Movement/Vibration Detection Pt.2

I didn't see the last thread, but I'll chip in.

That depends on your signal source and other noise sources. I used to work for a Geophysical company that made big "thumper" trucks among Geophones and Seismic systems:

These systems are easily good for tens of km.

I routinely did testing in which is was easy to pick up passing trains and trucks a few km away etc. We often had to test in the dead of night to get a clean enough noise floor. And this was often *with* specially designed dampened attenuator rigs.

Yes, it's routinely done in large oil exploration and other geological surveys.

They should easily pick up those noises, but won't be able to "account" for them or cancel them out unless you are able to use some sort of post processing. Basic analog filtering is probably not an option unless you know all the variables involved.

Yes, that would be possible. You'd need say a custom A-D system and micro to process the signal and send an SMS or whatever by an off-the- shelf module.

Software for this kind of thing is many and varied. Most of it is custom.

Complex post processing of this sort of stuff though often requires

*massise* computational power. Seismic processing has been (and still is) one of the major uses for Cray and other Supercomputers. Taking data from a 3D (or even 2D) array of geophones and pinpointing stuff is a science in itself.

Dave.

The signal at one frequency falls off sort of like:

Y =3D A*(1/X) * exp(B*X) + C*(1/X^2) * exp(D*X)

Part of the energy travels as a surface wave and part of it goes through the body of the ground. In the body of the ground, there is compression and shear waves. This means that there are really three sections to the equation. The part in the soil has reflection and refraction acting on it. The energy can either be bent down into the soil and thus not get to the geophone or bent up and towards the geophone.

I guess this is a long form of "it depends". A geophone can also see things like the wind blowing the leaves in the trees.

Yes.

********* I am also going to send an email to someone who knows a lot more about this than I do. I may have better answers a little later. *********

If there is software, somebody did the programming. There is a lot of preexisting code that does a lot of stuff. Finding the right stuff can be a bit of a project.

On Jan 20, 9:42=A0pm, "David L. Jones" wrote: [... good stuff..]

There is a trick that has been used for years where you wire geophones in series and parallel. The desired signals add and the unwanted tend to cancel. This is one of those talents that old crusty prospectors have. It isn't really a science.

Thats cool, he could bring the leads out to a switch panel and use toggle switches to reverse phases of the pairs. Sort of like a directional antenna array.

Or as another thought, How about a central array of 4 geophones and a switching scheme like used in a doppler radio direction finder (check ham radio construction articles) to induce a phase signal for processing to a display to provide direction.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Use only Genuine Interocitor Parts" Tom Servo  ;-P

d

Beamforming is a similar technique. It needs a lot of processing power.

Leon