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Jonas

Kriging with logarithmic semivariogram

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I use Kriging and variograms to describe spatial variability of pilot points for HK and RCH in a PEST parameter estimation simulation. I use the log values for both HK and RCH. For one pilot point set it works perfectly fine to use a logarithmic semivariogram, which also looks reasonable. These HK values are in the range between 1e-4 to 1e-6 m/sek.

For pilot point sets with lower values (in the range between 1e-8 and 1e-10) I get the following message when I try to build a logarithmic semivariogram: Warning. There were no points calculated; bad lag parameters! A semivariogram (that is not logarithmic) does however allow me to build a variogram.

I have two questions:

1. What is the reason for this warning?

2. Would it be a significant difference in interpolation between a semivariogram and a logarithmic semivariogram?

I am happy to receive any comments and ideas on these issues.

Kind regards,

Jonas

Edited by Jonas
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From looking at the code it looks like the warning means that there is something wrong with the input lag parameters and that the kriging code could not find points to create the variogram.

As to your second question... The experimental variograms are used as a guide to create a model variogram. This is the variogram used to do the interpolation. I am guessing that your model variograms would be quite different if compared logarithmic to non-logarithmic.

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Hi Jonas.  Did you solve your problem?  I'm having similar issues with my kriging whereby GMS appears to not be writing the Kh values for MODFLOW.  Tech support are looking into it, but it may take a while.  So I was wondering if you had a solution.  Thanks.

 

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Hi Julian,

I decided to use another variogram method than the semi-logarithmic for the cases when I got the error. If you have problems with the Kriging procedure, have you tried one of the recent nightly builds?

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Yes, I have the latest nightly build.  But they are still trying to find the problem, so the build won't include any fix yet.  Thanks.

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