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GEOSTATS: Trends

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  • Christopher David LLoyd
    Hello, I have recently been looking at the issue of dealing with a non-stationary mean in kriging. Attendence at the recent Geostats-UK meeting indicated that
    Message 1 of 1 , Nov 26, 1999
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      Hello,

      I have recently been looking at the issue of dealing with a non-stationary
      mean in kriging. Attendence at the recent Geostats-UK meeting indicated
      that there was some disagreement concerning the use of terminology. In
      particular, universal kriging (or kriging with a trend, KT) is outlined in
      many major texts as a technique which may estimate the trend (or drift)
      on a moving window basis and the variogram is not estimated as part of
      this process (unlike IRF-k kriging where the generalised variogram is
      estimated as a part of the whole process). I would be interested
      to know if this definition of KT is actually disputed between researchers.

      For KT, many researchers consider it unwise to use the variogram of
      residuals from a global polynomial trend. This is presumably because of
      (i) bias in the estimated variogram and (ii) the fact that the modelled
      trend used for the variogram estimation is different to that used for KT.
      However, I am under the impression that some researchers use the variogram
      of residuals from a polynomial trend in this manner. I would be interested
      to know what approaches list members are using to estimate variograms
      where there is a marked trend effect for KT. A more specific issue
      concerns the perceived problems with using median polishing (as outlined in
      Cressie's 'Statistics for Spatial Data') to estimate the variogram in the
      presense of a trend for use with KT (as opposed to median polish kriging).

      This email is really a general attempt at creating a discussion about what
      is clearly a major issue in geostatistics.

      I look forward to comments from list members.

      Best regards,

      Chris Lloyd


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