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GSTAT: Anisotropy
Dear all
I have a data set of Cs-134 deposition in west Cumbria and I have
been attempting to fit a variogram model to the natural log
transformed data in order to undertake some kriging. When assuming
isotropy I don't get a very good variogram model - I can fit a
spherical model, but it doesn't look much better than if I assumed a
nugget variance. Then I fitted a variogram model to the data assuming
a direction of 225 degrees (corresponding the dominant wind direction
perhaps) with a horizontal tolerance of 45 degrees I got a much better
variogram model.
Therefore, I would like to know whether gstat uses this direction and
horizontal tolerance when it undertakes the kriging and estimation of
predicted and variance surfaces. I put in the parameters associated
with anistropy (set alpha=225.0 and set tol_hor=45;) in the command
file and I get the same predicted and variance surfaces as when I
krige without these parameters in the command file.
Many thanks for any help people can provide
Kind regards
simon
S i m o n W r i g h t
Radioecology Section
Institute of Terrestrial Ecology
Merlewood Research Station
Windermere Road
Grange-over-Sands
Cumbria. LA11 6JU
United Kingdom
Telephone: +44 (0)15395 32264
Fax: +44 (0)15395 35941
E-mail: s.wright@ite.ac.uk