The Research Of Time-frequency Analysis And Denoising Method In Airborne Transient Electromagnetic Data Processing

Airborne transient electromagnetic method(ATEM) is a quick survey ofconductive metal ore geophysical method, because of its high speed, low cost, largedetection range and other advantages, it has been a wide range of application inforeign countries now. As a result of the secondary field and the source is irrelevantand it can reflect the characteristics of the medium of underground. So it is mainly forthe processing and interpretation of the secondary field in the airborne exploration.However, the effective energy of the secondary field is weak, and is often subject tothe influence of various kinds of interference, which reduce the accuracy of the latterpart processing and interpretation. Therefore, it becomes an urgent problem to solve toseek a suitable filter or denoising method to eliminate the noise.In this paper,based on the863project “helicopter tower bird time domainairborne electromagnetic system exploration and practical research”(project number:2013AA063904),systematic analysis sources,characteristics and suppression methodof airborne transient electromagnetic noise, study for airborne transientelectromagnetic de-noising and evaluation methods,the main contents are as follows:Firstly, in this paper,the airborne transient electromagnetic noise characteristicsand the three major noise which affect the accuracy of data--electromagnetic noise,instrument and vibration noise, geological noise are investigated. And the mainsource,characteristics and de-noising method of those kinds of noise are summarized.Secondly, the theory,characteristics and the scope of application of threetime-frequency analysis--STFT,Gabor transform, Wigner-Ville distribution areanalyzed. By analyzing the analog data of airborne transient electromagnetic with the three methods to select a appropriate time-frequency method that can completelycharacteristic the characterization as the based method to process measured data.Thirdly, the effect of several window function to the STFT is mainly analyzed.Do time-frequency analysis in airborne transient electromagnetic signal with the sixdifferent window functions. Througth comparing the results, the best method tocharacterize the local signal characteristics can be selected, so that to provide theoptimal window function for later analysis.Fourthly, it analyzes the theory and characteristics of finite impulse responsedigital filter, LMS adaptive filtering, wavelet transform and with which to do datadenoising in airborne transient electromagnetic analog and measured. Combined withcharacteristics of the filtering methods to analyze the result of denoised.Finally, the idea of time-frequency analysis is first introduced in this paper,evaluate filtering method de-noising effect with time-frequency analysis andsignal-to-noise.Combined the time-frequency analysis and signal-to-noise ratio toevaluate denoising effect of the three filtering methods,then analysis the advantagesand disadvantages of denoised result in airborne transient electromagnetic signal.