Electroseismic testing. Need help filtering 60hz noise

[C]

Did a little looking for you
Looks like the signal could be in 170-900 Hz range.
What I found the amplitude is in the PC microphone range.
For this frequency range good sound recorders are better then scope.

So record a signal then process the signal with something like Audacity on a PC.

[jitter]

We have talked about an amp but no one has recommended one?  Seems most just make them but I figure of there are some premades on proto boards or something, that might be just as easy.  ?  Or are we talking much more than an op amp?

My daily work is in testing and calibrating a specific instrument that has to deal with the same challenges you are facing. Because of an NDA, I cannot divulge any details, but there is no harm in a global desciption that might point you in the right direction.

The instrument operates in the DC-1 MHz range and can supply and sink currents while measuring the response. It can function as a voltage or current source and generate any signal shape, and is fully under the control of a PC with proprietary software running it. It can also just "listen", like a scope or DMM.

The interesting part for you is its front end. It's a differential amplifier with two electrodes with an incredibly high input impedance. It's common mode rejection is very good, and I think that's what you should be looking at building/buying. Basically each electrode is buffered by a very high input impedance opamp (e.g. AD ADA4627) and the differential signal is amplified and filtered by a very low noise opamp (e.g. AD797).

I tested in a remote location with electrodes E-W.  I have no detectable 60hz noise.  Maybe some harmonics but all seem to be way up the range.  My primary noise is 18mV p-p at 1 cycle per uV so 1Mhz, which I thought was an odd frequency being in the middle of nothing but.....

Yes, but the scope itself will have multiple SMPS sections inside, maybe you're looking at a harmonic from them...

Can an RC filter take care of this problem pretty easy?  If I can trim some of the higher frequencies, I might be able to get somewhere. 

If it's coming from within? I don't know, I think you should experiment.

Perhaps Dave can chime in? I seem to remember him having been working in a similar field... albeit on oceans...

[KE5FX]

This all sounds extremely woo-ish.  Like any other form of dowsing, it probably only "works" because it's hard to prove that it doesn't.

Even if the technique works, it will yield signals in the nanovolt to microvolt range.  Your scope is useful in the millivolts to tens of volts range.  You are going to need lock-in detection with a repetitive stimulus signal if you're going to pick up anything at all, I suspect.  Talk to some physics profs and grad students about it, if possible, and be prepared to show peer-reviewed literature before they take you seriously.

[htassell]

Hi,

As a geophysicist I've had a good deal of experience with most geophysical methods. Up front, I would say that electrokinetic method - which you are discussing, whilst does work in some circumstances, is certainly not the most reliable nor effective techniques at detecting the presence of groundwater.

The principle of the technique is a little bit different from what you describe - the dipole array is not an antenna it is a pair of galvanic electrodes that are measuring a change in potential (voltage) in the ground as a result of the compressional wave from the seismic source (typically a sledgehammer) causing a disruption to a phenomena known as Streaming Potential. Streaming Potential is a phenomena whereby the flow of groundwater with dissolved ionic species in solution through certain geological formations causes localized charge distributions which in turn generates a measurable 'self-potential' or voltage.

The theory of eletrokinetic sounding techniques is that a sledgehammer or explosive source induces a displacement or movement of groundwater through the formation, with accompanying localized zones of charge build-up. If you stick your electrodes in the ground, you can measure a voltage or potential across this zone. This is a galvanic phenomena - you are not measuring a B-field or H-field. Equipment used to measure the phenomena is pretty similar to a multimeter - just a high input impedance AFE with an ADC. Typical potentials measured are in the 1 to 100's of mV.

The main problem is that the ability to generate a measurable electrokinetic voltage is highly dependent upon the geology, the chemistry of the groundwater and whether there is any net of movement of the groundwater naturally. These factors tend to be orders of magnitude higher in the potentials they generate than the EKS response someone can generate from the surface with a sledgehammer.

My advice in terms of trying to find groundwater would be to simply carry out a self potential survey - that is, just measure the self potential generated by groundwater movement naturally. The technique is simple and will give you an indication of where to look. Just stick one electrode in the ground and then with a roving electrode, measure voltage every x metres in an orthogonal grid. Then grid/contour the measurements into a map of self potential (it will be positive and negative). Where you have significant potential, this can provide an indication of the presence of water flow in the near surface.

Ultimately if you want to directly measure the insitu % water content of the earth, NMR or nuclear magnetic resonance surveys are the best approach (provided there is no significant abundance of magnetite in your geology). Vista Clara make some of the best NMR systems.

[dmills]

IIRC the proton NMR resonance in the earths magnetic field is usually about a kHz or so or so, depends on how far from the equator you are.

Personally I would hook the electrodes to a hifi amp via a highpass filter and listen.