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Re: GEOSTATS: Geostat: Program for Bimodal distribution.

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  • Pierre Goovaerts
    Hello, Bimodal distributions usually indicate the existence of two populations, and a Gaussian approach is likely not the most appropriate. You could try an
    Message 1 of 3 , Mar 22, 2000
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      Hello,

      Bimodal distributions usually indicate the
      existence of two populations, and a Gaussian
      approach is likely not the most appropriate.
      You could try an indicator approach but don't
      expect a better reproduction of histogram and semivariogram.
      Note that because of the back-transform and provided
      that in the normal space your simulated values follow a standard
      normal distribution, the histogram of simulated sGs values
      should be close to the sample histogram. Large ergodic
      fluctuations (deviations between realization and
      sample statistics) could be due to a large range
      of the semivariogram with respect to the size of
      the domain to be simulated?

      If you really want to generate maps reproducing all the
      statistics you mention, try simulated annealing
      (sasim program in Gslib).

      Pierre Goovaerts
      <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

      ________ ________
      | \ / | Pierre Goovaerts
      |_ \ / _| Assistant professor
      __|________\/________|__ Dept of Civil & Environmental Engineering
      | | The University of Michigan
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      <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>


      On Wed, 22 Mar 2000, Eunjeong Seok wrote:

      > Could you post this, please. Thanks.
      >
      > Hi..
      >
      > I am struggling with an aperture data set of a fracture plane, which shows a
      > bimodal distribution.
      >
      > I have tried Kriging and Gaussian simulation (GSLIB) to recover the aperture
      > structure, but it seems not to maintain both variogram and mean and variance
      > of the samples at the same time .
      >
      > Therefore, I wonder if there is any software which is able to deal with
      > bimodal distribution, and
      > If GSLIB is a right way to go, what kind of consideration do I need and
      > which program is the most appropriate?
      >
      > Thank you in advance..
      >
      > Eunjeong..
      > ------------------------
      > Eunjeng Seok
      > Dept. of Earth Sciences
      > Memorial Univ. of NFLD
      > St. John's, Canada
      > Tel: 1-709-739-7270
      >
      >
      > ______________________________________________________
      > Get Your Private, Free Email at http://www.hotmail.com
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    • Romijn, R.
      Message 2 of 3 , Mar 23, 2000
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        Re: GEOSTATS: Geostat: Program for Bimodal distribution.

        Dear Eunjeong Seok,

        A semivariogram of a bimodal distribution reflects two kinds of variances: 1) the spatial variance between the sample points and 2) the variance between the two populations which form the bimodel distribution. The spatial variance is therefore contaminated with the variance between the two populations.

        One thing you can do is try to identify the factors related to these two populations. When these factors are determined (e.g. mineral composition, direction etc. ) you can correct your data points in such a way the distribution becomes unimodal. A semivariogram of this unimodal distribution wil reflect the spatial variance with less contamination. For the new variogrammodel GSlib is appropriate.

        A second way to handle the problem is simply to do two interpolations of the datapoints of the two populations separately and then subsequently combine these two interpolation results. The drawback of this method is that the number of datapoints per interpolation will be reduced.

        Good luck,


        Guido Ypenburg

        _____________________________________________________

        G.C. Ypenburg
        Engenering department
        Public Works Rotterdam
        Hydrogeology and geostatistics
        EPIV-2.22
        Galvanistraat 15
        PO box 6633
        3002 AP Rotterdam
        tel:    +31 10-489 54 97
        fax:    +31 10-489 45 00


          ----------
          Van:    Pieters, G.
          Verzonden:      woensdag 22 maart 2000 8:35
          Aan:    Ypenburg, G.
          Onderwerp:      FW: GEOSTATS: Geostat: Program for Bimodal distribution.



          ----------
          Van:    Eunjeong Seok[SMTP:ESEOK@...]
          Verzonden:      woensdag 22 maart 2000 4:49:34
          Aan:    ai-geostats@...
          Onderwerp:      GEOSTATS: Geostat: Program for Bimodal distribution.
          Automatisch doorgezonden door een regel

          Could you post this, please. Thanks.

          Hi..

          I am struggling with an aperture data set of a fracture plane, which shows a
          bimodal distribution.

          I have tried Kriging and Gaussian simulation (GSLIB) to recover the aperture
          structure, but it seems not to maintain both variogram and mean and variance
          of the samples at the same time .

          Therefore, I wonder if there is any software which is able to deal with
          bimodal distribution, and
          If GSLIB is a right way to go, what kind of consideration do I need and
          which program is the most appropriate?

          Thank you in advance..

          Eunjeong..
          ------------------------
          Eunjeng Seok
          Dept. of Earth Sciences
          Memorial Univ. of NFLD
          St. John's, Canada
          Tel: 1-709-739-7270


          ______________________________________________________
          Get Your Private, Free Email at http://www.hotmail.com

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