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 Post subject: GPR Limitations?
PostPosted: Sat Mar 02, 2013 4:45 pm 
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Joined: Sat Mar 02, 2013 4:41 pm
Posts: 1
    Hi All, I wonder if anyone can help me with some research I am doing for my third year dissertation into the limitations and uncertainties of ground penetrating radar.

    Although my area of study is concerned with trunk road investigations I welcome anybody with any experience of GPR :) .

    I would be very grateful for any help you could offer as I have approached many companies and not heard anything back so far.

    I have prepared a very short questionnaire, below (copy into browser):

    https://docs.google.com/a/york.ac.uk/sp ... UGk3cUE6MQ

    All information obtained in this study will be kept strictly anonymous.

    Thank you very much for your time.


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     Post subject: Re: GPR Limitations?
    PostPosted: Sun Mar 03, 2013 8:49 pm 
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    Site Admin

    Joined: Fri Apr 17, 2009 7:52 am
    Posts: 379
    Location: Boden, Sweden
    Interesting poll, I answered to the questions and would encourage all the others to do so as well.
    Please, do post here your results.
    Thank you.

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


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     Post subject: Re: GPR Limitations?
    PostPosted: Fri Mar 22, 2013 8:25 pm 
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    Joined: Fri Mar 22, 2013 8:05 pm
    Posts: 8
    This should be an interesting study to see. I'm interested in the specifics of conductivity of soils being a factor with the GRP results. I'd like to see which companies take your poll as well. Good luck!


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     Post subject: Re: GPR Limitations?
    PostPosted: Sun Mar 24, 2013 11:36 am 
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    Site Admin

    Joined: Fri Apr 17, 2009 7:52 am
    Posts: 379
    Location: Boden, Sweden
    Hi tbardy21,
    The "quality" of a GPR survey depends on many factors, the most important ones are:
    1. Penetration - you must see the target, if you don't see the target all the other parameters bear no meaning at all
    2. Resolution - you must be able to separate your target from the surroundings objects, if you can't do that then
    you need to ask yourself the question "What am I seeing?".
    3. Noise Level - you must be able to see your target clearly, if the background noise or any clutter will obscure your
    target then there is no point in saying much about it.
    There are other parameters as well, but the above mentioned would play a major roll in your survey.
    Now, the conductivity of the soil is directly affecting penetration because it will be the main factor in the attenuation
    of the EM in the media. Higher attenuation in the media translates into lower penetration in the media,
    therefore affecting directly the "visibility" of the target. There is an exact way of calculating this effect, so it is
    indeed quite predictable in situations when you have a more or less homogeneous media.
    An important consideration here would be that for every set of parameters of conductivity and permittivity of the media
    there is always a "knee frequency" which implies that after that the attenuation is always relatively constant. For
    common soils with conductivity of 5mS/m and relative permittivity of 9 you would get 10MHz as a "knee frequency" after
    that the attenuation is relatively constant and equal to approximately 2.8dB/m. This means that at 10m you get 28dB of
    attenuation in one way and 28dB in the other for a whooping 56dB of attenuation of the initial transmitted EM!
    I hope this can give you an idea of how important the conductivity of the media really is.
    Best regards,

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


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     Post subject: Re: GPR Limitations?
    PostPosted: Fri Apr 26, 2013 4:46 pm 
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    Joined: Fri Mar 22, 2013 8:05 pm
    Posts: 8
    GeoAdmin wrote:
    Hi tbardy21,
    I hope this can give you an idea of how important the conductivity of the media really is.
    Best regards,


    This certainly does give me a better understanding of how important conductivity of the media is, especially with all of those factors. The noise, the soil, the penetration, the resolution, and then all of the other factors that go into this as well. I heard mixed things about the effects of soil as far as what type of mixture will limit the image and which soils won't have any effects on the images.

    Can you expand more on this?


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