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 Post subject: GPR Quarry surveys
PostPosted: Mon Jan 10, 2011 10:46 am 
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Joined: Wed Apr 29, 2009 5:52 am
Posts: 96
Location: Zagreb, Croatia
Hi all!
This is a conversation I had with Geoscanners team about the GPR Quarry surveys with a specific antenna set (SubEcho 40) tips'n'tricks so if anyone has something to add I would be thankfull. Also I hope someone else finds this interesting and helpfull.
My question
Quote:
we are about to do some quarry surveys (stone exploatation).
we would need to determine the tickness of the top homogenous/monolith layer of stone, the depth to/zones of rubbles in the stone, cracks and caverns in the homogeneous/monolith stone.
do you have some guidelines for setting up the SE40 anennas for the task (distance between antennas, antenna to ground height, filters, scan rate, samples, preferable mode =point-distance-time, expected "blind" zone)

The answer
Quote:
Hi Goran,
SE40 for this is too coarse, don't you have a SE70? But, OK, if you don't have a SE70 then please use bistatic mode by all means, you won't be able to separate the top reflections in monostatic mode. Place the antennas no less than 1.7 meters from one another, preferably a bit more if possible. Distance from the ground should be between 200 and 300mm for best results.
Use HP=40 and LP=180, the samples is depending on your range for more than 1000ns use 1024, for less 512 is OK. I prefer time mode with these antennas whenever it is possible to drive smoothly over the surface, if not then I'd use point mode. Carrying the antenna with a handle and walking while collecting is the best way to screw your data. In monostatic mode the blind zone of this antenna is roughly 35 - 50ns, in bistatic mode you get better results 15 - 25ns. If you are in time mode then use a 50kHz PRF and 12 - 15 scans/second to obtain best results, a stack of 16 to 25 is very beneficial in these kind of situations when you are searching for cracks and debris.
I hope this is of help.

BR

_________________
"If the only tool you have is a hammer, you will see every problem as a nail."


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 Post subject: Re: GPR Quarry surveys
PostPosted: Fri Nov 11, 2011 7:16 pm 
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Joined: Sun Oct 30, 2011 7:17 pm
Posts: 6
Hi Bekic!
I have no experience with SE-antennas. I show here some results with MALA 5O MhzRTA.
The processing is with some REFLEXW modules .
I use correlation algorithms, which sometimes give better visualization of the environment.
The results are confirmed by drilling .
I could test this methodology with data from the SE-antennas,if i have any. :idea:
v.v.


Attachments:
File comment: the examples
gpr mala50mhz examples.jpg
gpr mala50mhz examples.jpg [ 172.65 KiB | Viewed 9831 times ]
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 Post subject: Re: GPR Quarry surveys
PostPosted: Tue Nov 15, 2011 7:02 am 
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Joined: Wed Apr 29, 2009 5:52 am
Posts: 96
Location: Zagreb, Croatia
Dear vvgprlook,
thank you for the data you shared with all of us here at GPR forum.
In the meantime I changed the company I'm working with and the quarry survey was never done due to unrealistic customer demands (or should I say not understanding the GPR technology) - they wanted a layering information about the stone deposits with 2-5cm discrimination at 25 meter depth......
Thank you once more.
BR

_________________
"If the only tool you have is a hammer, you will see every problem as a nail."


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 Post subject: Re: GPR Quarry surveys
PostPosted: Mon Nov 21, 2011 7:04 am 
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Joined: Thu Nov 10, 2011 7:58 am
Posts: 4
Location: Ukraine
Dear vvgprlook,
Your work is very interesting. Can you tell more detail about the processing? Is it possible to place the raw data from MALA 5O Mhz RTA?
Thanks.


