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[ai-geostats] std deviation when using SGSIM

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  • Oriol Falivene
    Hello, We re using SGSIM from GSLIB to create gaussian fields of standard deivation = 1. We realize that the standard deviation is always underestimated,
    Message 1 of 3 , Jul 20, 2004
    • 0 Attachment
      Hello,

      We're using SGSIM from GSLIB to create gaussian fields of standard
      deivation = 1.
      We realize that the standard deviation is always underestimated, tipical
      obtianed values are betwee 0.7 and 0.9.
      How can I get the correct std. dev?

      Regards

      --



      ______________________________________

      Oriol Falivene
      ofaliven@...
      http://www.ub.es/ggac

      tel. (+34) 93 4021373
      fax (+34) 93 4021340

      Fac. de Geologia,
      Univ. de Barcelona
    • Julián Ortiz
      Hello, This may be due to conditioning data that lower the std. dev. of your realizations. If you want to fix this, you could use the program TRANS in GSLIB
      Message 2 of 3 , Jul 20, 2004
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        Hello,

        This may be due to conditioning data that lower the std. dev. of your
        realizations.
        If you want to fix this, you could use the program TRANS in GSLIB and refer
        to the
        paper:

        "Posterior Identification of Histograms Conditional to Local Data, by A. G.
        Journel and W. Xu,
        Mathematical Geology, 26(3):323-359, 1994.

        If you are doing unconditional simulation, the lower std. dev. may be due to
        the size of your
        field as compared to the range of your variogram.

        Best regards,

        Julián Ortiz C., Ph. D.
        Profesor Asistente
        Departamento de Ingeniería de Minas
        Universidad de Chile

        Fono: +56 2 678 4585
        Fax : +56 2 672 3504
        Web : www.ualberta.ca/~jmo1

        -----Mensaje original-----
        De: Oriol Falivene [mailto:ofaliven@...]
        Enviado el: martes, 20 de julio de 2004 4:00
        Para: ai-geostats@...
        Asunto: [ai-geostats] std deviation when using SGSIM


        Hello,

        We're using SGSIM from GSLIB to create gaussian fields of standard
        deivation = 1.
        We realize that the standard deviation is always underestimated, tipical
        obtianed values are betwee 0.7 and 0.9.
        How can I get the correct std. dev?

        Regards

        --



        ______________________________________

        Oriol Falivene
        ofaliven@...
        http://www.ub.es/ggac

        tel. (+34) 93 4021373
        fax (+34) 93 4021340

        Fac. de Geologia,
        Univ. de Barcelona
      • Oriol Falivene
        Thanks Julian, I was doing unconditional simulation and the ranges were to large. I ve made some tests and each range should be at least 1/10 the grid
        Message 3 of 3 , Jul 20, 2004
        • 0 Attachment
          Thanks Julian,

          I was doing unconditional simulation and the ranges were to large. I've made
          some tests and each range should be at least 1/10 the grid dimensions to obtain
          a good match of the standard deviation. There is any literature regarding this
          issue?

          Regards.

          Oriol

          Julián Ortiz wrote:

          > Hello,
          >
          > This may be due to conditioning data that lower the std. dev. of your
          > realizations.
          > If you want to fix this, you could use the program TRANS in GSLIB and refer
          > to the
          > paper:
          >
          > "Posterior Identification of Histograms Conditional to Local Data, by A. G.
          > Journel and W. Xu,
          > Mathematical Geology, 26(3):323-359, 1994.
          >
          > If you are doing unconditional simulation, the lower std. dev. may be due to
          > the size of your
          > field as compared to the range of your variogram.
          >
          > Best regards,
          >
          > Julián Ortiz C., Ph. D.
          > Profesor Asistente
          > Departamento de Ingeniería de Minas
          > Universidad de Chile
          >
          > Fono: +56 2 678 4585
          > Fax : +56 2 672 3504
          > Web : www.ualberta.ca/~jmo1
          >
          > -----Mensaje original-----
          > De: Oriol Falivene [mailto:ofaliven@...]
          > Enviado el: martes, 20 de julio de 2004 4:00
          > Para: ai-geostats@...
          > Asunto: [ai-geostats] std deviation when using SGSIM
          >
          > Hello,
          >
          > We're using SGSIM from GSLIB to create gaussian fields of standard
          > deivation = 1.
          > We realize that the standard deviation is always underestimated, tipical
          > obtianed values are betwee 0.7 and 0.9.
          > How can I get the correct std. dev?
          >
          > Regards
          >
          > --
          >
          > ______________________________________
          >
          > Oriol Falivene
          > ofaliven@...
          > http://www.ub.es/ggac
          >
          > tel. (+34) 93 4021373
          > fax (+34) 93 4021340
          >
          > Fac. de Geologia,
          > Univ. de Barcelona

          --



          ______________________________________

          Oriol Falivene
          ofaliven@...
          http://www.ub.es/ggac

          tel. (+34) 93 4021373
          fax (+34) 93 4021340

          Fac. de Geologia,
          Univ. de Barcelona
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