Truly informative and useful explanation. Thank you. I have a question dear David. As far as I know, electrical resistivity measurements are ideally applicable where there are relatively negligible subsurface variations both horizontally and vertically. however such an ideal situation is in fact unattainable. How much deviation from this ideal condition can be allowed? what about non-homogeneous conditions? Can we trust the result for example on the basin slopes (basin edges) where the horizontal layering between electrodes can be violated? Many thanks.
Thank you Christos. It was a casual lecture oven to Geography students on a cold wet day in the north of England, on the surface of a major landslide site at a place called Mam Tor.
Hi Juzer. I'm the guy in the video - lecturer in Forensic and Geographical disciplines at LJMU, Liverpool, England. Giuseppe is correct - specifically it is the Syscal Pro 72 - which means it has up to 72 electrodes available. It is my very favourite piece of equipment. I hope you have the chance to benefit from this wonderful, exciting area of science.
This demo could have been done more easily in the University campus grounds! The explanation should be done beforehand and the practical aspects of electrode placement and connections etc. shown on site.
@@karhukivi I bow to your superior knowledge. Perhaps you might, however, ask yourself whether, perhaps, I do in fact teach these subjects in the university campus grounds and whether there might have been a specific reason why, on thus occasion, I was teaching such basic matters on a hillside in the north of England. Just a thought.
@@Brynmawrhill I know you do! but I did wonder why those students had to stand and listen in the cold. They should already know the basics and be able to lay out the cables and make the measurements before they get to a real-world application. A close-up of the equipment and a diagram of the geological situation would have been interesting, next video perhaps?
@@karhukivi Why "should" they? You do not know who they are, what they were studying and why they were at this particular location on that particular day.
@@karhukivi So tell me why I was teaching these specific students on that specific location on that specific day. It seems a little silly to criticise something the circumstances of which you have no idea.
No. Resistance is the more correct term because we measure the ratio of current to potential to calculate resistance but we then infer resistivity with reference to the electrode geometry. The value we measure can be exactly interpreted as resistance (or, indeed, impedance, though these are usually DC measurements) but the inferred resistivity value is only ever an approximation which requires certain assumptions. This is why we refer to it as 'apparent' resistivity.
@@Brynmawrhill It is not resistance that is measured. However, the units of voltage divided by current (V/I) appear in units of resistance. In fact, four electrodes are required to exclude the contact resistance of the electrodes, so the current is passed through one pair of electrodes while the potential difference is measured between another pair. The appropriate geometrical factor for the array used converts this to apparent resistivity, the word "apparent" implies that ground is assumed to be isotropic and homogenous for the purposes of the calculation.
@@karhukivi You make my point well. Resistance - the ratio of voltage to current - between the four electrodes is what we actually measure. Resistivity - whether accurately known or apparent - is always based on assumptions of homogeneity in the subsurface which we can pretty much guarantee do not hold. The inhomogeneities are, after all, what we are seeking to reveal.
@@Brynmawrhill I think you are missing the point it is not resistance, although it has the units of resistance, ohms. The values of "resistance" obtained in a multi-electrode array bear no relationship to the inter-electrode resistance nor the contact resistance of the electrodes with the soil. An analogous example would be hydraulic conductivity which has units of m/s which looks like velocity but is not. The flow velocity also depends on porosity and hydraulic gradient. Aquifer transmissivity is even stranger, with units of m²/day which looks like the output of a carpet factory! Apparent resistivity can even have negative values, especially in down-hole surveys, but resistance cannot be negative. The multi-electrode survey in the video is correctly known as "electrical resistivity tomography", the name used by manufacturers and practitioners in their publications.
Hi Ikenna, I'm sorry I didn't see your request sooner. Yes, you can contact me by Skype. Please find me at LJMU, Liverpool online (just search for David Jordan LJMU) so you can see a bit more about me. Where do you live and work? 2hat is your interest and application for ERT? Greetings from Liverpool, David
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How useful is this method/technology for archeology, specifically for searching for voids and tunnels?
That girl is feeling soo cold 😄
I live in Karachi Pakistan and I like your comment
Yes. It was a cold day! I was warm because I was running around the hillside teaching. 😁
Truly informative and useful explanation. Thank you.
I have a question dear David. As far as I know, electrical resistivity measurements are ideally applicable where there are relatively negligible subsurface variations both horizontally and vertically. however such an ideal situation is in fact unattainable. How much deviation from this ideal condition can be allowed? what about non-homogeneous conditions? Can we trust the result for example on the basin slopes (basin edges) where the horizontal layering between electrodes can be violated?
Many thanks.
I live in Karachi Pakistan and I like your comment send 10 month ago
Scioscope in Germany is known for EIT equipment.
Useful demonstration!!!
Chris Kyle
Thank you Christos.
