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| The calculation of full time apparent resistivity for transient electromagnetic survey based on “double smoking ring” theory |
| Xu Yangcheng1, Wu Yan-qing1, CUI Ren2, HAN Shuang1 |
1. China Coal Technology Engineering Group Chongqing Research Institute, Chongqing 400039, China;
2. No. 136 Geological Party, Chongqing 400039, China |
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Abstract Owing to the impact of inductor and capacitor of transmit coil, the transmit current of transient electromagnetic turns off like the ramp current. If we use the "single smoke ring" theory which fits for step turning off transmit current to make interpretation, the distortion will occur during the early and middle stage. According to the expression of second field induced voltage for ramp current, this paper presents interpretation with the "double smoke ring" theory, i.e., the secondary field induced voltage is made to be equivalent to the summation of secondary magnetic induction excited by two equal, opposite and successive "smoke ring" after the current is completely turned off. The secondary magnetic induction excited by every "single smoke ring" is calculated with forward and backward recurrence respectively. After that, the monotony of secondary magnetic induction excited by "smoke ring" is utilized to calculate the full-time apparent resistivity of ramp current and remove the distortion. At last, the numerical simulation model is used to confirm the correctness. The results obtained by the authors provide theoretical support for the full-time transient electromagnetic exploration and explanation.
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Received: 20 May 2013
Published: 10 June 2014
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