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Re: [Phys-l] Need advice to build earth resistivity meter

This is the method taught at NPS to detect beach mines. The thumper tho is something like a speaker and the michs are piezoelectrics, probably the same ones they use in the "water" acoustics labs.

bc, wondered what the heck the huge barrel of sand was doing in the basement swimming pools room, and suspects only a 1/4 in will soon be concave. A railroad tie plate will probably do. [3/4 " w/ ridges an addnl. 3/4] Still thinks it's a great doable idea.




Brian Whatcott wrote:

At 04:33 PM 9/18/2007, Roberto, you wrote:

Hello Friends:

One studient has the idea of building an earth resistivity meter capable of

cut

ed.

My best regards.
Roberto


Without any great insight into Earth resistance testing, I am going to
suppose that this method is not practical as proposed.
There is a practical method into which the student's interest might
be diverted. It's called hammer and plate seismics.

Briefly: a sheet of (say) 1/4 inch thick steel plate measuring perhaps
3 ft on a side, is placed on a terrain of interest.
Several microphones are stuck into the ground on two lines extending
from the plate in different directions. One microphone near the plate
is to act as a trigger for a multi pen recorder, or some computer-based
data acquisition equivalent.

A sledge-hammer is swung so as to impact near the center of the plate.
This is noisy! The echoes seen at various pens give some sense of
subterranean surfaces when the various path lengths are accounted for,
in favorable circumstances. Even so, I seem to recall it needs explosive
stimuli to visualize targets as deep as 1500 ft.

As a more speculative alternative, I seem to recall that sub-surface
radars are now depicting layers at respectable depths.
Such results for a particular location may even be available
from some agency like NASA for example.



Brian Whatcott Altus OK Eureka!
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