ERT - Session 5: Forward Modeling of Resistivity Data with Res2dmod software
ฝัง
- เผยแพร่เมื่อ 13 ต.ค. 2024
- Electrical Resistivity Tomography (ERT) - from Zero to Hero
Session 5: Forward vs. Inverse Modeling together with 2D Forward Modeling of Resistivity Data by Res2dmod
Forward Modeling vs. Inverse Modeling (Inversion)
Non-uniqueness
How to create Res2dmod input file
Working with Res2dmod software
The presentation file is available at:
drive.google.c...
Res2dmod free software is available at:
www.geotomosof...
Download link:
www.geotomosof...
As topography has a noticeable effect on resistivity model response, it is highly recommended to check the video entitled "Res2dmod Software - Incorporation of topography into forward model" in link below:
• Res2dmod Software Tuto...
Watch the whole video series (playlist) step by step to have a solid background on ERT, even if you are somehow familiar with ERT. There are some important points in each one.
If you have any enquiries, contact me by email.
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Thank you very much. Sir
Merci Sayyed :)
Hello Sir,
First of all thank you very much for all your session. It is very useful for my thesis.
I have a question : if i had 126 electrodes spaced by 5m in a dipole-dipole array, what should i enter in the window "Choose array type" ?
Number of 'a' spacing = ?
Number of 'a' spacing = ?
Number of 'n' values = ?
Maximum geometric factor = 2000 as well ?
Maximum depth of investigation as ration of line lenght = ?
Thank you for your feedback.
I want to emphasize that res2dmod is a forward modeling program
(I think that you have misunderstood; forward modeling vs. inverse modeling).
If you have a series of measurements from the field /study area and want to estimate the variations in the subsurface, you must do inverse modeling / inversion i.e. the opposite of forward modeling.
If you do want to perform a forward modeling, you should define your array characteristics accordingly.
For example, you want to test the effectiveness / feasibility of using two "a spacing"s in your dipole dipole array. For instance, the following situations: (1) combination of a=2m and a=4m (2) a=4m.
Then, you create your forward models for (1) and (2) scenarios separately and you examine their effectiveness for the same target/anomaly (your desired target).
I hope these comments would be useful.
If you follow the ERT sessions in order, I don't think that you have any serious question or problem (if you had any questions, just ask in a comment and I will help as much as I can).
@@OneGeoscientist Thank you for your quick response. I'm sorry I wasn't clear enough. The point is, I took ERT measurements with a dipole dipole array and with an electrode spacing of 5m. After that, I did the inversion of the ERT data by using Res2Dinv. Now what I wanna do is make a model from my field measurement tomography, and I would have to invert the data from this model to get a tomography that most closely matches the tomography that I did with measurements taken in the field.
Now my issue is that : i don't know what to write in the window "choose array type" in Res2Dmod. Number of 'a' spacing is 5 in my case ? and number of 'n' values is 1 in my case ? I may not understand what the "a" and the "n" correspond to.
thank you.
Hello Sir. I need your help. i still confuse to utilize the method of data preparing. Ex: in our equipment, we have number electrodes 56, spacing 5m, and if i use Dipole-dipole Array. 1. how to calculate the Number of Pseudosection data level? 2. explain how to calculate the line 13 and 14.
i hope to see your feedback zoo.
Thank you very much.
Here are some details. I hope it helps you.
Line 13: Depth to horizontal grid mesh.
The first value would be usually in the range of 0.1-0.5*(smallest pseudo-depth). There is no strict rule but it should definitely be smaller than smallest pseudo-depth.
For example, for unit electrode spacing 2m, smallest pseudo-depth for various arrays would be:
schlumberger= (0.519*2)~1m.
dipole-dipole= (0.416*2)~0.8m
pole-pole=(0.867*2)~1.7m
Thus, 0.4m would be a nice choice. Smaller values would be used but it may limit your modeling options for deeper targets. It also creates irregular rectangular blocks (i.e. 2m*0.1m seems not good). If you want smaller details, you have to consider smaller values for unit electrode spacing, which in turn, also affects depth of grid mesh.
About the increment, you can set equally-spaced values or increase them towards depth (such as I did in the video). It is a matter of preference and equally-spaced models would be better in some cases.
Line 14 up to end: resistivity of your cell/blocks
Good Luck
thank you so mush for the video u have no idea how mush u helped me but i cant find the pfd support
In the link that I have mentioned for downloading the res2dmod, you can find the pdf manual inside one of the zip files:
www.geotomosoft.com/r2dmodwin.zip
Thanks for sharing. I don't understand yet, how to get the values for the 13th line, there is some formula for getting it?
Hi. Read all of the comments. Somebody asked the same question.
Hope it helps.
Hello Sir,
Can VES data be converted into 2D using any software. We have conducted VES survey in parallel sections by leaving a few 100 of metres distance between each survey.. we have conducted 3 surveys in same parallel sections and 2 more perpendicular to this area.. So will be possible to get 2D pseudosections
Hi.
First, I advise you to watch session 4 as you are using some incorrect terminology.
th-cam.com/video/7yaf8TddeU4/w-d-xo.html
Second, the answer is "Yes". It is possible to invert VES in 2D. However, you should be careful that your model is reliable/realistic and not one of the million possible models that can satisfy your data (non-uniqueness). It is not easy to discuss but you may find some clue by watching the next sessions of ERT as I have discussed a problem similar to the thing that can happen in 2D inversion of VES.
hello Sir ! think you for this greatful video please how can I find this software ?
the download link is in the description of the video
Thank you very much. Sir