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GEOSTATS: covariance VS. Variogram.

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  • Yaron Felus
    Hi all To all of you asking for summery of answers, I am out of the country right now and will be back after ISPRS congress 7/23, sorry for the delay, I
    Message 1 of 2 , Jun 26, 2000
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      Hi all

      To all of you asking for summery of answers, I am out of the country right
      now and will be back after ISPRS congress 7/23, sorry for the delay, I
      promise to post all the answers and my interpretation when I come back.

      Thanks.

      Yaron A. Felus.
      Research associate.
      The Ohio-State University.
      Department of Civil and Environmental Engineering and Geodetic.

      >I was wandering about section 5.3 of the Geostatistics FAQ.
      >( http://curie.ei.jrc.it/faq/sc_general.html )
      >Which says that it is sometimes advantageous to use the covariance over the
      >Variogram.
      >
      >I have a few references that prove the opposite of this fact for example:
      >
      >Cressie A.C. Noel. and Grondona O. Martin (1992); A comparison of Variogram
      >Estimation with Covariogram Estimation, In The art of statistical Science
      >Edited by K.V. Mardia Jhon pp:191-208, Wiley & Sons Ltd.
      >
      >and also in
      >
      >Cressie N.A.C. (1993) Statistics for spatial data. New York Wiley.
      >
      >Cressie and Grondona (1992) proves that variogram estimation is to be
      >preferred to covariogram estimation; the main reasons for that are:
      >1. In the Kriging process where we estimate the mean of the process and
      >then predict the random process both the variogram estimator and
      >covariogram estimator are biased. However the variogram bias is of smaller
      >order.
      >2. If our data has trend contamination then it has �disastrous effect� on
      >attempts to estimate the covariogram while on the variogram it has a �small
      >upward shift�.
      >
      >Does anybody have a reference (or reason) which supports this statement
      >that the covariance has any advantage over the Variogram ?
      >

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