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Author Topic: REQ: in search of GPR Ground Penetrating Radar  (Read 1384 times)
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sphinx
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« on: November 02, 2010, 12:45:42 12:45 »

hi all

i am in search of a radar said above nothing really fancy but something simple like a project to be able to in a simple
way to read the ground a bit like resistivity metering just would be funny to be ablt to see underground structures.
like walking over an area with the apparatus the put reading in a computer and the try to read the values out of that
and make a assumption of what that could mean.

does anyone have any ideas on that, i have searched but not found anything good like schematics or any other good
info. any help is appreciated

best regards
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« Reply #1 on: November 02, 2010, 04:35:18 16:35 »

Hi
There is some information on building a GPR here
http://www.geotech1.com/forums/showthread.php?t=11772
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2N5109
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« Reply #2 on: November 07, 2010, 01:42:04 01:42 »

The most commonly transmitted GPR waveform consists of a single cycle of RF, much like the waveform of a UWB (ultrawideband) signal.  (Indeed much of the development of UWB radars follwed GPR as higher frequency power sources became available.)  A single cycle of RF has energy content over a wide bandwidth, over an octave, so the concept of "frequency" has less meaning, and GPR systems are designed in the time domain. 

The frequency of the single cycle of RF can be chosen roughly as follows:

Depth     Frequency
0.5m      2400MHz
1.0m      900MHz
10.0m     200MHz
20.0m     50MHz

The component design boils down to building a bistatic radar:   

1.  a signal generator which can synthesize a single cycle of RF
2.  an antenna which can radiate that spectrum into the ground
3.  a receiving antenna or array, spaced some known distance from the transmitter
4.  a set of receivers attached to the receiving antennas
5.  recording and signal processing means to correlate received returns with known targets and locations. 

When you look at the problem this way it becomes a little more tractable and you can specify and design components based on desired performance and physical limitations.  If there is interest this can be continued. 

--2N5109
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sphinx
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« Reply #3 on: November 07, 2010, 08:47:59 08:47 »

ok i am beginning to undestand now how the radar works in big, i was searcing the net for any designs but could not find any, i also figured out the the higher the Hz is the smaller the subjects you can see underground or should i say anywhere my guess is that a  radar wherever it is used for it works in the same way. so maybe some sort of "normal" radar can also point me on how to build it (this is what i think might work)

for the depth i would be more than happy with 0.5-1m at maximum o 2.5m over that for experiment purposes is of no use for me

as long i would have something simple to expand for future needs, i would start with something simple i would know what to expand with when i get to learn more of what needs i would be looking for.

best regards
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2N5109
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« Reply #4 on: November 08, 2010, 03:43:29 03:43 »

The approach is to divide the GPR system into its component functional parts, and do a search for those parts, instead of searching for the system itself which did not turn up a lot of useful information.  That's why I listed those 5 things in my last post.  So taking number 1, the signal generator, there is a simple circuit you could build at:   

http://www.holmea.demon.co.uk/Avalanche/Avalanche.htm

It looks like a well written article and the circuit looks like it will work.  There are ways to speed up the pulse by adding step recovery diodes, optimizing the device type, etc., to get the spectrum into the GHz range.  This article is instructive also because he was building it for use as a Time Domain Reflectometer (TDR).  This shows the similarity between a TDR and ground penetrating radar.  The TDR includes a very fast scope to look at the reflections in the time domain.  In fact if you attach a TDR to an antenna matched to the ground, and look for reflections. you have about 90 percent of the GPR hardware built.   

--2N5109
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Parmin
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« Reply #5 on: November 08, 2010, 05:57:09 05:57 »

With apology to sphinx for sorta hijacking the topic...

Might not be the right forum here, but,

can anyone tell me if GPR was used in the mine drilling jobs?

such as the one they used to rescue the Chilean miner lately?
it was a very long distance drilling done there,
and something must have been used to measure the drilling direction.
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2N5109
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« Reply #6 on: November 09, 2010, 02:46:04 02:46 »

I don't think they used any GPR there because they knew roughly where the miners were with a test hole and there is no GPR that has a range of their depth of 300m through rock.  Speaking of accurate drilling, what amazes me is how the relief well for the blown Deepwater Horizon well was navigated.  To stay on topic and keep Marlon happy, a form of GPR well logging is used to determine location and hydrocarbon content around a well hole before it is cased. 

--2N5109
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