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AI-GEOSTATS: Kriging universal

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  • Adrián Martínez Vargas
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    Message 1 of 2 , Feb 14, 2002
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      > I have many questions relate of the universal kriging.
      >
      > Someone can tell my:
      >
      > The variogram we most to use is these create with the residuals (mainly
      > spline residuals)?
      >
      > My preoccupation is relate with the magnitude of the estimation variance,
      > it is underestimate if I use residual variogram?
      >
      > In these case is possible reconvert the residual variogram to wall
      > variogram by addition of the effect of drift previously calculate?
      >
      > The case is that variogram create whit untransformed data is inconsistent
      > by the presence of the inner drift.
      >
      > King regards
      >
      > Adrian Martínez Vargas
      > Ing. Geólogo (profesor)
      > Instituto Superior Minero Metalúrgico (ISMM)
      > Las Coloradas, s/n
      > Reparto Caribe.
      > Moa, Holguín, Cuba
      > CP 83329
      > E. Mail
      > amvargas@...
      >
      >

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    • Isobel Clark
      Adrián ... Yes. Theoretically you should use the residuals calculated by first stage universal kriging. However, there are many published case where authors
      Message 2 of 2 , Feb 21, 2002
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        Adrián

        > > The variogram we most to use is these create with
        > the residuals (mainly spline residuals)?
        Yes. Theoretically you should use the residuals
        calculated by first stage universal kriging. However,
        there are many published case where authors have found
        virtually any method of trend removal to be adequate:
        median polish, spline, polynomial trends and so on.

        > > My preoccupation is relate with the magnitude of
        > the estimation variance,
        > > it is underestimate if I use residual variogram?
        Yes.

        > > In these case is possible reconvert the residual
        > variogram to wall
        > > variogram by addition of the effect of drift
        > previously calculate?
        Not really. If you use polynomial trend surface
        analysis, you can build an Analysis of Variance Table
        to find the 'true' residual variance to inflate the
        model. I prefer to use a cross validation approach, to
        see how much inflation is needed and then check that
        it has been removed.

        > > The case is that variogram create whit
        > untransformed data is inconsistent
        > > by the presence of the inner drift.
        I am not sure what you mean by "inconsistent". It is
        certainly mathematically unstable.

        Isobel Clark
        http://uk.geocities.com/drisobelclark/Contents.html



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