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• ## GEOSTATS: covariance VS. Variogram.

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• Hi list, 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
Message 1 of 2 , Jun 11, 2000
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Hi list,

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 ?

Thank you in advance.

Yaron A. Felus.
Research associate.
The Ohio-State University.
Department of Civil and Environmental Engineering and Geodetic.
________________________________________________________________________
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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
Message 2 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 ?
>

________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

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