"Dobler, Lorenz" schrieb:
> Hello list,
>
> I am dealing with heavy metals in upper soil layers of forests. Some
> of my (indicator) variograms behave like a spherical model at the
> beginning but in stead of reaching the sill they behave like a
> power-model for greater distances. I tried
> several power models but they didn't fit the variogram very well.
> Just two questions:
>
> 1. What does this special behavior of the experimental variogram tell
> me about the spatial structure or stationarity?
Hello Lorenz,
Power models are always suspicious for a trend because from experimental
data you can't decide whether the exponent is < 2 or > 2 (not stationary)
> 2. Can I �mix" a spherical and and a power model to build up one
> nested model?
Linear combinations of admissible models produce admissible models.
The problem is: what will you do? For kriging you only need a good model
within the search radius. For an interpretation of the spatial structure of
your phenomenon you don't need a model-function in every case (except
for comparison). A detailed trend analysis and resiual analysis (incl.
variogram) will give more information about local and regional spatial
structures. The variogram is only one tool among others.
Herzliche Gruesse,
Heinz Burger
*****************************************************
Dr. Heinz Burger
Freie Universitaet Berlin
- Geoinformatik -
Malteserstr. 74-100
12249 BERLIN, Germany
Tel. (49) 30-838-70561 Fax: (49) 30-775-2075
e-mail: [EMAIL PROTECTED]
Web-Seite: http://userpage.fu-berlin.de/~hburger/hb
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