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 Post subject: Re: GPR Quarry surveys
PostPosted: Tue Nov 22, 2011 2:17 pm 
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Joined: Sun Oct 30, 2011 7:17 pm
Posts: 6
Hi Bekic,
Hi Valerа,

To Bekic :
Too bad that there is such misunderstanding of geo-radar method.
Centimeter depth resolution at 25 meters is really practically impossible requirement.

To Valera:
Thank you for the shown interest in the results of my work.
In the link are included a few examples with records from 50 Mhz MALA RTA .
http://www.box.com/s/d0utb9artc2vztmf5ckx
About the processing of raw data:
so that we can give a reliable interpretation, we must be able to visualize the raw data. We can use different "integral transforms", like migration, semblance or other correlation algorithms. As example, I show here the results of processing from BRE1 and BRE2 models (http://www.gprmax.org)
By the processing of data from 50mhz RTA I use more complex modules. The antenna is a linear object, so I use twice the main function 'integral transformation', in particular, semblance.
If you are interested I can send you other materials-presentation with more examples and a little theory.
Regards


Attachments:
bre1 and bre2 examples.pdf [158.57 KiB]
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 Post subject: Re: GPR Quarry surveys
PostPosted: Thu Nov 24, 2011 9:04 pm 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi vvgprlook,
I've used spectral whitening in the past without much results.
Now, I saw you used also, it seems to be the last scan at the bottom of the PDF right?
If so, have you use it with real data? Have you got any results that otherwise would be difficult to get without it?
In the second scan from the bottom you used semblance as an interpretation method. Have you use this one with
real data? If so, have you perform some other processing before that or you applied to the "raw" data?
It is interesting because the first, second and third voids in the simulation should produce constructive wave addition
while the last one should produce a destructive addition. The processing shows the first, third and fourth to be better
presented. Is this an artifact of the simulation engine or it is the way is suppose to work?
The first two scans correspond, as far as I can see, to the BRE example 1. It is interesting that it misses the 75mm
object through the 200mm spaced objects but still can see a 100mm through objects spaced at 100mm. What kind
of processing did you use there?
All in all, very interesting, thank you very much for sharing.
Regards,

_________________
Reinaldo Alvarez Cabrera
Geoscanners AB
Sweden
http://www.geoscanners.com


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 Post subject: Re: GPR Quarry surveys
PostPosted: Sun Dec 04, 2011 7:56 pm 
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Joined: Sun Oct 30, 2011 7:17 pm
Posts: 6
Dear Admin,
I am very pleased that the processing that I use hier, is of interest to you.
The data from bre-models are "raw", as derived from the program GPR-MAX. The processing steps are described in the attachment.
Such algorithms are used with real data, as shown in the other attachment. The main one is in the use of “Semblance”
From the link http://www.box.com/s/d0utb9artc2vztmf5ckx
you can download the raw data of bre- models.

I am convinced that in the recorded raw data is recorded information about the structure of objects. Of course, this assumption must be confirmed by theory and practice.
An excellent example of the theory is the article’ A Simple Theory for Seismic Diffractions’, Trorey A.W. Geophysics No.5, 762-764, 1970.
The following example, which gives the relationship between theory and practice is
the processing of bre-models that I present here.

Finally, the processing of the real data:
The records with 800 MHz antenna are site study in the chemical industry.
We see areas in poor and good condition.We see underground communications.

The example with antenna 250 Mhz shows archaeological sites, ruins from the Roman Empire, before excavations. Here we see too the underground communications.

The last examples with antennas 100 and 50 Mhz are from geological studies.
I think that can be easily interpreted.

Finally, as my opinion on the discussion in this forum about GPR-certification of studies. I think, the post-processing with appropriate software is required. However, in field survey work is recommended to have software for rapid ‘in-field’ processing, which gives a similar display of objects-structure.This will make field work more efficient.
I will be happy if I was helpful.
Regards,
V.V.


Attachments:
gpr realdata examples.pdf [750.43 KiB]
Downloaded 530 times
bre-models-the solution.pdf [532.78 KiB]
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