Improve the quality of "dead band" audio-frequency magnetotelluric impedance data using electric field remote reference
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摘要: 磁场远参考方法是大地电磁数据处理中最实用的噪声压制方法。音频大地电磁实际观测时，通常只采集一个测点的磁场而同步采集多个测点电场，往往没有同步的磁场数据进行远参考处理。而天然电磁场在5~1 kHz的“死频带”范围内信号强度较弱，导致该频段阻抗出现“飞点”。本文利用同步采集的电场对音频大地电磁数据进行电场远参考处理，结果发现：在“死频带”范围内，采用本地磁场和本地电场为参考时估算的阻抗在“死频带”分别会出现“上偏”和“下偏”，而以电场为参考可以明显提高“死频带”的阻抗质量；对不同参考距的实测数据处理表明，电场远参考处理的效果都要好于本地磁场和本地电场的处理效果，能够较好改善“死频带”数据质量，其效果与磁场远参考相当，对音频大地电磁野外数据处理具有重要的实际意义。Abstract: Magnetic remote-reference is the most practical noise suppression method in magnetotelluric data processing.In actual audio-frequency magnetotelluric (AMT) sounding observation, usually the "one with three" or "one with four" acquisition method is used, i.e., acquiring magnetic field of only one site and simultaneously acquiring electric field of multiple sites, without magnetic field data for remote-reference processing.The natural electro-magnetic field in the 5~1 kHz "dead band" range of signal strength is weak, resulting in the impedance in this band to have "outlies".In this paper, we found that the impedance estimated by using the local magnetic field and the local electric field as the reference in the "dead band" will be "upward" and "downward" biased respectively, while the electric field as the remote-reference channel can significantly improve the impedance quality in the "dead band".After processing the measured data of different reference distances, it is found that the effect of the electric field remote-reference processing is better than that of the local magnetic field and the local electric field.And the effect is comparable to that of magnetic field remote-reference.This has practical implications for AMT data processing.
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图 1 本地点与参考点不同距离时利用不同参考道估算阻抗得到的视电阻率-相位曲线
Figure 1. Apparent resistance and phase curves by estimating impedance from different reference channels with different distance between local site and the reference site
图 2 本地点与参考点相距90 km时，利用不同参考道估算阻抗得到的视电阻率和相位曲线
Figure 2. Apparent resistance and phase curves by estimating impedance from different reference channels with 90 km between local site and the reference site
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