How to use ERMs for treasure hunting?

[1843]

Hi all,

Could you give me an article about working with ERMs?
I don't know how to work with them...

Thanks in advance,
1843

[Tim Williams]

Are you talking about Earth Resistivity Meters?

[1843]

Yes, I am.

I want to know how can I use an ERM to detect an 1m x 1m area (from surface to 5m under the soil) ?

Would you please explain?

Best regards,
1843

[Leto]

resistivity mapping

Hi 1843,
I do not know what are you searching 5m underground?
Cave, buried treasure, lost building foundations, water, mineral deposits...??

OK let's say it's buried treasure chest
To place treasure chest 5m undergroud pirates had to dig very big pit-hole.
Hole was after filled again with soil normally more damp and humic relatively to surrounding undisturbed soil.
More damp also means less resistance to current..
Resistivity meters measure the those differences in electrical resistivity of soil.
Readings should be taken on a grid covering the whole site you think treasure is.
Results (varying resistances) should be then plotted acording to grid used on site.

Posted picture shows one such plotted result (40x40m) with feature resembling one bigger hole in one corner of linear features - ancient parcelization.

[Tim Williams]

Well 1843 that's a good question. First let me say that the ground is measured as resistance. A current source using two probes is set out on the ends. 2 more probes measure the voltage drop. Depending on the probes distance for a 4 probe system. X amount of current will pass through the soil and that voltage drop is measured.

But the readings are relative to the ground conditions! remember this! You see some systems with a meter on them that have gold and other metals. They even give you a resistor to test it with. In real life you would have to be at the same place under the same ground conditions for that meter to work! Don't be fooled. Ground resistivity is hard work.

But lets say we are looking for an object the size you say. You would have no problem locating it with ground resistivity unless, the ground conditions cover the target. If the target is sitting in water, the target will not show as good if it were not sitting in the water. Why? Because the current will take the short path from one pole to the other. If the target is metal the resistance reading will be lower than the rest of the ground. If the target is cement vault the resistance will be higher than the rest of the ground.

So don't think just because your meter is at the gold position you hit gold! I would think you hit water!

Let say you are looking for a cave. You start out with the probes 10 feet apart. Depth on my system is about half the distance of the probes. You take a number of readings and you see this data.

10ft = 300 depth 5ft
15ft = 310 depth 7.5ft
20ft = 1000 depth 10ft
25ft = 1230 depth 12ft
30ft = 1100 depth 15ft
35ft = 800 depth 17.5ft
40 = 350 depth 20ft

At 10ft depth you hit the cave and at 20ft you are under the cave. So the cave is 10ft area inside. On my site you can see the septic tank and drain field.

http://lrlman.com/Pages/GCG/gcg.htm

I have a 2 probe system. But my unit has digital filtering to increase resolution. It can be used alone with a dc meter or with either logger to get the plots you see on my site.

I hope I answered your question. Ground resistivity measures the difference in the ground from one area to the next by the path between probes.

[1843]

Thanks for the info.

There are some way for the probes arrange.But I don't know which one is better for tresure hunting.
My desired target is about 20cm x 20cm, and I don't know how deep it is.(1m...5m)
- Is twin-probe the best choice?
- What distance should be between the probes?(C2,P2)
_ What distance should be between the probes(C1,P1) and the matrix?

[1843]

Here is the my logger view:

[Tim Williams]

The arrangement you are using is a good one, but is good for around the distance of the twin probe setup you are moving through the grid. So if the distance is 3 ft then you are seeing down to about 2.5ft in depth. If you are to see deeper you would have to widen the probes.

[Tim Williams]

Can you send me the data from your logger my software will show more detail if I can convert it.

[1843]

Here is the data:
earthres 1.txt

[Tim Williams]

Wow thats some data. Does your software have an export option? If so export the data in xyz format. If not tell me what was the grid size of the data file you sent.

Tim

[rael]

Hi,

For export the EPE RM data in xyz format, look this:

Earth Resistivity Meter thread.
http://thunting.com/geotech/forums/s...ad.php?t=12521
http://thunting.com/geotech/forums/a...4&d=1172869384

Rael

[1843]

Wow thats some data. Does your software have an export option? If so export the data in xyz format. If not tell me what was the grid size of the data file you sent.

Tim

I don't think if it has...I don't know about grids etc.
It was an example in its software folder.

[Tim Williams]

Look here for some testing on different systems and methods.

http://lrlman.com/yabb/YaBB.pl?num=1192931144

Tim

[1843]

Thanks for the link.

Could you explain about the pole-pole array?