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 Post subject: Setting Parameters
PostPosted: Fri Aug 26, 2016 1:37 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
Hello everyone,

I've been studying somethings about GPR, and its parameters (Scan Range, Filters HP/LP, stacks, background remove, and gains).
But I feel like in real use, it's not completely like in a theory...
Exemple: I set stacks to 256, but I have a bad response in radargrama. And, stacks (on theory) should give a better response, cause Signal-noise ratio. The radargrama was okay when I use 1-3 stacks.
Why? What more else it's not like in theory? should I use filters, dewow, backg remove, gains (etc) in aquisition? How can I make the better choice to this?

(If you wanna know, I need to use GPR to detect Ducts. I have a GCB500 e Akulla9000, from Geoscanners).

Thank you!


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 Post subject: Re: Setting Parameters
PostPosted: Mon Aug 29, 2016 7:21 am 
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Joined: Tue Nov 30, 2010 3:21 pm
Posts: 30
Dear Klauscb,
due to the time needed to apply it during the collection, in almost all cases, the GPR units that are currently available on the market do not have a real-time stacking implemented. Most of the time it is a "running average" which means that the stacking is applied to consecutive traces instead of collecting multiple traces at the exactly same spot. Because of this implementation the objects that exist for a long time and in a short area do not change their depth much (like layers) benefit from stacking, while at the same time point targets (objects that exist only at a single place) get distorted or smeared out of the data. In a nutshell, when it comes to GPR, stack=1-16 is good enough for almost all of the surveys you can imagine and in reality anything above 64 is an overkill if you are working with 16-bit data (even a computer logic would have trouble noticing the difference).
As for the overall settings:
- you should use the filters during the collection (set it 1/2 of the center freq. and 2x the center freq - in your case 250MHz/1000MHz)
-dewow you do not need to use with Geoscanners equipment
-background removing is a very non-discriminative filter, so you may end up destroying the information about horizontal reflections without knowing it, much better to leave it off during the collection
-gains you should use to compensate the soil attenuation and make it possible to see some responses already in the field, however be careful not to set the gains too high and create data clipping (if you see trace responses getting outside the trace view window then you know that everything outside of the window is clipped/cut-off=lost information)
Bets regards,


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 Post subject: Setting Parameters
PostPosted: Mon Aug 29, 2016 4:29 pm 
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Joined: Mon Aug 01, 2016 11:29 am
Posts: 16
Thank you,

Understood!

About filters, it was just what I was doing.


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