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AI-GEOSTATS: variogram modeling with nested structures

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  • Dobler, Lorenz
    Hello list, I am dealing with heavy metals in upper soil layers of forests. Some of my (indicator) variograms behave like a spherical model at the beginning
    Message 1 of 3 , Feb 12, 2001
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      Hello list,

      I am dealing with heavy metals in upper soil layers of forests. Some
      of my (indicator) variograms behave like a spherical model at the
      beginning but in stead of reaching the sill they behave like a
      power-model for greater distances. I tried
      several power models but they didn't fit the variogram very well.
      Just two questions:

      1. What does this special behavior of the experimental variogram tell
      me about the spatial structure or stationarity?
      2. Can I „mix" a spherical and and a power model to build up one
      nested model?

      Hope somebody can help
      Bye
      Lenz

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    • Heinz Burger
      ... Hello Lorenz, Power models are always suspicious for a trend because from experimental data you can t decide whether the exponent is 2 (not
      Message 2 of 3 , Feb 13, 2001
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        "Dobler, Lorenz" schrieb:

        > Hello list,
        >
        > I am dealing with heavy metals in upper soil layers of forests. Some
        > of my (indicator) variograms behave like a spherical model at the
        > beginning but in stead of reaching the sill they behave like a
        > power-model for greater distances. I tried
        > several power models but they didn't fit the variogram very well.
        > Just two questions:
        >
        > 1. What does this special behavior of the experimental variogram tell
        > me about the spatial structure or stationarity?

        Hello Lorenz,
        Power models are always suspicious for a trend because from experimental
        data you can't decide whether the exponent is < 2 or > 2 (not stationary)

        > 2. Can I „mix" a spherical and and a power model to build up one
        > nested model?

        Linear combinations of admissible models produce admissible models.
        The problem is: what will you do? For kriging you only need a good model
        within the search radius. For an interpretation of the spatial structure of
        your phenomenon you don't need a model-function in every case (except
        for comparison). A detailed trend analysis and resiual analysis (incl.
        variogram) will give more information about local and regional spatial
        structures. The variogram is only one tool among others.

        Herzliche Gruesse,

        Heinz Burger

        *****************************************************
        Dr. Heinz Burger
        Freie Universitaet Berlin
        - Geoinformatik -
        Malteserstr. 74-100
        12249 BERLIN, Germany
        Tel. (49) 30-838-70561 Fax: (49) 30-775-2075
        e-mail: hburger@...-berlin.de
        Web-Seite: http://userpage.fu-berlin.de/~hburger/hb
        ****************************************************



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      • Marco Alfaro
        Dear Lorenz: You cannot use the power model in the case of indicator variograms. The variogram g(h) of a random set (indicator 0 or 1) has the following
        Message 3 of 3 , Feb 16, 2001
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          Dear Lorenz:

          You cannot use the power model in the case of indicator variograms.

          The variogram g(h) of a random set (indicator 0 or 1) has the following relationships (not accomplished by the power variogram):

          g(h) <= 0.5
          g(2h) <= 2g(h)

          Regards,

          Marco



          "Dobler, Lorenz" wrote:

          > Hello list,
          >
          > I am dealing with heavy metals in upper soil layers of forests. Some
          > of my (indicator) variograms behave like a spherical model at the
          > beginning but in stead of reaching the sill they behave like a
          > power-model for greater distances. I tried
          > several power models but they didn't fit the variogram very well.
          > Just two questions:
          >
          > 1. What does this special behavior of the experimental variogram tell
          > me about the spatial structure or stationarity?
          > 2. Can I „mix" a spherical and and a power model to build up one
          > nested model?
          >
          > Hope somebody can help
          > Bye
          > Lenz
          >
          > --
          > * To post a message to the list, send it to ai-geostats@...
          > * As a general service to the users, please remember to post a summary of any useful responses to your questions.
          > * To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
          > * Support to the list is provided at http://www.ai-geostats.org


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