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Archaeology Resistivity

Posted: Mon Mar 15, 2021 8:59 pm
by Relic
To kick this year off I managed to convince an archaeologist that I wasn't only interested in Coronado's lost hidden secret gold stash. So, in addition to providing a conductivity survey I agreed to investigate closing out a resistivity data set. I've never seen this type of resistivity and I'm unable to locate a unit with a mini array on a boom like the one in the photo. I'm wondering if my mini sting can be rigged to do this? I just have a half acre to do.
gc_2009_remote_sensing_GP.jpg

Re: Archaeology Resistivity

Posted: Sun Mar 21, 2021 9:55 am
by geophix
It looks like there are only two probes in the photo. So it measures voltage and injects the current at the same pair of probes? I remember I did use one of current probes for both current injection and voltage measurement for one of my surveys using SuperSting. What I did was to "short" the two probes together. For example, in the command file I use probe 1 and 2 for current injection, and probe 3 and 4 for voltage measurement. Then I connected ("shorted") 1 and 3 using a cable (probe 3 is not connected to the ground). So effectively it injected current at probe 1 and 2, and measured potential between 1 and 4. I did get good results for the purpose of the survey. I am not sure whether it's going to work if you also connects probe 2 and 4 in this example.

Re: Archaeology Resistivity

Posted: Fri Mar 26, 2021 10:46 am
by Relic
Thanks geophix. I probably should have searched up a four electrode unit for a picture although I do think the one pictured has four very closely spaced electrodes. The info I've found is pretty vague and for a while I was skeptical about these things delivering legit data. I believe its just the Arkie community that uses these instruments so there are very few units out there and they are territorially guarded with no chance for finding a rental.

I'm gonna rig up my MiniSting and just try taking some data. This may end badly! Like my smoking corpse desperately clutching my latest creation while EMS pokes at me with sticks wondering if it's safe to approach. I hate to say it but I may need a beer to gather the courage to press that "Collect Data" button.

Re: Archaeology Resistivity

Posted: Fri Mar 26, 2021 2:21 pm
by geophix
Keep the current low so you have less risk of damaging the unit.

Re: Archaeology Resistivity

Posted: Thu Apr 01, 2021 12:32 am
by 99thpercentile
The most common resistivity array used for archaeology is the twin array, which is most likely what that system uses. It is very similar to a pole-pole array with one current and one voltage electrode on the movable frame. The other two electrodes are at infinity (~30 times the movable electrode spacing). The two fixed electrodes are usually the same spacing as moveable electrodes. Since the fixed electrodes are so close instead of on opposite sides of the grid, it isn’t really a pole-pole array.

You could use your SuperSting, but the logistics would be a pain. I bought a cheap four electrode resistivity meter off of eBay for about $300 that does these surveys quite well. The only drawback is that you will need to write down the numbers. You can also do the same thing with two multimeters and a sealed lead acid battery. I built a frame like the one in the picture with lots of holes so that I can change the number of electrodes and spacing.

The instrument in the picture is probably from Geoscan Research in the UK and retails for about $15K.

Re: Archaeology Resistivity

Posted: Thu Apr 01, 2021 11:26 pm
by Relic
Wow. I'll be hitting up Ebay real soon. I was just getting started with digging up this answer and wasn't getting any real answers. "The unit consists of a square electrical box on a frame with probes that are stuck into the ground". I owe you a beer. Do you think there is any chance of datalogging with an Arduino?

OK just went to Ebay. I owe you a 6 pack of freshly canned Crank Yanker IPAs (i have connections).

ETCR3000B Digital Earth Resistance Soil Resistivity Tester Meter 1PCS.... $470 That just ain't a geophysics price.

It will log 300 readings and seems to have some sort of interface. This could be my first piece of gear that doesn't interface via XP.