Detecting Caves and Voids

[wam]

This is how we did it

She was insisting that it is a fish - I said that it's ceramic pipe only.
Then she moved sensor about meter away and the sensor is showing only noise. I went to work but she decided to do some digging just in case it is a fish.
It is not easy to have dispute with ladies.
Wam

[wam]

Fish finder problem

Hi, looks like no one get exited about my cavity Fish Finder
idea. But may be some one can advice some tip how to open
fish finder box. I have intension to replace broken glass but how to open
the box? Right now I am prepared to cut it all around.

[bulsack]

Don't let it bother you. just put clear scotch tape over the crack to keep moisture out. Did you try you'r scheme at another location?

[Ganesh]

poor mans eye into the earth

Hi, looks like no one get exited about my cavity Fish Finder
idea.

Hallo Wam,
I think in order to get excited about it you need to do some more experiments. How does your fishfinder react if you bury a heap of Newspapers in the ground? Better would be a heap of dollarbills but I guess you don`t have a big enough bundle to bury to be detected from the fishfinder??!.
Who knows may be you've found the poor mans earth cache detector.

A few experiments in the backyard should make it clear if that is a sort of toy gimmick or if it could be used to detect abnormalities in the ground.

Thanks for the funny presentation with the Kitty.
Ganesh

[Funfinder]

@Geo
If you have the chance you could go to Istanbul for testing the Makrodedektör Jeohunter but I guess it's the same like with the Gemini III - detecting caves is the "same" like hot rocks, ceramic or mineralized stones.

I haven't tested it so far if a cave or hole has a stronger signal-value as minerals etc. If so, you could adjust the GEB at mineral level so caves only get detected.

Anyway - with my Jeohunter I would recognise if it's a tomb or cave simple because of the detection-signal size.

As already tested very large metal objects and so caves would get detected minimum to 3-4m depth.

With correct ground balance a "rectangular cave" of 1x2m will get detected until around 2,5m depth and the shape would tell me that it's no mineralic stones or bricks etc. But I wouldn't dig that deep anyway!

OK - maybe yes - but only if there's plenty of gold in there...

[Tim Williams]

Here's a plot showing a void and another a pipe. Both were done with the tm-808 in cave mode-auto. Of course these are not that deep but targets have been recovered to 14ft.

Tim

[mrkhrdr]

Elijah, & all,
Did you try digging?
Seriously, by the time you figure out how to build, buy and use any of these geophysical devices, you can have done an awful lot of serious digging and rock-moving to open up those sinkholes. There are some clues and safety concerns to doing this; but if you are looking for caves in order to enter them, you will have to do some digging anyway.
But if the journey itself is the goal and the journey must be geophysical, there are the options discussed above - gravimetry, conduction, and seismography. I can think of one more family of techniques that could be used, namely, electromagnetic pulse detection. One coil is pulsed and sends an EM wave through the rock. Other coils, strategically placed, pick up the direct pulses and their echos from any sharp transition in the impedance of bodies in the rock. These conductance anomalies can be either positive or negative - as an empty void would be. Software back-solves for the shape and location of the disturbing body. The idea is really not that different from seismography in that a bunch of waves are recorded and the source of any anomalies is computed.

[dcyoung9]

Rocky or sandy is good for GPR, as long as the conductivity of the ground is not high. For instance, here in the Northern part of Sweden one can easily penetrate down to 25 - 30meters. That's because it's mostly rocky/sandy with a very low conductivity. I have tried the same antenna in the suburbs of Paris and I hardly get 10 meters! The point is that you should check the conductivity of the ground before you rule out GPR. Sure, it doesn't work everywhere, but where it does it is unbeatable by speed of survey and the quality and clarity of the results.
I found out that where GPR has a poor performance, resistivity is a better choice. But, at the same time I know that archaeologists prefer magnetometers for doing basically the same job.
I cannot tell anything about OKM, except for the fact that it is not a GPR in the common sense of that word, but I cannot tell you that it doesn't work in your particular case without knowing more details.
Hope this helps.
RA

I have a Cesium vapor magnetometer...
Will someone please tell me how you find a void with a magnetometer?
I can find a freshly dug hole but not a hole that is old.

[kamel]

Hi all

For me the best method for detecting and characterizing the caves and voids, is the Electrical Resistivity Tomography ERT method, of course too the GPR tool is good too, but if you use the ERT make sure the the best array for detecting and the best spacing inter-electrode. there are many papers include the detection of caves, around the world.

Kind regards
Kamel

[mrkhrdr]

Thanks.

Hi all

For me the best method for detecting and characterizing the caves and voids, is the Electrical Resistivity Tomography ERT method, of course too the GPR tool is good too, but if you use the ERT make sure the the best array for detecting and the best spacing inter-electrode. there are many papers include the detection of caves, around the world.

Kind regards
Kamel

That was a very helpful reply.