Re: AI-GEOSTATS: interpretation/testing robustness of variogram
Three obvious possibilities:
(1) you have a large scale trend which only shows up
when you start taking pairs at larger distances. This
would be the case if your second 'rise' tends to curve
upwards rather than flattening.
(2) you have anisotropy. If you did an
'omni-directional' semi-variogram, your smaller
distances will have pairs from all directions and you
will see an 'average' sort of semi-variogram. When you
go to larger distances you are getting lots of pairs
in whatever direction lies between the two clusters
and not much in any other direction. So your larger
scale semi-variogram may be the one in that direction
(3) you are actually dealing with two different
population groups within the sampled areas. If they
have much the same internal structure but differ from
one another in behaviour, you would get this type of
behaviour. In geological applications, you would look
(perhaps) for a fault line or geological boundary
between the two.
As Pierre says, you must ask some basic questions.
Mine would be: why were those two areas so heavily
sampled with comparatively sparser sampling elsewhere?
Hope this helps
Do You Yahoo!?
Everything you'll ever need on one web page from News and Sport to Email and Music Charts
* To post a message to the list, send it to ai-geostats@...
* As a general service to the users, please remember to post a summary of any useful responses to your questions.
* To unsubscribe, send an email to majordomo@... with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
* Support to the list is provided at http://www.ai-geostats.org