基于全相位FFT的电磁法有效相位信息提取

电磁法的相位相比于振幅,变化的幅度更大,在一定地质条件下具有更高的分辨能力。以往的研究一般采用传统加窗FFT(Fast Fourier Transformation)方法提取相位信息,该方法存在2个方面的缺点,首先是测量精度受频谱泄漏的影响比较严重,其次需要严格的“同步采样”。在实际应用中抗噪能力较差,导致无法获得有效的相位信息。为了提高抑制频谱泄漏能力,同时不受“同步采样”以及频率偏离的影响,采用全相位傅里叶变换方法进行了类脉冲、类充放电三角波、类方波以及高斯白噪声等典型干扰波形的仿真实验,结果表明:在同步采样的情况下,无论是否存在噪声干扰,传统的FFT方法与全相位傅里叶变换方法的相位测量误差均小于1%;而在非同步采样的情况下,传统FFT方法无法获得准确的相位值,而全相位FFT方法无论是否含有噪声干扰均能获得有效相位信息。因此,全相位FFT法具有传统加窗FFT法所具有的优点,能有效地抑制高斯噪声,对电磁法典型的干扰波噪声有着良好的抑制效果。

Effective Phase Information Extraction of Electromagnetic Method Based on All-phase FFT

Degree of phase change of electromagnetic method is greater than that of amplitude,and it has higher resolving power under certain geological conditions.In the past,the traditional FFT(Fast Fourier Transformation)method was used to obtain phase information.Eut there are two limitations in research on phase information of FFT.Firstly,the accuracy of measurement is seriously affected by spectrum leakage,and secondly,the synchronous sampling is needed.In practical applications,FFT also has the problem of poor noise immunity,which leads to the difficulty of using phase information.In order to improve the ability to suppress spectrum leakage and avoid the impact of synchronous sampling and frequency deviation,the all一phase Fourier transform method has been used to conduct the simulation experiments of typical disturbance waveforms such as impulse noise,trianglewave,squarewave,stepwave,white Gaussian noise.The results show that the phase measurement error of FFT and apFFT is usually less than 1%in synchronous sampling whether or not there is noise.The FFT cannot obtain accurate phase values in asynchronous sampling.The phase measurement error of apFFT is less than 0.00001% without noise in asynchronous sampling.The phase measurement error of apFFT is less than 1% with noise in asynchronous sampling.Therefore,the full-phase FFT method has the advantages of the traditional windowed FFT method,which can effectively suppress Gaussian noise and has a good suppression effect on the typical interference wave noise of electromagnetic method.