AI-GEOSTATS: Non-Monotone Variogram model

[Yadollah (Majid) Waghei]

Hello list members
My Empirical Variogram for a spatial data set has an cubic like form(see below). Then 
the ordinary variogram models such as  Exponential, Gaussian, Linear, Spherical models 
is not best fit to my data( Because these models are monotone (increasing) functions). 
Then I need to a suitabe variogram model for such Data.
  
A graph of semivariogram
gamma(h)
|.
|   .
|  .   .
|..
| .. .
|.  .   .  
|  .  ..
|   .
| .
|.   . . .
| . .  .
|_  h
Thank you
Waghei
Dep.of Biostatistics
Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111
Tel:8011001-3872  Fax:8007989
___
Visit http://www.visto.com/info, your free web-based communications center.
Visto.com. Life on the Dot.


--
* To post a message to the list, send it to [EMAIL PROTECTED]
* 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 [EMAIL PROTECTED] 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

Re: AI-GEOSTATS: Non-Monotone Variogram model

[Ulrich Leopold]

Dear Waghei,

At first I would not trust only in the traditional semivariogram. You
should better use  more robust measures to evaluate the semivariogram
structures. There are several possibilities like correlogram or other
standardized variogram estimators (Srivastava, Parker 1989 - see below for
full reference). They are robust against outliers/extreme values, positive
skewness. Did you test for a trend?

In addition, did you try to vary the lag distance? Perhaps you will get a
better spatial continuity if you increase/decrease it.

If there should be a periodic structure you could use for variogram
modelling the periodical or hole effect model. But first you should think
of the underlying physical processes.

Hope this helps, Ulrich

References:

Srivastava, R.M.; Parker, H.M. 1989: Robust measures of spatial
continuity. In: Armstrong, M.1989 (Ed.): Geostatistics. Vol.1, Dordrecht,
p. 295-308.


On 2001.05.06 12:07:01 +0200 Yadollah (Majid) Waghei wrote:
> Hello list members
> My Empirical Variogram for a spatial data set has an cubic like form(see
> below). Then the ordinary variogram models such as  Exponential,
> Gaussian, Linear, Spherical models is not best fit to my data( Because
> these models are monotone (increasing) functions). Then I need to a
> suitabe variogram model for such Data.
>   
> A graph of semivariogram
> gamma(h)
> |.
> |   .
> |  .   .
> |..
> | .. .
> |.  .   .  
> |  .  ..
> |   .
> | .
> |.   . . .
> | . .  .
> |_  h
> Thank you
> Waghei
> Dep.of Biostatistics
> Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111
> Tel:8011001-3872  Fax:8007989
> ___
> Visit http://www.visto.com/info, your free web-based communications
> center.
> Visto.com. Life on the Dot.
> 
> 
> --
> * To post a message to the list, send it to [EMAIL PROTECTED]
> * 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 [EMAIL PROTECTED] 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
> 
> 

-- 


Ulrich Leopold MSc.

Engelstrasse 104
D-54292 Trier
Germany

Phone: +49-(0)651-140764
E-mail: [EMAIL PROTECTED]
URL: http://www.geocities.com/leop6101/index.htm


--
* To post a message to the list, send it to [EMAIL PROTECTED]
* 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 [EMAIL PROTECTED] 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

Re: AI-GEOSTATS: Non-Monotone Variogram model

[Isobel Clark]

> A graph of semivariogram
> gamma(h)
> |.
> |   .
> |  .   .
> |..
> | .. .
> |.  .   .  
> |  .  ..
> |   .
> | .
> |.   . . .
> | . .  .
> |_  h
   ^

Waghei

If this is an omni-directional semi-variogram, then
what you have is a severe case of anisotropy probably
complicated by a strong trend. 

I would hazard a guess that you start to runout of
pairs of samples in one or more directions somewhere
around the ^ above.

Try constructing directional semi-variograms and
post-plotting the data to identify directional
differences.

Isobel Clark
http://uk.geocities.com/drisobelclark


Do You Yahoo!?
Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk
or your free @yahoo.ie address at http://mail.yahoo.ie

--
* To post a message to the list, send it to [EMAIL PROTECTED]
* 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 [EMAIL PROTECTED] 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