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PostPosted: Fri Aug 19, 2016 12:45 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
(Sorry for my english)

Hello, everyone. I'm a engineering intern, and my job is just to do some studies about GPR, and do some surveys.
Yesterday I was in a ducts field, and I used the GPR for the first time, but I couldn't see a thing. (These ducts are about 1.5m of depth, and 14').

I guess something is very wrong, cause my image is almost a constant of traces. I come here just to have your opnion. How can I correct this? What could I had do wrong? Please tell me something that I can be doing in a wrong way, so I can test it and post here the results from your help.


Setup
Antenna: GCB500
Distance mode;
Range (ns): 100ns;
position - offset (ns): 3ns;
traces/meter = 112 (profile 122,123 and 124) / 52 (profile 125);
Gain: 0 (Amount of gain points:2; Point 1: 0; Point 2: 0);
No background substracted;
Stacks: 256;
Filters: HP(MHz) - 250MHz / LP(MHz) - 1000MHz


I'm sending a image from Profile126.gsf, with a logarithmic gain (Point 1: 0; Point 2: 30dB), and the .gsf files without processing.

Thank you guys, so much.


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PostPosted: Sat Aug 20, 2016 3:28 pm 
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Joined: Mon Mar 16, 2015 7:26 pm
Posts: 14
hello,Klauscb

firstly, set the stack to the minimum value like( 0 or 3 traces) before collecting the data. I think the result will be changed .
convert the profiles to dzt extension and share them to help you about the processing .


with my best wishes


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PostPosted: Mon Aug 22, 2016 6:18 am 
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Joined: Tue Nov 30, 2010 3:21 pm
Posts: 30
hello Klauscb,
as geomouhamed suggested, you need to lower the stacking to a much lower value (3 is OK).
The next thing I would suggest is to lower the range to value around 40-50ns. If you are in an average type of a soil this would give you 2-2.5m of penetration and will not visually compress the information from the area you are interested in as much as what you have now.
I hope that these few changes will provide you with a better dataset that will be easier to interpret.
BR


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PostPosted: Mon Aug 22, 2016 8:10 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
Hi danne and geomouhamed

I did some tests with GPR (but in a place without ducts), but with just 1-3 stacks I was able to see some diferences in soil, and I really think that it was my mistake in the survey I told you.

I did some tests (here in company, that I'm intern) with 1, 2, 3, 10, 50, 100, 250, 500, 1000 and 2500 stacks to help me by seeing what really is changing with this parameter... and I'm able to clearly see the soil with 1, 2, 3, even 10 stacks... but more than this, my radargram is "outstretched".

So can you tell me why? Shouldn't stacks help me with Signal-noise ratio?


(Thank you.)


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PostPosted: Mon Aug 22, 2016 8:11 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
By the way, I'll do some new tests in the same place, with ducts. And I can post here the new results, if you wanna to see the difference.


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PostPosted: Tue Aug 30, 2016 11:49 am 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
Hi, I'm back.

I went back to the same ducts field, and now I have some new data. I'd set stacks to just 1. And for sure I have better results. But, how can I get even better results? I feel like it's not the better data aquisition that I can make with GPR. Maybe I'm wanting too much for my GPR, but I just wanna to make sure that I'm doing the best that I can.


Setup
Antenna: GCB500
Distance mode;
Range (ns): 50ns;
position - offset (ns): 3ns;
traces/meter = 113;
Gain: 0 to profile139 and linear (Amount of gain points:2; Point 1: 0; Point 2: 35) to profile140;
No background substracted;
Stacks: 1;
Filters: HP(MHz) - 250MHz / LP(MHz) - 1000MHz

Profile139 and profile140 in attachment. like asked for geomouhamed, files in DZT extension.

Thank for any help, this really means a lot.


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PostPosted: Tue Aug 30, 2016 8:34 pm 
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Joined: Mon Mar 16, 2015 7:26 pm
Posts: 14
hello,Klauscb

firstly ,one profile is not enough if you want to detect any target, you must measure many parrallel profiles depending on the area. and also you can save the data as raw data (without any pre processing).
-As for the processing you can watch this video and related videos about how to process the GPR data by gpr softpro software.
https://www.youtube.com/watch?v=n2irE9YjKik

but the main processing steps are:

1-surface correction
2- dewow
3- dc removal
4-hp,lp filters(IIR)
5- gaining
6- velocity detection(hyperbola ,slope fitting) to detect dielectric constant.

- can you tell us about the subsurface layers in this area (water saturation , caly bed, dry sand)?

and also you should read about the GPR method and theory ,I have attached all photos of a processed profile No.140 ( the depth is not correct)to interpret it.


with my best wishes


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PostPosted: Wed Aug 31, 2016 5:38 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
Thank you again, geomouhamed

geomouhamed wrote:
firstly ,one profile is not enough if you want to detect any target, you must measure many parrallel profiles depending on the area. and also you can save the data as raw data (without any pre processing).

I must have more than one profile to have sure that there are no targets with no detection?

geomouhamed wrote:
- can you tell us about the subsurface layers in this area (water saturation , caly bed, dry sand)?

Sorry, I have some difficulties to tell it to you, because of my english haha, but I guess it's like loamy soil. I'm attaching a picture with a similar soil where I do the acquisition of data.

geomouhamed wrote:
you should read about the GPR method and theory

Actually, I have been reading a lot about GPR theory, but now that I'm catching some data, I'm thinking that the theory helps, but not enough. And I need to have some experience, and I feel that I can catch a little of others experience here in forum.


Thank you for the photos and your help.


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PostPosted: Thu Sep 01, 2016 11:47 am 
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Joined: Mon Mar 16, 2015 7:26 pm
Posts: 14
It is a pleasure Klauscb ,it will be a useful thing If you share at least 3 parallel profiles .sgy without gps data to detect the pipes and make 3d model .It is up to you.

With my best wishes


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PostPosted: Mon Sep 05, 2016 5:11 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
geomouhamed wrote:
it will be a useful thing If you share at least 3 parallel profiles .sgy without gps data to detect the pipes and make 3d model


How should be the distance between the profiles?

What's the difference between .gsf and .sgy?


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