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879Re: AI-GEOSTATS: Observations with a known standard deviation

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  • Isobel Clark
    Jan 30, 2003

      I presume what you have is a sort of 'analytical
      error' for each sample? That is, the standard
      deviation for two samples at the same location around
      the 'true value' at the same location?

      In this case, you can put the variance down the
      diagonal of your kriging system to obtain optimal
      weights under the uncertainty admitted for your data

      You would need to be careful that the 'analytical
      variance' was not greater than the nugget effect of
      the semi-variogram model.

      The kriging system would be similar to that obtained
      when the sample is not treated as a 'point', but
      rather as a volume. This results in a lower kriging
      variance than using zero on the diagonal, so to
      compensate you should probably add the complete
      'analytical variance' back on to get realistic
      estimation variances.

      There seems to be a lot of confusion in the books (and
      software) about what happens if you have a significant
      replication variance.

      Isobel Clark

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