Research On Ground Three-component Magnetic Diurnal Variation Measuring Device Based On Fluxgate

As an important geophysical exploration method,aerial magnetic survey has the characteristics of high detection efficiency and strong adaptability to terrain.Compared with the traditional total field and its gradient measurement,aerial three-component magnetic survey can obtain more abundant magnetic field information,which is conducive to the qualitative analysis and quantitative interpretation of magnetic anomalies.However,the geomagnetic field changes with time and place,the influence of magnetic diurnal variation on the quality of the three-component magnetic measurement data cannot be ignored.Therefore,eliminating the influence of magnetic diurnal variation is an important step to improve the accuracy of the aerial magnetic measurement.The number of geomagnetic stations in China is small and the distribution is uneven.The measurement accuracy is low,if the magnetic diurnal variation information measured by the geomagnetic stations is used for aeromagnetic three-component compensation.In order to obtain high-precision geomagnetic diurnal variation information,a three-component magnetic daily variation measurement device on the ground is designed based on the fluxgate sensor and the method of measuring azimuth based on differential GPS.Firstly,this article introduces the origin of magnetic diurnal variation,the seven elements of the geomagnetic field and their mutual conversion relations.The principle of magnetic diurnal variation observation based on the fluxgate sensor is analyzed,and comes up with a method to search for geographic north to implement three-axis orientation of the fluxgate based on this principle by using differential GPS technology.Because the magnetic axis of the fluxgate and the optical axis of the telescope are not strictly parallel,there is an orientation deviation.The triaxial orientation method is optimized.The errors caused by the whole observation process were analyzed theoretically.The errors were reduced by means of forward-looking observation method and increasing the distance from the measuring point to the marker.According to the working principle and signal output characteristics of the fluxgate sensor,a low-noise signal acquisition module hardware circuit module is designed,including a signal conditioning circuit,an analog-to-digital conversion circuit,a main controller circuit,storage,display,and power supply.The development of main controller software and host computer software was carried out.The upper computer mainly includes LabVIEW debugging interface and GPS data processing program.After the development of the three-component magnetic diurnal variation measuring device,the test calibration and field experiments were performed.Perform short-circuit noise test on the AD acquisition card.After spectrum analysis,the signal-to-noise ratio is better than 120 dB,which can meet the detection index of the fluxgate sensor with a resolution of 0.1nT.A non-linear correction experiment of the fluxgate is designed,and the conversion coefficients of voltage and magnetic field are calibrated.The results are consistent with the data of the Spectramag-6 standard acquisition unit corrected by Bartington.The magnetic daily change measuring device was tested in the field as a whole.By comparing with the magnetic daily change data of the geomagnetic station,the two data are consistent,which proves that the developed magnetic daily change measuring device has practical application significance.