| 周聪,伍师莹,汤井田,李杰,肖晓.论电场近区双频测深的可行性[J].矿产勘查,2024,15(9):1738-1749 |
| 论电场近区双频测深的可行性 |
| On the feasibility of electric field dual-frequency sounding in the near field of an electric dipole source |
| 投稿时间：2024-08-04 修订日期：2024-09-30 |
| DOI：10.20008/j.kckc.202409019 |
| 中文关键词: 电磁法 电磁测深 频率域 近区 广域 |
| 英文关键词: electromagnetic method electromagnetic sounding frequency domain near field wide field |
| 基金项目:本文受云南省重点研发计划“云南省西部重点矿集区成矿规律与找矿关键技术研究”项目（202303AA080006）和江西省自然科学基金项目（20232BAB203071）联合资助。 |
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| 中文摘要: |
| 非平面波区测深是频率域电磁勘探方法理论发展的重要动力。广域电磁法不对非平面波区电磁场表达式做简化，通过迭代求解获取全区视电阻率，极大拓展了人工源频率域电磁法的观测空间范围与探测深度。E-Ex模式是现今最为常用的广域电磁法观测模式，但其近区测深能力有限。本文探讨了两种广域电磁法E-Ex模式近区双频测深方案的可行性。首先，简述了高阶近似和低阶近似两种近区电场双频测深视电阻率计算方案的基本原理；然后采用一维模型进行数值模拟，对比了半空间模型中E-Ex模式不同场成分的强度与感应数的关系，计算了典型地电模型的视电阻率，分析了频率间隔及观测误差等对计算结果的影响。结果表明：高阶近似方案基本不具备可行性；低阶近似双频测深方案在理想条件下可以获得近区地电介质的变化信息，对地下低阻层反映更为灵敏，受观测角度、接地导线偶极长度及观测频率间隔等因素影响均较小，但对观测数据误差极为敏感，观测总场中较小的误差也将导致近区视电阻率信息提取失败。因此，广域电磁法E-Ex模式近区双频测深方案实际应用的关键在于控制观测精度。 |
| 英文摘要: |
| Sounding in the non-plane wave region is an important driving force for the theoretical development of frequency domain electromagnetic exploration methods. The wide field electromagnetic method does not simplify the theoretical expression of the electromagnetic field in the non-plane wave region， and obtains the apparent resistivity of the full region through iterative solution， which greatly expands the observation space range and detection depth of the controlled source frequency domain electromagnetic method. E-Ex model is the most commonly used wide field electromagnetic observation model， but its near field sounding ability is limited. In this paper， the feasibility of two near field dual-frequency sounding schemes of E-Ex mode for the wide field electromagnetic method is discussed. Firstly， the basic principles of two schemes， the so-called high order and low-order approximation， for calculating the apparent resistivity of near field dual-frequency sounding are described briefly. Then an one-dimensional model is used for numerical simulation， and the relationship between the intensity of different field components which vary with the induction number is compared in the half-space model. The apparent resistivity of typical geoelectric model is calculated， and the influence of frequency interval and observation error on the calculation results is analyzed. The results show that the higher order approximation scheme is not feasible. Under ideal conditions， the low-order approximate dual-frequency sounding scheme can obtain the variation of the geoelectric information in the near field， which is more sensitive to the underground low resistivity layer， and is less affected by the observation angle， the length of the grounding wire dipole and the observation frequency interval. However， it is very sensitive to the error of observation data， and the small error in the total observation field will also lead to the failure of extracting the near field apparent resistivity information. Therefore， controlling the observation accuracy is the key to the practical application of the near field electric field dual-frequency sounding methods. |
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