| Wide field electromagnetic method is a new controlled source frequency-domain electromagnetic method developed in recent years.It has the characteristics of large exploration depth,high detection accuracy and strong anti-interference ability.It is widely applied in many exploration fields such as metal minerals,oil and gas resources,and geothermal energy.However,with the further exploration demand,especially facing the complex terrain conditions,urban engineering environment and other application scenarios,its technical means and instruments have been limited greatly.To expand the application field of the wide field electromagnetic method,the ground-airborne wide field electromagnetic method is proposed,which has the advantages of high-power multi-frequency pseudo-random signal transmission on the ground and efficient continuous acquisition of air-borne electromagnetic signals.This paper mainly carries out innovative research work on the method theory,instrument equipment,signal acquisition,data processing,system integration and other aspects of the ground-airborne wide field electromagnetic receiving system:1.A scheme of a wide field electromagnetic aerial observation system based on the Hy component of the magnetic field is established.Based on Maxwell’s equations,this paper deduces the exact expression of the threecomponent magnetic field of ground transmitting-aerial receiving.Through the forward calculation of the typical model and the analysis of the response characteristics,it is verified and concluded that the magnetic field horizontal component Hy has the characteristics of large signal amplitude,wide observation range,and little influence by the sensor attitude and flight height.Considering the influence factors such as observation area,signal strength,attitude parameters,and sensitivity of underground medium,a scheme of a wide field electromagnetic aerial observation system based on the Hy component of magnetic field is proposed,which lays a theoretical foundation for the development and integration of the system.2.A multi parameters inductive coil suitable for the aerial weak magnetic field signals acquisition is developed.The LCR equivalent circuit model of the coil is established.The core parameters of the coil are designed by analyzing the influencing factors of the resonant frequency.The low noise level of the coil is accomplished through the design of low-noise operational amplifier circuit and high-order filter circuit.The structure and winding method make the coil both lightweight and good frequency response.The multi-parameter acquisition of magnetic field signal,attitude data and position information is accomplished through the integration of the attitude measurement module and GPS positioning module.A magnetic field signal acquisition sensor with reasonable sensitivity(50m V/n T)and bandwidth(40Hz～20k Hz)is provided for the ground-airborne wide field electromagnetic receiving system.3.A ground-airborne wide field electromagnetic receiver with low delay,ultra-low noise,and lightweight characteristics is developed.Through the signal reconstruction method combined with the synchronization scheme of GPS to tame the constant temperature crystal,the low-delay synchronous sampling of the signal is accomplished.The digital signal processing technology and the ultra-low noise analog circuit design technology are applied to reduce the scale and noise of the analog circuit.The ultra-low noise signal acquisition is accomplished.Based on the multi-core synergy mechanism of the high-performance STM32MP1 platform,the high real-time performance core M4 exchanging data with the CPLD,and the dual-core A7 with strong processing capability with the efficient operation of the Linux system,high-fidelity acquisition of signals and real-time storage and fast calculation of data are accomplished.The miniaturization of receivers is accomplished by using reduced analog circuit design and integrated digital processing system.Remote control and status monitoring of receivers is accomplished by using Lo Ra wireless communication scheme.The multidimensional processing and analysis of signals is accomplished by developing a signal analysis software including a variety of data processing functions.A signal acquisition platform with low delay,ultra-low noise,and light weight(the weight of the whole machine is 0.9kg)is provided for the groundairborne wide field electromagnetic receiving system.4.Based on the aerial Hy component observation scheme,the integration and verification test of the ground-airborne wide field electromagnetic receiving system has been completed.Based on factors such as the groundairborne wide field electromagnetic observation scheme,the connection of the carrying platform,the coil structure,the electromagnetic interference,and the flight strategy,the system noise was classified and analyzed,and a suspension system that effectively suppressed noise was designed.The ground-airborne wide field electromagnetic system is integrated with the receiver,multiinductive coil,UAV carrying platform and ground acquisition control station.The comprehensive performance test of the system was carried out in Jinan,Shandong and Baotou,Inner Mongolia,to verify the overall stability and effectiveness of the system,which is capable achieve effective acquisition of ground-airborne electromagnetic signals.Based on the above research work,this paper establishes a wide field electromagnetic aerial observation system scheme based on the Hy component of the magnetic field.A ground-airborne wide field electromagnetic receiving system based on a multi-rotor UAV has been developed.The field test has verified the comprehensive performance of the system,which can meet the requirements of effective acquisition of groundairborne electromagnetic signals.This paper has formed the key technology of ground-airborne wide field electromagnetic receiving system,which has good practical value and significance. |
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