+Hi Reza, just a note on what a resistivity "contrast" is. For a 2-layer case (resistivity p1 for overburden, p2 for bedrock) it is the reflection coefficient i.e.(p2-p1)/(p2-p1). If this ratio is more than about 30, the resolution saturates and the method cannot distinguish between two high values of bedrock resistivity. So, paradoxically, the resistivity method is very sensitive to relatively small contrasts and insensitive to large ones. This applies to the modelling in 2D and 3D. In fact if you look at 1-D soundings, and increase the resistivity of the second layer, you will see it asymptotically approach a limit. The only way to see large contrasts is to use MT as 1D soundings or 2D profiles with FE inversion.
Hi Thank you for the comment. You probably meant (p2-p1)/(p2+p1)…? :) I am not a modeling guy but I get your point Distinguishing 10000 vs 100000 ohm meter interface should be difficult or maybe impossible (or 1 and 0.1 ohm.m interface when looking at conductive cases) and that can also be a reason that you also reach your measurement accuracy limits (?) and very low SNR But I of course consider common or usual cases that you usually face on the ground But good comment, thanks for sharing
@@OneGeoscientist Yes, well spotted! If the overburden (where the electrodes are emplaced) is 100 ohm-m, and the bedrock resistivity values on each side of a vertical contact below the overburden layer are 3,000 and 10,000 ohm-m, there will be no difference in the apparent resistivity measured on the surface above that contact. as both sides will be >= 30x the overburden resistivity. It is a function of the fractional current flow in the upper and lower media, not just measurement accuracy or SNR. This is actually a fairly common situation, especially where conductive tropical or glacial overburden overlies resistive granitic or metamorphic rocks. The problem is that as it is cannot be seen in the data, it is not suspected!
Hi Reza Great course. I really appreciate what you have done to prepare this mini-course. May I ask what the name of books or lecture notes you mentioned in this session was?
Hallo What are the best ways to explore the quality of groundwater for a depth of more than 150 m using the two-dimensional method while avoiding the dispersal of the current with depth
Hi. Please be specific and precise when you ask your question. What do you mean by "quality of groundwater" and what is its relationship with ERT? avoiding dispersal of current with depth??? First of all, if you want to look "deep" into the earth by ERT, you must try to have electrical currents deep into the ground (the main guide is sensitivity function since current penetration is not always directly proportional to depth of investigation), otherwise, you won't be able to recognize the resistivity variations in the deep subsurface. (i.e. if current is not passing through the material you won't be able to measure its electrical properties). Secondly, in earth sciences, you have to consider a suitable strategy for each situation/problem. thus, you have to design array, set proper unit electrode spacing, etc. to achieve your goal. I haven't worked on deep groundwater projects but as far as I am concerned, you may use any array that can present a reliable resistivity of deep targets such as wenner, pole-dipole, schlumberger, etc. I hope it helps. Good luck.
Sir what is the book you recommended of 2014 and the tutorial Site.. for learning inversion.. please share the links if possible.. And Sir, could you please explain, the transverse resistance, longitudinal conductance-related anisotropies that are encountered.. Thank You
Thanks for your comments. I have forgotten this one. The main references are now added to the first video (openning session). Please look at the description of this video: ruclips.net/video/NWelvffyUpc/видео.html The concepts such as transverse resistance (RT), etc. that you mentioned are mainly related to 1D resistivity surveying (Vertical Electrical Sounding ; VES) which is not my focus in this video series. So, i am not possibly cover them soon, i.e. in this video series. I assume you are working in the groundwater hydrology / hydrogeophysics domain. Thus, if you are working with VES data a lot, i strongly suggest you to read one of my papers which is a good overview of some problematic situations in VES data analysis. As RT requires good geophysical models as input, i think that paper would be helpful for your career. Here is the paper link: www.researchgate.net/publication/337027654_Assessing_the_effects_of_1D_assumption_violation_in_vertical_electrical_sounding_VES_data_processing_and_interpretation I will also be available if you had any further questions after reading the paper (you can email me; if I didn't responded your email due to missing it, you can comment here in youtube) Don't forget to share this channel with your friends that might be interested in geoscientific topics. :)
Thank you for your comment. This is an easy question to ask but it is not simple to answer. Detection of the depth to "groundwater level" is not possible in many cases because "resistivity contrast" and "resolution at depth" are not often sufficient to be able to affect recorded resistivity data. Thus, the groundwater level or thickness of water-saturated zone is often questionable or in best cases, tricky to find. In addition, the violation of 1D assumption would be a severe problem in VES data analysis because it can occur in many cases in the field (despite the face that we presume the 1D assumption is correct). I suggest you to have a look at my paper (available in the link below) to read a relatively comprehensive discussion on this problem: www.researchgate.net/publication/337027654_Assessing_the_effects_of_1D_assumption_violation_in_vertical_electrical_sounding_VES_data_processing_and_interpretation/citations I hope it helps you. Good Luck.
Hi If you follow the ERT sessions from session 1 to session 5, you will get a nice idea about resistivity, inversion, etc. Follow ERT playlist in this channel
+Hi Reza, just a note on what a resistivity "contrast" is. For a 2-layer case (resistivity p1 for overburden, p2 for bedrock) it is the reflection coefficient i.e.(p2-p1)/(p2-p1). If this ratio is more than about 30, the resolution saturates and the method cannot distinguish between two high values of bedrock resistivity. So, paradoxically, the resistivity method is very sensitive to relatively small contrasts and insensitive to large ones. This applies to the modelling in 2D and 3D. In fact if you look at 1-D soundings, and increase the resistivity of the second layer, you will see it asymptotically approach a limit. The only way to see large contrasts is to use MT as 1D soundings or 2D profiles with FE inversion.
