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Topic: geophysics (Read 11080 times) previous topic - next topic


The accuracy usually stated in the GOS specs are the horizontal uncertainties, the vertical uncertainties are much higher.  You can get sub-meter vertical accuracy with additional GPS units and some pretty intense processing, but not with a signal GPS receiver.


This type of surveying does not require vertical accuracy. The 2d data can be easily draped over a typical topo survey.

The point is, though, that this kind of survey could also be set up to take interval readings for a grid without gps. We don't need to get bogged down with gps accuracy.


I too love to make geophysics equipment.  I hate to rain on your parade, but those of you
thinking of making a resistivity meter should search online for DY4300. You will find
a Chinese earth resistivity tester selling for about US$ 240 including shipping.
I have one and I like it.  For it to act like a geophysics resistivity meter, you operate it in
4-terminal mode, or "rho" mode. In "rho" mode, you enter the Wenner electrode spacing and it
computes apparent resistivity.  It stores the  data internally (for about 1000 readings), but
it does not transfer the data to a computer (oops).  You have to do that manually.
A person might contemplate getting under the hood and finding a way to extract the readings
electronically. Maybe in five years a new model will come out that will allow the readings to be downloaded.

I think the Arduino is good for making other geophysical equipment, for
example a two channel VLF receiver that would emulate a Geonics EM16 or
ABEM WADI. Our efforts might better be spent there.



Is anybody aware of existing open source project on this topic?

I'm keen to build or collaborate on something for amateur archeological discovery.


2nd  ERM  will have 26 probes set at 1 meter intervals  measurments taken at 1mtr  2 mtr 3 mtr 4mtr spacing, this will give depth slices hopefully. 
26 is a lot of inputs - would there be some way to switch between probes? A system of relays? An ADC on each probe that would make the value available via some protocol or other?

One possible design might be an arduino nano or something for each probe. Sounds like a lot - but a nano is 20 bucks and I'll bet that your probes cost way more than that. Communication would be ... not sure. 12c won't work over that distance. Maybe just a daisy-chain of serial connections ... problem is that timing is critical for what you are doing (or is it?). If timing is a thing, syncing the probes might be an issue.

Or do these probes already have some electronics at the end, and its a matter of working out how to politely ask them to hand over their data?

Another possible design is much lower tech. Just write a sketch which, when you press a button, dumps whatever it reads on its analog inputs (or just one of them) into an SD card. You load that data into excel and deal with it however you may. The problem of  working out what those voltages mean is deferred to other software.

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