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| DATA PREPROCESSING AND WEAK SIGNAL DETECTION IN BOREHOLE MAGNETIC SURVEY |
| WANG Sai-xin1, LIU Tian-you1, OU Yang1, GAO Wen-li2, QIU Li-quan2, FENG Jie2 |
1. Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China;
2. Institute of Geophysical and Geochemical Exploration, CAGS, Langfang 065000, China |
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Abstract As the logging instrument is placed near the field source, the borehole magnetic data are likely to be affected by the internal magnetic field when the drill hole penetrates the magnetic body. As a result, the useful signal is often suppressed by strong jamming and not easy to identify. Therefore, it is important to find a method which can identify the weak signal through data preprocessing. In this paper, the methods for ground survey, called total horizontal derivate of tilt-angle and analytical Signal Amplitude, were used in borehole magnetic survey. The authors proposed vertical derivative of tilt-angle through coordinate transformation and a new method called Equalized Analytical Signal Amplitude. Through data processing of the model, the authors point out that the two kinds of methods can both identify the magnetic body and give the boundary information. The authors also give a standard to choose a suitable window to calculate the Equalized Analytical Signal Amplitude. The two kinds of methods were applied to Jiangsu ZK002 borehole magnetic data preprocessing. The vertical derivative of tilt-angle enlarged the interference of data, wheres the Equalized Analytical Signal Amplitude uses normalized method to identify the weak signal and suppress the interference. The Equalized Analytical Signal Amplitude is also well consistent with the results of magnetic susceptibility logging and the borehole data in ZK002.
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Received: 07 February 2013
Published: 10 February 2014
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