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AI-GEOSTATS: Non-Monotone Variogram model

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  • Yadollah (Majid) Waghei
    Hello list members My Empirical Variogram for a spatial data set has an cubic like form(see below). Then the ordinary variogram models such as Exponential,
    Message 1 of 4 , May 6, 2001
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      Hello list members
      My Empirical Variogram for a spatial data set has an cubic like form(see below). Then the ordinary variogram models such as Exponential, Gaussian, Linear, Spherical models is not best fit to my data( Because these models are monotone (increasing) functions). Then I need to a suitabe variogram model for such Data.

      A graph of semivariogram
      gamma(h)
      | .
      | .
      | . .
      | . .
      | . . .
      | . . .
      | . ..
      | .
      | .
      | . . . .
      | . . .
      |_________________________________________ h
      Thank you
      Waghei
      Dep.of Biostatistics
      Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111
      Tel:8011001-3872 Fax:8007989
      ___________________________________________________________________________
      Visit http://www.visto.com/info, your free web-based communications center.
      Visto.com. Life on the Dot.


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    • Ulrich Leopold
      Dear Waghei, At first I would not trust only in the traditional semivariogram. You should better use more robust measures to evaluate the semivariogram
      Message 2 of 4 , May 6, 2001
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        Dear Waghei,

        At first I would not trust only in the traditional semivariogram. You
        should better use more robust measures to evaluate the semivariogram
        structures. There are several possibilities like correlogram or other
        standardized variogram estimators (Srivastava, Parker 1989 - see below for
        full reference). They are robust against outliers/extreme values, positive
        skewness. Did you test for a trend?

        In addition, did you try to vary the lag distance? Perhaps you will get a
        better spatial continuity if you increase/decrease it.

        If there should be a periodic structure you could use for variogram
        modelling the periodical or hole effect model. But first you should think
        of the underlying physical processes.

        Hope this helps, Ulrich

        References:

        Srivastava, R.M.; Parker, H.M. 1989: Robust measures of spatial
        continuity. In: Armstrong, M.1989 (Ed.): Geostatistics. Vol.1, Dordrecht,
        p. 295-308.


        On 2001.05.06 12:07:01 +0200 Yadollah (Majid) Waghei wrote:
        > Hello list members
        > My Empirical Variogram for a spatial data set has an cubic like form(see
        > below). Then the ordinary variogram models such as Exponential,
        > Gaussian, Linear, Spherical models is not best fit to my data( Because
        > these models are monotone (increasing) functions). Then I need to a
        > suitabe variogram model for such Data.
        >
        > A graph of semivariogram
        > gamma(h)
        > | .
        > | .
        > | . .
        > | . .
        > | . . .
        > | . . .
        > | . ..
        > | .
        > | .
        > | . . . .
        > | . . .
        > |_________________________________________ h
        > Thank you
        > Waghei
        > Dep.of Biostatistics
        > Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111
        > Tel:8011001-3872 Fax:8007989
        > ___________________________________________________________________________
        > Visit http://www.visto.com/info, your free web-based communications
        > center.
        > Visto.com. Life on the Dot.
        >
        >
        > --
        > * 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
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        >
        >

        --
        ________________________________________________

        Ulrich Leopold MSc.

        Engelstrasse 104
        D-54292 Trier
        Germany

        Phone: +49-(0)651-140764
        E-mail: uleopold@...
        URL: http://www.geocities.com/leop6101/index.htm


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      • WARR Benjamin
        Dear Yadollah, have a look to see if you have any strong outliers using a variogram cloud. Your potential drift may simply be a single erroneous or extreme
        Message 3 of 4 , May 7, 2001
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          Dear Yadollah,

          have a look to see if you have any strong outliers using a variogram cloud.
          Your potential drift may simply be a single erroneous or extreme value,
          which once removed will cause your variogram to stabilise,

          Benjamin Warr
          Research Associate to Prof. Ayres,
          Geostatistician, Environmental Scientist.

          Postal Address:
          Centre for the Management of Environmental Resources (CMER)
          INSEAD
          Boulevard de Constance,
          77305 Fontainebleau Cedex,
          France

          Tel: 33 (0)1 60 72 4456
          Fax: 33 (0)1 60 74 55 64
          e-mail: benjamin.warr@...


          > -----Original Message-----
          > From: Yadollah (Majid) Waghei [mailto:waghei@...]
          > Sent: Sunday, May 06, 2001 12:07 PM
          > To: ai-geostats@...
          > Cc: mohsen_m@...; mohsen_m@...
          > Subject: AI-GEOSTATS: Non-Monotone Variogram model
          >
          >
          > Hello list members
          > My Empirical Variogram for a spatial data set has an cubic
          > like form(see below). Then the ordinary variogram models such
          > as Exponential, Gaussian, Linear, Spherical models is not
          > best fit to my data( Because these models are monotone
          > (increasing) functions). Then I need to a suitabe variogram
          > model for such Data.
          >
          > A graph of semivariogram
          > gamma(h)
          > | .
          > | .
          > | . .
          > | . .
          > | . . .
          > | . . .
          > | . ..
          > | .
          > | .
          > | . . . .
          > | . . .
          > |_________________________________________ h
          > Thank you
          > Waghei
          > Dep.of Biostatistics
          > Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111
          > Tel:8011001-3872 Fax:8007989
          > ______________________________________________________________
          > _____________
          > Visit http://www.visto.com/info, your free web-based
          > communications center.
          > Visto.com. Life on the Dot.
          >
          >
          > --
          > * 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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