Dear Diane,
Uncertianty in the variogram has been addressed by several authors:
- Eulogio Pardo-Igúzquiza and Peter Dowd, Variance–Covariance
Matrix of the Experimental Variogram: Assessing Variogram Uncertainty,
Mathematical Geology, volume 33, number 4, p. 397-419, May 2001.
- B. P. Marchant and R. M. Lark, Estimating Variogram Uncertainty,
Mathematical Geology, volume 36, number 8, p. 867-898, November 2004.
As you say, the error in the estimation of the variogram increases with
the lag distance.
The uncertainty in the variogram for different lags can be calculated
under a multiGaussian
assumption, although we know the variogram cannot be negative...
You can check the article we wrote a couple of years ago with Clayton
V. Deutsch, and that appeared in Math. Geology.
- Ortiz C., J., and Deutsch, C. V., Calculation of the Uncertainty
in the Variogram, Mathematical Geology, volume 34, number 2, p.
169-183, February 2002.
Best regards,
Julián Ortiz C.
--
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Julián Ortiz C., Ph. D.
Profesor Asistente
Departamento de Ingeniería de Minas
Universidad de Chile
www.minas.cec.uchile.cl
www.ualberta.ca/~jmo1
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diane poon wrote:
Dear AI-geostats list,
These may be a silly questions...but why do variograms appear without
error bars to each sample variogram lag point?
I understand that each point in the sample variogram illustrates the
mean of all pairs of points at that lag distance in the sample area and
the scatter increases with larger lags.
But how does this not compromise our interpretation of the sample
variogram (i.e. sill, range, etc...)?
Why aren't error bars applicable or shown on variograms like we see in
many other type of statistics?
What are the assumptions?
and where can I cite these from the litterature?
Thank you
Diane
--
The period of greatest gain in knowledge and experience, is the most
difficult period in one's life.
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