我要发布一个部分答案现在,它需要更多的阅读整理一个完整的解释。中描述的问题有两个类似的线圈,一个交流磁场辐射(“发射器”),另一个拿起弱辐射AC地下电流产生的磁场引起的主要领域。灵敏度与深度,有两种操作模式。以下两个数据来自4.1节(GEONICS Technical note # 6;以低感应电磁地形电导率测量数字)(http://www.geonics.com/pdfs/technicalnotes/tn6.pdf)。(更多技术注释[这](http://www.geonics.com/html/technicalnotes.html))在这两个人物这两个线圈是由一个水平距离分开年代美元通常几米。在* *水平模式* *两个线圈的轴在水平面。在这个方向敏感性总是表面附近的山峰,和下降到30%左右的深度s $ 0.4美元。!(电磁地形电导率测量)(https://i.stack.imgur.com/c2BmX.png)在垂直模式* * * *两个线圈的轴点“向上”或垂直。在这个方向灵敏度低表面*和山峰*深度附近的$ 0.4新元。  In either case, if $s$ is twice as big (the coils are twice as far apart) these two shapes will be stretched by the same amount. If $s$ is 2 meters, the vertical method will have peak sensitivity at 0.8 meters. If $s$ is 5 meters, vertical sensitivity peaks at 2.0 meters. The two plots can be seen on the right side of Figure 1. in [The Application of EM38: Determination of Soil Parameters, Selection of Soil Sampling Points and Use in Agriculture and Archaeology](https://www.mdpi.com/1424-8220/17/11/2540/htm) Kurt Heil and Urs Schmidhalter, Sensors 2017, 17(11), 2540; https://doi.org/10.3390/s17112540 That article also links to [Comparison of the EM38 and EM38-MK2 electromagnetic induction-based sensors for spatial soil analysis at field scale](https://www.sciencedirect.com/science/article/pii/S0168169914002968) which may cite further references but it's paywalled.  >Figure 1. (Left) Relative cumulative contribution vs depth for vertically (RV(z)) and horizontally (RH(z)) orientated dipoles; (Right) Comparison of the relative responses for vertically (FV(z)) and horizontally (FH(z)) oriented dipoles. Yes, that's all fine and dandy... But Why? -- I can't come up with a simple model for why this is true, so I'll have to read further. It's possible someone else will be able to provide a better answer. I think it's related to how the phase of the signals are process, but I'm not sure about that yet. However, the Computers and Electronics in Agriculture paper [Accuracy issues in electromagnetic induction sensing of soil electrical conductivity for precision agriculture](https://www.sciencedirect.com/science/article/pii/S016816990000185X) (also available [here](http://extension.missouri.edu/sare/documents/EMImethods2002.pdf)) K.A.Sudduth, S.T.Drummond and N.R.Kitchen, Volume 31, Issue 3, May 2001, Pages 239-264 https://doi.org/10.1016/S0168-1699(00)00185-X happens to give equations for these shape, and a clue to where these are from.  Those equations are close but $\color{red}{wrong!!}$ they are missing a division "/" sign. >Fig. 2. Relative response of EM38 sensor as a function of distance (adapted from McNeill, 1992). The equations in the figure have obviously been typed incorrectly, but if I make some simple adjustments they work nicely $$\phi_V(z) = \frac{4z}{(4z^2+1)^{3/2}} $$ $$\phi_H(z) = 2 - \frac{4z}{(4z^2+1)^{1/2}} $$ where z has to be unitless, so is almost certainly given by: $$z \equiv \frac{\text{depth}}{s}$$ where $s$ is the separation between the two coils as before.  Possibly helpful links: -- - [The use of electromagnetic induction techniques in soils studies](https://www.sciencedirect.com/science/article/pii/S0016706114000548) (also available [here](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2462&context=usdaarsfacpub))