Research On Technology Of Geomagnetic Field Relative Recording

The geomagnetic field is the global geophysical fundamental field,and the objective of geomagnetic observation is to continuously monitor the changes of the geomagnetic field with high accuracy in a long-term time frame.The data collected from geomagnetic observation provide valuable resources,to study the changes in the electromagnetic properties of related current systems or media,and can be applied to multiple divisions of earth and space science research,earthquake prediction and social applications,et al.The geomagnetic field is characterized by large ranges in amplitude and long time scales.The absolute value of the geomagnetic field elements has been used to obtain an understanding to the long-term change of the geomagnetic field,and the continuous measurement of the variation of the geomagnetic field element has been used to understand the rapid and small-scale changes of the geomagnetic field.These two observation methods are traditionally referred to as geomagnetic absolute observation and relative recording.At present,the typical geomagnetic relative recording observation instruments have shown limitations in long-term stability,response speed,installation convenience et al.Higher requirements are emphasized on magnetic measuring instrument with the development of research fields such as positioning and navigation,magnetic exploration,magnetic anomaly target detection.In addition,the traditional geomagnetic observation patterns are changing with new principle,new material and new technology,which has been expanding the conventional geomagnetic observation to multi-mode methodologies.Focusing on the future development needs of the science research,earthquake monitoring and forecasting,and social applications,this paper summarizes the current status of ground geomagnetic observation and analyzes the limitations of the geomagnetic observation network relative recording.Suggestions are provided on the development trend of geomagnetic relative records and development direction of observation instruments.This research provides technical support for configuring the geomagnetic observation systems with advanced observation technology and high-quality measurement data.1.Developed a high-stability three-component magnetic sensor based on fluxgate effect.The core as magnetic sensitive element of developed fluxgate sensor is formed by alloy frame of high plasticity,endurance strength wrapped with high permeability permalloy strip and excitation coil,and fiber reinforced plastics frame wrapped with pick-up and compensation coil respectively,for suppressing the influence of outside temperature and obtaining low temperature coefficient of the sensor.In order to achieve low perming and reduce noise of fluxgate sensor,the amplitude and frequency of excitation current is analyzed from mathematical calculation as the key factor,and the ideal excitation waveform is obtained by using the excitation tuning method.The fluxgate sensor is fixed at the suspended platform in order to automatically maintain the horizontal level,since the tilt of the instrument pier is normally the main cause of baseline drift and level error can be produced during the installation process.A special gimbaled construction is used which allows its auto-leveling to the vertical position of Z axis within tilts ±6degrees of arc.The performance of the proposed sensor has been tested in a zero-magnetic device and the results show: the linearity< 1 ‰,the noise < 0.04nT(RMS).So far,the developed instrument has been in operation for more than three months continuously in Shexian geomagnetic station,The monthly residual standard deviation maximum value of D,H,Z,component are 0.08',0.93 nT,0.69 nT respectively,which are smaller than the requirements of China's geomagnetic network,so the observation data and baseline values indicate that the prototype is stable and reliable.It is proposed to achieve long period geomagnetic field monitoring with high resolution,low noise and long-term stability relative recording instruments.2.Developed a new vector magnetometer based on OVERHAUSER effect sensor.Firstly,a brief description of the measurement principle and a review of formulae used for inclination,declination and total field component calculations are given,based on which the orientation of the magnetic axis of a set of orthogonal bias coils and relationship of measurement data during a measurement cycle are determined and analyzed.The noise level of prototype,which affected by the homogeneity of spherical coils and the amplitude of the bias magnetic field,are estimated and discussed.In order to verify the theoretical analysis,the prototype isset up on geomagnetic observatory to test the performances.The results show that non-homogeneity of spherical coils improves the performance by 5‰,and the optimal noise elimination performance can be achieved under the amplitude of the bias magnetic field about 20% of total field,and the noise of total intensity F,magnetic declination D and magnetic inclination I is 0.11 nT,0.032',0.014',respectively,which could be applied to the geomagnetic station with high sampling rate,multi-component quasi-absolute performances.3.Developed a weak magnetic sensor based on fundamental-mode orthogonal fluxgate effect using an amorphous wire.The core material is Co-based amorphous wire with cold-drawn and annealed using a vacuum melt drawing device.Firstly,we optimized the working point of the magnetic core material and determined the amplitude and frequency of the excitation field.The low-noise signal pick-up circuit has been designed,and the prototype performance test and the station comparison observation experiment has been proposed.The results show that the noise < 0.2nT(RMS),the frequency band response DC ~ 30 Hz,the sensor volume?7cm×10cm and power consumption< 1W,the prototype is portable and suitable for short-term earthquake tracking and monitoring intensively of magnetic anomaly areas.4.Developed a calibration method of geomagnetic field data.According to the geomagnetic daily variation records of National geomagnetic observatory network,we analyzed the observation data inconsistency from multiple sets of tri-axial fluxgate sensors in the same observation environment.Through theoretical calculations and experimental tests on the geomagnetic station,quantitative relationships has been investigated between instrument horizontal and orientation with each geomagnetic component.Based on the differentiation algorithm,the consistency of the measurement data of the geomagnetic station has been analyzed and corrected.The single and multiple observatory data corrections are implemented using the related software,which promises to provide high-quality observation data for scientific research.