Study On FIR Digital Filtering Technology In Wide Field Electromagnetic Effective Signal Extracting

Wide field electromagnetic method, a new kind of artificial source frequency domain electromagnetic sounding method, is proposed by Academician He Ji-shan recently, Central South University. It defines wild field apparent resistivity which just needs to measure one component of the electromagnetic fields on wild working and there is no limitations of remote area measurement; it can get electromagnetic information of multiple depth at one measurement by using pseudo-random signal as artificial source signal, which improve accuracy and efficiency of the measurement. The method is effective in oil and gas exploration,metal mine exploration and deeper earth exploration. But the electromagnetic field characteristics and the undeveloped data processing lead Wide field electromagnetic method has low signal resolution, it is very important that gain reliable electromagnetic response functions by extracting effective signal and improving data SNR. In this paper,analyzing features of time series and data processing requirements, a method based on the Finite Impulse Response (FIR) digital filtering technology is raised to extract effective signal.The paper introduces the basic principle of wide field electromagnetic method, and analyzes the characteristic of pseudo-random signal; analyzes the power spectrum of signal or noise and defects of digital extraction technology by considering the measured data, we discuss filter performance indicators and researched the corresponding algorithm.This paper designed the filter of narrow-band FIR based on theories of sampling rate signal processing,which carried on sampling to the signal such as anti-aliasing filtering and decimator. The paper analyzed its characteristics,such as frequencies response and anti-aliasing,the results indicate that this method can efficiently control the performance of narrow band FIR filters, which conclude width of pass-band,attenuation of stop-band and cut off frequency.Through the simulation and analysis based on Matlab, the noise outside the main frequency has been filtered, signal has reflected and the data quality has been improved significantly.