Hi
Thank you for the comment.
You probably meant (p2-p1)/(p2+p1)…? :)
I am not a modeling guy but I get your point
Distinguishing 10000 vs 100000 ohm meter interface should be difficult or maybe impossible (or 1 and 0.1 ohm.m interface when looking at conductive cases) and that can also be a reason that you also reach your measurement accuracy limits (?) and very low SNR
But I of course consider common or usual cases that you usually face on the ground
But good comment, thanks for sharing
@@OneGeoscientist Yes, well spotted! If the overburden (where the electrodes are emplaced) is 100 ohm-m, and the bedrock resistivity values on each side of a vertical contact below the overburden layer are 3,000 and 10,000 ohm-m, there will be no difference in the apparent resistivity measured on the surface above that contact. as both sides will be >= 30x the overburden resistivity.
It is a function of the fractional current flow in the upper and lower media, not just measurement accuracy or SNR.
This is actually a fairly common situation, especially where conductive tropical or glacial overburden overlies resistive granitic or metamorphic rocks. The problem is that as it is cannot be seen in the data, it is not suspected!
Dude next level 🤩 rocking delivery
Thanks for sharing your knowledge. You have a great didatics.
thnkz alot sir
I'm v.glad to get a channel like yours
teşekkür ederim gerçekten
Hi Reza
Great course. I really appreciate what you have done to prepare this mini-course. May I ask what the name of books or lecture notes you mentioned in this session was?
Hi
They are mainly from:
Geophysics for the mineral exploration geoscientists
geotomosoft.com/coursenotes.zip
Thank you sir
Hello, please tell the prerequisite playlist you told to watch about dr rook. I cant find it
Dr Loke's notes not videos.
www.geotomosoft.com/coursenotes.zip
Many thanks sir.
Sir please explain how we can integrate our ERT/ERS results with the ground image as you present in one of the title images at the start of the video.
That is just for the sake of beauty as it was possible due to the cliff. That is done in corel draw (same as photoshop).
hi, i think you missed the equatorial dipole-dipole array :)
Maybe. ;)
There are also some stumbles in almost all videos but I will try to improve my presentation in next videos.
😊😁
Maam?
Hallo What are the best ways to explore the quality of groundwater for a depth of more than 150 m using the two-dimensional method while avoiding the dispersal of the current with depth
Hi.
Please be specific and precise when you ask your question.
What do you mean by "quality of groundwater" and what is its relationship with ERT?
avoiding dispersal of current with depth???
First of all, if you want to look "deep" into the earth by ERT, you must try to have electrical currents deep into the ground (the main guide is sensitivity function since current penetration is not always directly proportional to depth of investigation), otherwise, you won't be able to recognize the resistivity variations in the deep subsurface. (i.e. if current is not passing through the material you won't be able to measure its electrical properties).
Secondly, in earth sciences, you have to consider a suitable strategy for each situation/problem. thus, you have to design array, set proper unit electrode spacing, etc. to achieve your goal. I haven't worked on deep groundwater projects but as far as I am concerned, you may use any array that can present a reliable resistivity of deep targets such as wenner, pole-dipole, schlumberger, etc.
I hope it helps.
Good luck.
Sir what is the book you recommended of 2014 and the tutorial Site.. for learning inversion.. please share the links if possible..
And Sir, could you please explain, the transverse resistance, longitudinal conductance-related anisotropies that are encountered..
Thank You
Thanks for your comments. I have forgotten this one.
The main references are now added to the first video (openning session). Please look at the description of this video:
ruclips.net/video/NWelvffyUpc/видео.html
The concepts such as transverse resistance (RT), etc. that you mentioned are mainly related to 1D resistivity surveying (Vertical Electrical Sounding ; VES) which is not my focus in this video series. So, i am not possibly cover them soon, i.e. in this video series.
I assume you are working in the groundwater hydrology / hydrogeophysics domain. Thus, if you are working with VES data a lot, i strongly suggest you to read one of my papers which is a good overview of some problematic situations in VES data analysis. As RT requires good geophysical models as input, i think that paper would be helpful for your career. Here is the paper link:
www.researchgate.net/publication/337027654_Assessing_the_effects_of_1D_assumption_violation_in_vertical_electrical_sounding_VES_data_processing_and_interpretation
I will also be available if you had any further questions after reading the paper (you can email me; if I didn't responded your email due to missing it, you can comment here in youtube)
Don't forget to share this channel with your friends that might be interested in geoscientific topics.
:)
@@OneGeoscientist Sir, Thank you for the suggestions.
how to calculate depth of the water zone using VES Resistivity Survey
Thank you for your comment.
This is an easy question to ask but it is not simple to answer.
Detection of the depth to "groundwater level" is not possible in many cases because "resistivity contrast" and "resolution at depth" are not often sufficient to be able to affect recorded resistivity data. Thus, the groundwater level or thickness of water-saturated zone is often questionable or in best cases, tricky to find.
In addition, the violation of 1D assumption would be a severe problem in VES data analysis because it can occur in many cases in the field (despite the face that we presume the 1D assumption is correct). I suggest you to have a look at my paper (available in the link below) to read a relatively comprehensive discussion on this problem:
www.researchgate.net/publication/337027654_Assessing_the_effects_of_1D_assumption_violation_in_vertical_electrical_sounding_VES_data_processing_and_interpretation/citations
I hope it helps you.
Good Luck.
Pls give me a more elaboration of about the models &inversion processes. Tq u.
Hi
If you follow the ERT sessions from session 1 to session 5, you will get a nice idea about resistivity, inversion, etc.
Follow ERT playlist in this channel
ruclips.net/video/rHCbyuP-5tc/видео.html
🤩
Thank you Sir
If you liked our contents, share it with your friends.
Good Luck