多通道瞬变电磁法激励源降噪性能对比研究

Comparative study on noise reduction performance of MTEM sources

对比研究双极性方波与m序列两种激励源在多通道瞬变电磁法(Multi-Transient Electromagnetic,MTEM)中的降噪性能,将大地脉冲响应的提取等效为辨识滤波器输出,通过分析辨识滤波器的谱特性量化评估不同激励源的降噪性能;通过数值模拟讨论两种激励源信号在工频噪声与白噪声环境下的大地脉冲响应辨识精度,模拟结果表明使用m序列替代双极性方波作为激励源能够大幅提高辨识精度,且残留噪声集中在码元频率及其谐频处;设计野外对比试验,采集两种激励源在弱/强干扰下的响应信号进行大地脉冲响应辨识,试验结果表明弱干扰环境下两种激励源的辨识精度相近,强干扰环境下m序列的降噪性能高于双极性方波,且噪声残留特征与数值模拟吻合.

The purpose of this paper is to compare the noise reduction of m-sequence and bipolar square-wave sources which commonly used in Multi-Transient Electromagnetic(MTEM) surveys. The concept of deconvolution filter was proposed to achieve quantitative analysis of the noise reduction in MTEM method. A numerical simulation was conducted to discuss the identification accuracy of two sources in the power-frequency noise environment and Gaussian white noise environment, which gave the inference that m-sequence achieve better noise reduction and the residual noise concentrate in the coding frequency and its harmonics. A further contrast experiment was conducted, two data sets with extremely different Signal-to-Noise Ratio(SNR) were discussed. The identification accuracy of the two sources is similar in the weak noise environment, and the noise reduction of m-sequence in the strong noise environment is higher than that of bipolar square-wave, which was consistent with the simulation results.