Loading ...
Sorry, an error occurred while loading the content.

AI-GEOSTATS: Variogram estimation

Expand Messages
  • Arie Croitoru
    Dear list members, Following Ruben Roa s email, I would like to add that I did not find any clear criterion to what is the minimum number of data pairs that
    Message 1 of 2 , May 1 2:34 AM
    • 0 Attachment
      Dear list members,

      Following Ruben Roa's email, I would like to add that I did not find any clear criterion to what is the minimum number of data pairs that should be used in each lag and this would certainly affect the variogram uncertainty. I know that a minimum of 30 data pairs is used frequently but my impression is that this is a "rule of thumb". I guess this rule originated from the central limit theorem (?). I found that the lack of a clear criterion might have a big effect on the estimation of the Variogram especially in cases where the data points are non regular and in cases where a non parametric variogram might be considered.

      I would gratefully appreciate any comments on this as well.

      Thanks,

      Arie.


      [Non-text portions of this message have been removed]
    • uleopold
      I do not know if it is a rule of thumb. But it also depends on the variability of your data values. I think it is quite subjective how much pairs you will use.
      Message 2 of 2 , May 1 4:24 AM
      • 0 Attachment
        I do not know if it is a rule of thumb. But it also depends on the
        variability of your data values. I think it is quite subjective how much
        pairs you will use.

        But you should also consider some more robust variogram estimators as correlogram or standardized variograms to see if
        there are no artificial structures or erratic structures caused by extreme
        values or outliers or even trends...

        There is a paper which is quite interesting:

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


        Regards, Ulrich


        On Wed, 1 May 2002, Arie Croitoru wrote:

        > Dear list members,
        >
        > Following Ruben Roa's email, I would like to add that I did not find any clear criterion to what is the minimum number of data pairs that should be used in each lag and this would certainly affect the variogram uncertainty. I know that a minimum of 30 data pairs is used frequently but my impression is that this is a "rule of thumb". I guess this rule originated from the central limit theorem (?). I found that the lack of a clear criterion might have a big effect on the estimation of the Variogram especially in cases where the data points are non regular and in cases where a non parametric variogram might be considered.
        >
        > I would gratefully appreciate any comments on this as well.
        >
        > Thanks,
        >
        > Arie.
        >

        --
        __________________________________________________

        Ulrich Leopold MSc.

        Department of Physical Geography
        Institute for Biodiversity and Ecosystem Dynamics
        Faculty of Science
        University of Amsterdam
        Nieuwe Achtergracht 166
        NL-1018WV Amsterdam

        Phone: +31-(0)20-525-7456 (7451 Secretary)
        Fax: +31-(0)20-525-7431
        Email: uleopold@...
        http://www.frw.uva.nl/soil/Welcome.html

        Check us also out at:
        Netherlands Centre for Geo-ecological Research
        http://www.frw.uva.nl/icg




        --
        * 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
      Your message has been successfully submitted and would be delivered to recipients shortly.