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GEOSTATS: colocated samples in cokriging

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  • Stefan Falke
    When applying cokriging, is it required that there be secondary samples colocated with at least some of the primary samples? I have looked at multiple
    Message 1 of 2 , Sep 12, 1998
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      When applying cokriging, is it required that there be secondary samples
      colocated with at least some of the primary samples?
      I have looked at multiple references and none explicitly answer this
      question but all of the examples I've found use secondary data sets that
      are, at least partially, colocated with the primary data set. Is it
      possible to use cokriging on data sets that have no colocated samples?

      Thanks,
      Stefan

      ---------------------------------------
      Stefan Falke
      Graduate Research Assistant
      Center for Air Pollution Impact and Trend Analysis
      Washington University in St. Louis

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    • Pierre Goovaerts
      Stefan, The fact that some of the primary and secondary data must be collocated is not a prerequisite for the application of cokriging itself. It is needed to
      Message 2 of 2 , Sep 13, 1998
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        Stefan,

        The fact that some of the primary and secondary data
        must be collocated is not a prerequisite for the
        application of cokriging itself. It is needed to
        assess and model the spatial dependence between the
        two variables, usually through the computation and modeling
        of direct and cross semivariograms. One way to avoid
        this problem is to work in terms of auto- and
        cross-covariance functions, which can be computed from
        non-colocated sets of primary and secondary data. Note
        that for the application of cokriging, you still have
        to estimate the covariance at zero lag distance,
        which could be done by extrapolating the behavior of
        the first few covariance values to the vertical axis,
        as for the estimation of the nugget effect for semivariogram.

        One situation where cokriging has been applied to non-colocated
        primary and secondary variables is when the two variables
        actually refer to the same attribute measured at two different
        times and the destructive nature of the sampling
        precludes multiple measurements at the same location, see
        the following paper for more details.


        Papritz, A., Fluhler, H., 1994. Temporal change of spatially
        autocorrelated soil properties: optimal estimation by cokriging.
        Geoderma 62, 29--43.

        Regards,

        Pierre


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        On Sat, 12 Sep 1998, Stefan Falke wrote:

        > When applying cokriging, is it required that there be secondary samples
        > colocated with at least some of the primary samples?
        > I have looked at multiple references and none explicitly answer this
        > question but all of the examples I've found use secondary data sets that
        > are, at least partially, colocated with the primary data set. Is it
        > possible to use cokriging on data sets that have no colocated samples?
        >
        > Thanks,
        > Stefan
        >
        > ---------------------------------------
        > Stefan Falke
        > Graduate Research Assistant
        > Center for Air Pollution Impact and Trend Analysis
        > Washington University in St. Louis
        >
        > --
        > *To post a message to the list, send it to ai-geostats@....
        > *As a general service to list users, please remember to post a summary
        > of any useful responses to your questions.
        > *To unsubscribe, send email to majordomo@... with no subject and
        > "unsubscribe ai-geostats" in the message body.
        > DO NOT SEND Subscribe/Unsubscribe requests to the list!
        >

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