RE: [ai-geostats] practical range vs range
- Hi Els,
The key question here is the sampling density and how many data will
be included in this search window. If there are many, the screening effect
will greatly attenuate the impact of the data further away, hence using a or
3a won't make a big difference. If data are sparser, then usually I set up my
search strategy in terms of maximum number of data, not maximum search
radius, at least in 2D (in 3D setting the search ellipsoid right is very important).
Although simple kriging weights become zero beyond the range, it is not
the case for ordinary kriging, which is a reason why you shouldn't systematically
discard the observations outside the range of autocorrelation, in particular
if the sampling density is low..
From: Els Verfaillie [mailto:els.verfaillie@...]
Sent: Wed 3/23/2005 5:08 AM
Subject: [ai-geostats] practical range vs range
I want to do ordinary kriging with an anisotropic variogram with GSLIB. My
variogram is an exponential model with a practical range of 1800 m in
direction 50 and 880 m in direction 320. I'm not sure whether I have to use
the practical range (which is 3a) or the value a, which is respectively 733
m and 293 m. Furthermore I wonder which maximum search radius I have to
choose: the 3a or the a value?
Els Verfaillie, PhD student
Renard Centre of Marine Geology - Ghent University
B-9000 Gent - Belgium
tel: +32-9-2644573 fax: +32-9-2644967
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