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1802[ai-geostats] variogram analysis

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  • Isobel Clark
    Dec 8, 2004
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      Rajive

      I haven't read the other responses yet, so this may be
      redundant.

      Two possibilities:

      (1) anisotropy: if this is shallow marine data there
      should be a difference between longshore drift and
      off-shore deepening of sea-bed. You have an
      omni-directional semi-variogram. It is possible that
      the sampling grid is irregular enough to be
      highlighting directional differences??

      (2) mega-ripples: I have seen similar behaviour in
      off-shore marine diamonds which tend to hug the bottom
      of trenches or ripples. Major ocean beds have
      mega-ripples on the kilometre scale, which is what you
      are seeing here.

      More worrying, I would say, is the fact that your
      graph is dropping with distance. This suggests that
      you also have some underlying trend (non-stationarity)
      which is causing closely spaced samples to be 'more
      different' than those further apart.

      I notice you are using a log transform. What does your
      probability plot look like?

      Isobel
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