Design Of CSAMT Transmitted Signal Acquisition And Data Related Processing System

With the development of the national economy,the demand for the development of mineral resources is increasing.However,the storage of depletion for shallow mineral resources is decreasing,which makes mineral resource reserves in China can not meet the needs of the market economy.So that the fact above forces the development of geophysical exploration methods and related technologies toward greater depth detection and high-efficiency.At present,the widely used Controlled Source Audio-frequency Magnetotelluric Method(CSAMT)is an exploration method with deeper exploration depth in the frequency domain.However,in the actual exploration,the electromagnetic interference is serious and the response signal is always weak.During the process of effective information extraction,the noise pollution is serious,which greatly reduces the accuracy of underground information feedback.In order to solve this problem,the existing technical means are often concentrated on the data processing of the retrieved interpretation in the geophysical method.But when the data is interpreted directly by the noise interfered data,it will cause the distortion of the electromagnetic data,sometimes the electromagnetic data will be even wrong.And there are few studies on the pre-processing of data in CSAMT related methods.This paper aims at the above problem and the weak link of the research of CSAMT data pre-processing,independently researches and develops the CSAMT transmitted signal acquisition and data related processing system.Because of the mechanism of receiving signal response of CSAMT,that is,the received signal is the underground medium response information in the far zone that generated by the transmission system(electrical source),the transmitted data is the source information directly related to the received data,which is the theoretical basis for the important identification parameters.This paper based on the strong correlation between the received data and the transmitted signal,the randomness and non-correlation between the received data and the noise distribution,carrying out some technological innovation on the existing electrical apparatus and data acquisition,independently researches and develops the CSAMT transmitted signal acquisition and data related processing system.The system is combined with the broadband signal conditioning technology,high-resolution ADC sampling technology,FPGA digital logic control technology,data transmission technology based on USB2.0 protocol,GPS synchronization technology and weak signal detection technology.Through the complete and accurate collection of the transmitted data as the reference data,the received data can be processed based on the correlation detection method,so as to clearly identify the target signal,reduce the noise interference,and effectively improve the data processing efficiency.Based on the successful implementation of the above technologies,this paper has completed the testing analysis of various parts of the system,mainly including the performance test of transimitted signal acquisition part(50Hz wave detector function test,background noise test,GPS module test),CSAMT emission current measurement collection,related method feasibility test and field measured data test.The test results are as follows: Firstly the attenuation at the 50 Hz frequency point has reached 33.8dB,system background noise is-155 dB,and GPS function has implemented.Secondly the amplitude record accuracy error of the useful signal(square and sine wave)frequency is within ±10% in the typical signal test.Thirdly the PC show of the measured time domain waveform of the CSAMT emission current is consistent with the output image directly of the A622 by the oscilloscope,and the rms error of the time domain waveform is 6.7% of 10 times.Fourthly the deterministic signals of five groups of 64 Hz,512Hz,3200 Hz,4300Hz and 9600 Hz are selected to complete the comparison experiment between the correlation detection methods and the conventional FFT method,which proves the feasibility of the correlation detection method.Fifthly using the system described in the paper to get transimitted data in CSAMT to handle the synchronous received data file in the field measurement data test in the suburbs of Changchun,then using MATLAB in the upper computer to draw the visual resistance of “before and after treatment”,the comparison result shows that the overall curve is smoother after processing and there are no “flying point” existing.All of the results show that the CSAMT transmitted signal acquisition and data related processing system has reached performance index,the system can effectively improve the data quality,suppress the noise interference in the mineral exploration,and improve the data accuracy of the CSAMT detection system.