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PostPosted: Mon May 17, 2010 6:33 am 
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Location: Boden, Sweden
Hi Hendraparley,
I downloaded your data and unfortunately there isn't much I can do about. There are many things that I don't have control over:
1. The vertical scale is in milliseconds which will render useless the hyperbola fitting routine directly.
2. The conversion from jpeg to sgy didn't go particularly well and the data is full of spikes.
3. The horizontal scale is corrupted since the converter picked up the default 1scan/meter which is unreal considering this is
a fiber optic cable not a oil tanker buried under ice.
This is regarding the data, but there are other things one needs to consider before applying the automatic tools of any software, GPRSoft, Reflexw, Radan, etc
it doesn't matter. Let's see, the distance is in meters which is very good, but, is it accurate enough? From the picture you posted I can see the hyperbola
occupies approximately 30cm in width at roughly 0.4 meters depth. With this data I'd assume you have a quite large fiber optics cable, but how large can
it actually be? Next, the zero position or surface has been already fixed, but I can see reflections over the zero point, the two distinct dark areas over
what was supposed to be zero. What are those? The EZ Locator has a shielded antenna and therefore these kind of reflections from the top should not be
there, right? But, they are and that means trouble when trying to use the automatic tools that assume the zero is the surface. Finally, the vertical scale is
in meters or depth if you wish indicating that you have calibrated the unit and found out the correct dielectric constant of this media, is that correct?

Regarding GPRSoft, all the scales are fully customizable, the vertical scales, left and right, can be independently customized to show depth or time. You do
that by going into the scales menu and selecting the type of scale you wish or even disable it if necessary.

You can watch a tutorial on hyperbola fitting with GPRSoft PRO here:
http://www.geoscanners.com/videos/hypfi ... itting.htm

Please send me an PM to discuss upgrading your hardware.
My very best regards,

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Geoscanners AB
Sweden
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PostPosted: Mon May 17, 2010 7:29 am 
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Joined: Wed Feb 17, 2010 4:56 am
Posts: 18
Location: Jakarta, Indonesia
GeoAdmin wrote:
Hi Hendraparley,
I downloaded your data and unfortunately there isn't much I can do about. There are many things that I don't have control over:
1. The vertical scale is in milliseconds which will render useless the hyperbola fitting routine directly.


actually the vertical scale is in milimeter, and that problem I can't solve until now.

Quote:
Finally, the vertical scale is
in meters or depth if you wish indicating that you have calibrated the unit and found out the correct dielectric constant of this media, is that correct?


It's true, but sometimes I want to know how to find correct dielectric using GPR Software

Quote:
Please send me an PM to discuss upgrading your hardware.
My very best regards,


Thx, oke I will send PM to you to discuss more ......

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PostPosted: Wed May 19, 2010 8:01 am 
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Joined: Wed Feb 17, 2010 4:56 am
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Location: Jakarta, Indonesia
Hi again Reinaldo

I want ask u again about this multiple. In here I have a radargram which show an anomaly, but in here can u show me the real hyperbola that show the object. Because from the information that I got from the worker that installed the pipe, they said that the pipe burried in depth around 80 - 100 cm, but the first hyperbola that I can see in radragram appear in depth around 0.4 m (40 cm). So, why that happened?. In here I attached the data

Best Regards

Taufik


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PostPosted: Wed May 19, 2010 10:22 am 
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Location: Boden, Sweden
Hi Taufik,
The ringing in the top of the radargram is too strong to let you see something clearly.
why don't you run a background removal first to get a better picture of what's going on?
As you have it right now it is very difficult to come to any conclusion.
Did you asked the worker the approximate diameter of the pipe you are looking for?
Another thing, it looks very suspicious the multiple reflections you have there.
Usually this kind of stuff are the result of a very shallow metal object. The kind of
pipes they use, at least here in Sweden, for protecting the communications wires are
made of plastic. A metal pipe will produce usually nice hyperbolas, please see attached
picture ("metalrör" = metal pipe).
My best regards,


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Geoscanners AB
Sweden
http://www.geoscanners.com


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PostPosted: Thu May 20, 2010 1:55 am 
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Location: Jakarta, Indonesia
GeoAdmin wrote:
Hi Taufik,
The ringing in the top of the radargram is too strong to let you see something clearly.
why don't you run a background removal first to get a better picture of what's going on?
As you have it right now it is very difficult to come to any conclusion.
Did you asked the worker the approximate diameter of the pipe you are looking for?
Another thing, it looks very suspicious the multiple reflections you have there.
Usually this kind of stuff are the result of a very shallow metal object. The kind of
pipes they use, at least here in Sweden, for protecting the communications wires are
made of plastic. A metal pipe will produce usually nice hyperbolas, please see attached
picture ("metalrör" = metal pipe).
My best regards,


When I'm doing survey for the first time, I usually found this case. The anomaly appear about almost from the ground surface (for the first time we think like u too, that anomaly coming from shallow object, near the ground surface), as you said it, Reinaldo. But, I think is not showing that anomaly is near the ground surface, because when we check it, the anomaly (ex : pipe) burried in depth around 70 - 100 cm. So, why this phenomena can happen? There are underground condition that make this phenomena happen (maybe : high conductivity or something else?).

