For field surveys using the controlled source audio magnetotelluric (CSAMT) method, it is generally believed that the CSAMT line source is a simplified electric dipole source with a minimal length. However, CSAMT line sources are all arranged in a folded line pattern in field surveys. Based on the previous research results, this study derived the numerical calculation method for the electromagnetic field excited by the folded line source according to the linear superposition principle of electromagnetic fields. Through the calculation of different folded line source models, this study analyzed the influences of the folded line source on the apparent resistivity and impedance phase curves in the homogeneous half-space. Model calculations demonstrate that the folded line source significantly influenced the near and transition zones of the apparent resistivity and impedance phase curves but had no influence on their far zones. The influences on the near and transition zones were primarily caused by the azimuths of folded line segments, and higher azimuths were associated with more significant influences on the apparent resistivity and impedance phase of survey points. In the case of very low azimuth angles, the folded line source can be approximated as a straight line source for processing, improving the work efficiency while fully considering the morphology of the emission source. This study provides theoretical support for the near-field correction of subsequent CSAMT data processing and the CSAMT numerical simulation.
段跃权, 刘云, 王紫郡, 李雨珊. 均匀半空间CSAMT折线形线源的场源数值模拟[J]. 物探与化探, 2024, 48(1): 151-161.
DUAN Yue-Quan, LIU Yun, WANG Zi-Jun, LI Yu-Shan. Numerical simulation of the field source for the CSAMT folded line source in a homogeneous half-space. Geophysical and Geochemical Exploration, 2024, 48(1): 151-161.
Goldstein M A, Strangway D W. Audio-frequency magnetotellurics with a grounded electric dipole source[J]. Geophysics, 1975, 40(4):669-683.
doi: 10.1190/1.1440558
[2]
Grandis H, Sumintadireja P. A brief review for the proper application of magnetotelluric (MT) and controlled-source audio-frequency magnetotelluric (CSAMT) in geothermal exploration[C]// 12nd annual indonesian geothermal association meeting and conference, 2012.
[3]
Di Q Y, Fu C M, An Z G, et al. An application of CSAMT for detecting weak geological structures near the deeply buried long tunnel of the Shijiazhuang-Taiyuan passenger railway line in the Taihang Mountains[J]. Engineering Geology, 2020, 268:105517.
doi: 10.1016/j.enggeo.2020.105517
[4]
Wang G, Lei D, Zhang Z Y, et al. Tensor CSAMT and AMT studies of the xiarihamu Ni-Cu sulfide deposit in Qinghai,China[J]. Journal of Applied Geophysics, 2018, 159:795-802.
doi: 10.1016/j.jappgeo.2018.09.031
[5]
Streich R. Controlled-source electromagnetic approaches for hydrocarbon exploration and monitoring on land[J]. Surveys in Geophysics, 2016, 37(1):47-80.
doi: 10.1007/s10712-015-9336-0
Di Q Y, Xue G Q, Yin C C, et al. New methods of controlled-source electromagnetic detection in China[J]. Scientia Sinica:Terrae, 2020, 50(9):1219-1227.
doi: 10.1360/SSTe-2019-0162
[7]
何继善. 可控源音频大地电磁法[M]. 长沙: 中南工业大学出版社,1990.
[7]
He J S. Controlled source audio magnetotelluric method[M]. Changsha: Central South University of Technology Press,1990.
Han Y H, Shen X L, Li B, et al. Target area prediction and drilling verification of the tectonic fissure-hosted geothermal water in Meixian County,Guanzhong Plain based on the integrated geophysical exploration[J]. Geophysical and Geochemical Exploration, 2023, 47(1):65-72.
Wang J C, Zhao Z G, Gao S Y, et al. Application of a comprehensive geophysical exploration methods in the exploration of geothermal resources in Yueliangwan,Binhai County[J]. Geophysical and Geochemical Exploration, 2023, 47(2):321-330.
Liu C W, Wang C, Hu C P, et al. Application of a comprehensive geophysical exploration methods to water exploration in magmatic rock mountainous areas with water shortage in Jiaodong Peninsula[J]. Geophysical and Geochemical Exploration, 2023, 47(2):512-522.
[11]
Wang J L, Lin P R, Wang M, et al. A multiple parameter extraction and electromagnetic coupling correction technique for time domain induced polarisation full waveform data[J]. Exploration Geophysics, 2019, 50:113-123.
doi: 10.1080/08123985.2019.1584014
Chen W Y, Xue G Q, Cui J W. Analysis on the influence from the shape of electric source TEM transmitter[J]. Progress in Geophysics, 2015, 30(1):126-132.
Li Z H, Huang Q H. 1D forward modeling and inversion algorithm for grounded galvanic source TEM sounding with an arbitrary horizontal wire[J]. Progress in Geophysics, 2018, 33(4):1515-1525.
Wang P F, Wang S M, An Y N. One-dimensional smoke ring inversion of irregular loop source transient electromagnetic method[J]. Progress in Geophysics, 2019, 34(3):1113-1120.
Li J P, Li T L, Zhang Y D. Tem forward and inversion of arbitrary shape loop source in layered media[J]. Geophysical and Geochemical Exploration, 2012, 36(2):256-259.
Li J P, Li T L, Zhao X F, et al. Study on the TEM all-time apparent resistivity of arbitrary shape loop source over the layered medium[J]. Progress in Geophysics, 2007, 22(6):1777-1780.
Li J P, Li T L, Zhang H, et al. Study and application of the TEM forward and inversion problem of irregular loop source over the layered medium[J]. Journal of Jiling University:Earth Science Edition, 2005, 35(6):790-795.
Zhang B, Tan H D. The two-dimensional csamt modeling with topography[J]. Geophysical and Geochemical Exploration, 2014, 38(1):151-156.
[24]
Xiong Z T, Tang X G, Li D D, et al. Linear source CSAMT response simulation in the 2D anisotropic formation with topography[J]. Journal of Applied Geophysics, 2019, 171:103861.
doi: 10.1016/j.jappgeo.2019.103861
Chen X B, Zhao G Z. Study on the transmitting mechanism of CSELF waves:Response of the alternating current point source in the uniform space[J]. Chinese Journal of Geophysics, 2009, 52(8):2158-2164.
Liu D Y, Xu K J, Zhao G M, et al. The study of three-dimensional geo-electric field of arbitrary shape line sources[J]. Progress in Geophysics, 2006, 21(2):395-399.
Su W, Li D J, Weng A H. Characteristics of the electric field generated by a finite-length-ground wire source in homogeneous half-space[J]. Geology and Exploration, 2019, 55(3):801-808.
[28]
Nabighian M. Electromagnetic methods in applied geophysics[M]. Tulsa: Society of Exploration Geophysicists,1988.
[29]
徐士良. 计算机常用算法[M]. 北京: 清华大学出版社,1995.
[29]
Xu S L. Common computer algorithms[M]. Beijing: Tsinghua University Press,1995.
Liu Y, Song T, Wang Y. A digital filter method for evaluating the fixed-loop transient electromagnetic field[J]. Computing Techniques for Geophysical and Geochemical Exploration, 2016, 38(4):437-442.
He G Y, Gao Y L. Visual Fortran commonly used numerical algorithm set[M]. Beijing: Science Press, 2002.
[32]
Wang X X, Deng J Z. A comparative study on the difference between the multi-dipole sources and vector synthesis source[J]. Journal of Environmental and Engineering Geophysics, 2020, 25(4):529-543.
doi: 10.32389/JEEG20-012
