| Frequency domain semi-airborne electromagnetic detection is widely used in underground space exploration,oil and gas exploration and other fields.It radiates electromagnetic signals with known frequency to space by using high-power ground transmitter.The unmanned aerial vehicle(UAV)is equipped with three component magnetic sensor and data acquisition unit to receive electromagnetic signal.It analyzes the underground structure by analyzing the collected magnetic field information.In engineering practice,the attenuation of electromagnetic signal is serious and the environmental noise is complex.In data processing,the original system uses superposition denoising and Fourier transform(FFT)to process the data.When the data length is short,the noise suppression ability of this processing method is poor.In addition,when the system is working,attitude noise will be introduced due to the change of sensor attitude,which will lead to the decline of signal quality of the system.To solve the above problems,a fast measurement and correction system of ground space frequency domain electromagnetic signal is designed.The main research contents are as follows:1.The current situation and development trend of semi-airborne electromagnetic detection system were analyzed in this dissertation.The structure and measurement principle of semi-airborne electromagnetic detection device were given.According to the layered earth model,the propagation mode and attenuation characteristics of electromagnetic wave in practical engineering were simulated.According to the existing three component magnetic sensor,the specific index of electromagnetic signal acquisition unit was given.2.The influence of FFT based data processing method on the system performance was studied in this dissertation.The design idea of electromagnetic signal receiving system based on phase-locked amplification technology was put forward.The influence of the orthogonality of different reference signals in the lock-in amplifier circuit on the measurement accuracy of the system was analyzed in this dissertation,and the simulation results of the lock-in amplifier circuit based on AD630 was given.3.On the basis of the layered earth model,the cause of attitude noise is analyzed.The influence of different attitude angle measurement errors on Z-component magnetic field correction results was calculated by simulation,and then the error requirements of attitude measurement system were obtained,that is,the measurement errors of roll angle and pitch angle were no more than ±0.1°,and the measurement errors of yaw angle were not required.4.The electromagnetic signal receiving system based on phase-locked amplification technology and the attitude measurement system based on MEMS(Micro-electro-Mechanical System)module were designed.The magnetic field information,roll angle and pitch angle can be measured.The attitude noise suppression algorithm was designed to achieve the attitude noise suppression.5.The circuit system test experiment and the whole laboratory internal experiment were designed,and the usability of the system was verified through data analysis.By improving the signal to noise ratio of the receiving system and increasing the measurement function of attitude angle,the accuracy of the semi-airborne electromagnetic detection system can be greatly improved,which provides a basis for the promotion of the semi-airborne electromagnetic detection system in the future. |
