Dear list,
While playing around with different software, I encounter different definitions for standardized variograms.
Surfer (which is using the terminology of Variowin), uses the term "standardized semivariogram" for variograms obtained by dividing the semivariance by the lag variance, while GS+ uses the total variance. While the function obtained in GS+ is only a matter of rescaling variograms, allowing so various variograms to be compared, those proposed in Surfer have the same pupose as the local, pairwise and/or general relative variograms (see Isaaks & Srivastava, page 163-170), that is to reduce the influence of local means. Interestingly enough, one may note that very few software propose relative variograms while I, very personally, consider these functions as essential for detecting spatial structures of many environmental variables.
I have thus here two questions about the use of standardized/relative variogram:
1) What is the correct terminology or definition for standardized variograms? (I personally do not like very much the use of "standardized" when the standardisation is only applied to each lag...)
2) The general relative variogram (lag divided by the mean of the lag) has properties that are very similar to the "standardized" variogram (lag divided by the variance of the lag) but both functions differ. How shall one decide what to use and what are the relative properties of these functions?
Thank you in advance for any feedback.
Gregoire
PS: a few points here good be added to Tom Mueller's FAQ on Geostatistical Software Conventions.
__________________________________________
Gregoire Dubois (Ph.D.)
JRC - European Commission
IES - Emissions and Health Unit
Radioactivity Environmental Monitoring group
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