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1966RE: [ai-geostats] practical range vs range

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  • Pierre Goovaerts
    Mar 23, 2005
      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..



      -----Original Message-----
      From: Els Verfaillie [mailto:els.verfaillie@...]
      Sent: Wed 3/23/2005 5:08 AM
      To: ai-geostats@...
      Subject: [ai-geostats] practical range vs range

      Hi list,

      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?

      Any suggestions?



      Els Verfaillie, PhD student
      Renard Centre of Marine Geology - Ghent University
      Krijgslaan 281-S8
      B-9000 Gent - Belgium
      tel: +32-9-2644573 fax: +32-9-2644967
      e-mail: Els.Verfaillie@...
      url: http://www.rcmg.ugent.be/

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