时间域航空电磁数据线圈运动噪声去除方法仿真研究

Simulation Research on Coil Motion Noise Removal for Time Domain Airborne Electromagnetic Data

时间域航空电磁探测中,接收线圈在地磁场中的运动产生感应电动势,形成线圈运动噪声,因其幅度较大而成为航空电磁探测中的主要噪声源之一。线圈运动噪声具有低频特性,虽然幅度随频率增大而迅速衰减,但仍然含有高于发射基频的频率成分;因此,传统的高通滤波器在处理线圈运动噪声中存在一定的局限性。根据航空电磁数据的特点,采用多项式拟合全波半周期运动噪声,运用拉格朗日优化算法求解运动噪声多项式系数,并将其从半周期电磁数据中去掉以达到去除噪声的目的。通过仿真实测数据的运动噪声压制实验,对比分析了多项式拟合法与传统高通滤波器法的线圈运动噪声去除能力。仿真结果表明,多项式拟合法能够有效去除航空电磁数据中的线圈运动噪声,提高信噪比超过40 dB。

In the course of time domain airborne electromagnetic exploration, induction electromotive force is produced by the movement of the receiver coil in the earth＇s magnetic field, which is the main noise source in AEM data because of its large amplitude. Coil motion noise covers mainly low frequency band. Though its amplitude will rapidly decreases with frequency increasing, it still contains higher frequency components than transmitting frequency. Therefore, the traditional high pass filter has certain limitation in dealing with coil motion noise. According to the airborne electromagnetic data characteristics, polynomial is used to approximate motion noise for each full waveform half cycle, and then Lagrange method is employed to solve polynomial coefficient of motion noise. The polynomial coefficients are calculated by matrix inverse and finally motion noise is subtracted from each half cycle electromagnetic data. Furthermore, polynomial approximation method is applied to the synthetic data contaminated by low frequency motion noise comparing with traditional high pass filter method. Simulation results indicated that, with coil motion noise of airborne the polynomial approximation method shows more electromagnetic data, which can increase the signal effective in dealing to noise ratio more than 40 dB.