It was a casual lecture oven to Geography students on a cold wet day in the north of England, on the surface of a major landslide site at a place called Mam Tor.
wanna know which university or institute its?
which equipment is it , thankyou
It is a Syscal Po (IRIS Instruments Inc.) equipment
Hi Juzer. I'm the guy in the video - lecturer in Forensic and Geographical disciplines at LJMU, Liverpool, England. Giuseppe is correct - specifically it is the Syscal Pro 72 - which means it has up to 72 electrodes available.
It is my very favourite piece of equipment.
I hope you have the chance to benefit from this wonderful, exciting area of science.
..
@@gabberson I live in Karachi Pakistan and I like your comment send 10 month ago
Strategies for locate well location in flat terrains with no significant morphological features??? Exlpian???
...
.
dGPS is my usual solution to locating each electrode in complex terrain.
I see that they're using Iris instrument.. is it better that ABEM?
Both are good.
I live in Karachi Pakistan and I like your comment if you don't mind
@@narendrasharma8681 Chris Kyle
What’s the device called? Who makes it?
/
A Syscal ProSwitch 72 made by Iris instruments.
This demo could have been done more easily in the University campus grounds! The explanation should be done beforehand and the practical aspects of electrode placement and connections etc. shown on site.
@@karhukivi I bow to your superior knowledge. Perhaps you might, however, ask yourself whether, perhaps, I do in fact teach these subjects in the university campus grounds and whether there might have been a specific reason why, on thus occasion, I was teaching such basic matters on a hillside in the north of England.
Just a thought.
@@Brynmawrhill I know you do! but I did wonder why those students had to stand and listen in the cold. They should already know the basics and be able to lay out the cables and make the measurements before they get to a real-world application. A close-up of the equipment and a diagram of the geological situation would have been interesting, next video perhaps?
@@karhukivi Why "should" they? You do not know who they are, what they were studying and why they were at this particular location on that particular day.
@@Brynmawrhill I know something about teaching geophysics to students.
@@karhukivi So tell me why I was teaching these specific students on that specific location on that specific day. It seems a little silly to criticise something the circumstances of which you have no idea.
i love it man
😊😊😊😊😊😊🎉
Please how do U correct for topography in this Electrical Tomography?
I use the software Res2DInv - the full version, which makes it possible to introduce topographic values for correction.
I live in Karachi Pakistan and I like your comment send 10 month old
@@Brynmawrhill Chris Kyle
The body language of the women standing in front of him is complete boredom and disinterest.
Electrical resistivity not resistance like in title
Chris Kyle
No.
Resistance is the more correct term because we measure the ratio of current to potential to calculate resistance but we then infer resistivity with reference to the electrode geometry.
The value we measure can be exactly interpreted as resistance (or, indeed, impedance, though these are usually DC measurements) but the inferred resistivity value is only ever an approximation which requires certain assumptions. This is why we refer to it as 'apparent' resistivity.
@@Brynmawrhill It is not resistance that is measured. However, the units of voltage divided by current (V/I) appear in units of resistance. In fact, four electrodes are required to exclude the contact resistance of the electrodes, so the current is passed through one pair of electrodes while the potential difference is measured between another pair. The appropriate geometrical factor for the array used converts this to apparent resistivity, the word "apparent" implies that ground is assumed to be isotropic and homogenous for the purposes of the calculation.
@@karhukivi You make my point well. Resistance - the ratio of voltage to current - between the four electrodes is what we actually measure. Resistivity - whether accurately known or apparent - is always based on assumptions of homogeneity in the subsurface which we can pretty much guarantee do not hold. The inhomogeneities are, after all, what we are seeking to reveal.
@@Brynmawrhill I think you are missing the point it is not resistance, although it has the units of resistance, ohms. The values of "resistance" obtained in a multi-electrode array bear no relationship to the inter-electrode resistance nor the contact resistance of the electrodes with the soil.
An analogous example would be hydraulic conductivity which has units of m/s which looks like velocity but is not. The flow velocity also depends on porosity and hydraulic gradient. Aquifer transmissivity is even stranger, with units of m²/day which looks like the output of a carpet factory!
Apparent resistivity can even have negative values, especially in down-hole surveys, but resistance cannot be negative. The multi-electrode survey in the video is correctly known as "electrical resistivity tomography", the name used by manufacturers and practitioners in their publications.
Very nice explanation. I will like some bits of explanation please. Let me know I can I contact you through Skype please. Thanks
Hi Ikenna, I'm sorry I didn't see your request sooner. Yes, you can contact me by Skype. Please find me at LJMU, Liverpool online (just search for David Jordan LJMU) so you can see a bit more about me. Where do you live and work? 2hat is your interest and application for ERT? Greetings from Liverpool, David
I live in Karachi Pakistan and I like your comment