buried fluxgate magnetometer.The main research content of this paper is as follows:(1)Research on key technology of large dynamic range fluxgate magnetometer adapted to underground installationThe fluxgate magnetometers with a dynamic range of ±2500nT in ground stations often used in relative observation method,and the main background magnetic field needs to be compensated.In order to meet the needs of underground geomagnetic observation and fluxgate magnetometer attitude self-calibration,this paper designs a fluxgate magnetometer signal detection and processing circuit with a large dynamic measurement range,small zero point error,low noise and a data acquisition system with multi-channel and high performance.Laboratory test results show that the three-component fluxgate magnetometer in this peper has a noise of less than 0.02nT@1SPS and a linearity of better than 6‰ when the dynamic range of the H and Z components is not less than±65000nT and the dynamic range of the D component is not less than±2500nT,the absolute value of the zero deviation of the D component is less than 2.5nT and the frequency band range is DC0.4HZ.(2)Development of data management host for fluxgate magnetometerIn order to adapt to the harsh environment of field observation,a fluxgate magnetometer data management host has been developed using ARM+Linux embedded computer technology to meet the requirements of stable operation and low power consumption.Using the RS422 bus and buried sensor for data transmission,the communication requirements of long-distance anti-interference and high reliability were realised.The high-precision GNSS timing function of the collected data was realised by the real-time transmission of the sensor module acquisition and the host hardware interrupt response to the PPS second pulse.In addition,RJ45 network communication,local largecapacity data storage in SD card and other functions.of the data management host have also been realized.(3)Research on correction method of orientation error of fluxgate mmagnetometer suitable for underground installationIt is difficult to accurately orient the instrument in a narrow space when it is buried underground.In order to obtain the orientation error angle of the observation instrument and perform selfcalibration measurement without reference instruments,this paper proposes a method based on large dynamic range fluxgate magnetometer and data correction method for Euler rotation transformation.Through the fluxgate three-component geomagnetic observation data,the orientation error angle of the fluxgate magnetometer was obtained and the data orientation correction was performed.Through the experimental verification at the geomagnetic observation station,the results show that even if the orientation error was set to a large angle in four different quadrants,the correlation coefficient with the corresponding component of the station comparison instrument can still reach more than 0.99 after the correction,as shown in Figure B-A.The length of the central confidence interval is reduced by more than 86%,and the RMS error is reduced to less than 15%.