Best Regards


Taufik

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PostPosted: Thu May 20, 2010 6:45 pm 
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Location: Zagreb, Croatia
Hi hendraparley!
I think that you are wandering about how to know the proper dielectric value at the time you are making a survey so you can perhaps make some of the conclusions about the depth of the anomalies even before you do any postprocessing - read the depths from the screen.
This is a from the trenches advice so test it for your self and see how it works for you before doing a payed job.
First of all: you cannot know the exact proper dielectric value on the field! There are some ways of finding out the exact value, but usually they consist of burring a metalic object on a known depth into the soil at question and going over to calculate the dielectric or putting electrodes into the ground and measuring the values of volts and amperes flowing among those electrodes. These methodes are usually not practicaly usable (how am I supposed to burry a metal thing below asphalt or concrete layer without destroying it escapes my mind totally :D ).
But....
The more and more surveys/tests you make you'll learn the possible values for the type of ground you work on (in Croatia I know that when on concrete I can set it to 9 and wouldn't be much off, cause the values I found after postprocessing where always 8-10,5) and it will give you a good guess of the dielectric to use and therefore the depth (in your case the workers said it is 80-100cm but you obviously placed a wrong value- the proper value now seems to be (1/2*sqrroot(the value you used))squared - after doing a few jobs on this kind of soil you'll know the approximate value by heart).
By now you are not satisfied with the answer I gave you! Obviously you want to know what to do till you get enough experience ?
Honestly, there is not much you can do about it, but you could try and use this table, I found it to be a great help/Guide for the possible values when started with the GPR 3 years ago:
Attachment:
soiltable.pdf

Everything else Reinaldo is suggesting considering the migration is valid (go figure :lol: ). Before doing it try to do all of the "cleaning" of the record - my usual flow of work is: zero positioning - IIR/FIR filter - Background removal - Migration (hyperbola fitting/velocity and depth calculation).
Ups... almost forgot the parts about "seeing" the anomaly going all the way to the surface and estimating the size of the anomaly:
1. Anomaly going to the surface
This one is easy! You actually have an anomaly that goes to the surface. Confused?
Think about it: they had to dig a trench and usually you "see" the disturbed soil (it want be as dense as the rest of the field around it).
2. Estimating the size
This one is a tough one!
For the metalic objects it is almost impossible, because they "accumulate" part of the radars energy and start to radiate themselves always looking bigger then they are.
For nonmetalic objects (like in your case) there is a possibility that after doing the migration in a proper way the object/cable will start to look like a vertical elipsoid so measuring in vertical direction will not give you the right dimension but the horizontal value will be close to the diametar of the circle shaped pipe/cable.

BR


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PostPosted: Fri May 21, 2010 2:19 am 
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Joined: Wed Feb 17, 2010 4:56 am
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Location: Jakarta, Indonesia
Hi Bekic

Thx for your answering my question.

Maybe my problem in here I can't do postprocessing the data maximally, because when I convert the raw data (.jpeg) into data with data form (.sgy) using Matlab, I must change the depth from meter (in raw data) into milimeter (in .sgy), beside that most of the software processing GPR data always put the veritical axis (Y axis) in time and not depth. So, when I want to doing like fitting hyperbola to find like permittivity or estimate the diameter of pipe, the result always error, because the input is time not depth. So, the solution I must now the real depth when I'm doing the acquisition. Maybe I must doing survey a lot.

So, thx again Bekic for your attention

Best Regards

Taufik

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PostPosted: Mon May 31, 2010 3:43 am 
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Location: Jakarta, Indonesia
Hi again everyone in here :

I just want to ask :

- the value of the frequency of the GPR device is same meaning for center frequency?, for example like this, the GPR device of mine have frequency 500 MHz, whether the value show the center frequency?

Best Regards

Taufik

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PostPosted: Mon May 31, 2010 6:57 am 
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Joined: Fri Apr 17, 2009 7:52 am
Posts: 379
Location: Boden, Sweden
Hi Taufik,
could you elaborate a bit on your question?
For questions regarding center frequency perhaps you might find this little paper useful:
http://www.geoscanners.com/pdf/gprbw.pdf
Just be aware that center frequency, peak frequency and fundamental frequency are sometimes
used interchangeably although not necessarily have to be the same.
Regards,

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Geoscanners AB
Sweden
http://www.geoscanners.com


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PostPosted: Mon May 31, 2010 7:17 am 
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Joined: Wed Feb 17, 2010 4:56 am
Posts: 18
Location: Jakarta, Indonesia
GeoAdmin wrote:
Hi Taufik,
could you elaborate a bit on your question?
For questions regarding center frequency perhaps you might find this little paper useful:
http://www.geoscanners.com/pdf/gprbw.pdf
Just be aware that center frequency, peak frequency and fundamental frequency are sometimes
used interchangeably although not necessarily have to be the same.
Regards,


I mean like this Reinaldo. Our GPR shielded antenna is 500 MHz, is that value show the center frequency.

But thx for your paper Reinaldo.

Best Regards

Taufik

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