均匀半空间CSAMT折线形线源的场源数值模拟

doi:10.11720/wtyht.2024.1103

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Abstract

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.

Key words： CSAMT non-linear ground cable source homogeneous half-space folded line source linear superposition

Received: 14 March 2023 Published: 26 February 2024

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	Yue-Quan DUAN
	Yun LIU
	Zi-Jun WANG
	Yu-Shan LI

Cite this article:

Yue-Quan DUAN,Yun LIU,Zi-Jun WANG, et al. Numerical simulation of the field source for the CSAMT folded line source in a homogeneous half-space[J]. Geophysical and Geochemical Exploration, 2024, 48(1): 151-161.

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https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2024.1103 OR https://www.wutanyuhuatan.com/EN/Y2024/V48/I1/151

Relative position of current line source and survey line
a—line source parallel to the survey line;b—line source is at an arbitrary azimuth angle with the survey line

Schematic diagram of the division of arbitrarily shaped current line source

The transmitting source is at an arbitrary azimuth angle to the survey line

Variation characteristics of apparent resistivity and impedance phase with frequency corresponding to different azimuth angles of transmitting source
a—variation curves of apparent resistivity with frequency at different azimuth angles; b—relative error curves of apparent resistivity at different azimuth angles; c—variation curves of impedance phase with frequency at different azimuth angles; d—absolute error curves of impedance phase at different azimuth angles

Variation characteristics of apparent resistivity and impedance phase with transmit-receiving distance corresponding to different azimuth angles of transmitting source
a—variation curves of apparent resistivity with transmit-receiving distance at different azimuth angles;b—relative error curves of apparent resistivity at different azimuth angles;c—variation curves of impedance phase with transmit-receiving distance at different azimuth angles;d—absolute error curves of impedance phase at different azimuth angles

Schematic diagram of folded line transmitting source models
a—transmitting source model a,the number of nodes is 4;b—transmitting source model b,the number of nodes is 5;c—transmitting source model c,the number of nodes is 6

Variation characteristics of apparent resistivity and impedance phase with frequency for different azimuth angles of folded line source
a—variation curves of apparent resistivity with frequency at different azimuth angles of folded line source; b—relative error curves of apparent resistivity at different azimuth angles of folded line source; c—variation curves of impedance phase with frequency at different azimuth angles of folded line source; d—absolute error curves of impedance phase at different azimuth angles of folded line sources

Variation characteristics of apparent resistivity and impedance phase with the transmit-receiving distance for different azimuth angles of folded line source
a—variation curves of apparent resistivity with transmit-receiving distance at different azimuth angles of folded line source; b—relative error curves of apparent resistivity at different azimuth angles of folded line source; c—variation curves of impedance phase with transmit-receiving distance at different azimuth angles of folded line source; d—absolute error curves of impedance phase at different azimuth angles of folded line sources

Apparent resistivity, impedance phase and error curves of folded line sources with different number of nodes
a—apparent resistivity curves of transmitting source models a, b and c;b—relative error curves of apparent resistivity between transmitting source models a, b and c;c—impedance phase curves of transmitting source models a, b and c;d—absolute error curves of impedance phase between transmitting source models a, b and c

Simplified schematic of folded line source
d—arbitrarily shaped folded line transmitting source model;e—simplified folded line transmitting source model

Comparison of apparent resistivity and impedance phase before and after simplification of folded line transmitting source model
a—apparent resistivity curves before and after transmitting source model simplification; b—relative error curve of apparent resistivity before and after transmitting source model simplification; c—impedance phase curves before and after transmitting source model simplification; d—absolute error curve of impedance phase before and after transmitting source model simplification

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