The following paper might also be interesting (it is also stored on the AI-GEOSTATS web site, topic: online papers)
"Performance comparison of geostatistical algorithms for incorporating elevation into the mapping of precipitation" Author; Pierre Goovaerts REFERENCE: Proceedings of, the IV International Conference on GeoComputation, was Mary Washington College in Fredericksburg, VA, USA, 25-28 July 1999. Full paper at http://www.geovista.psu.edu/sites/geocomp99/Gc99/023/gc_023.htm Abstract This paper presents three geostatistical algorithms for incorporating a digital elevation model into the spatial prediction of rainfall: simple kriging with varying local means, kriging with an external drift, and colocated cokriging. The techniques are illustrated using annual and monthly rainfall observations at 36 climatic stations in a 5,000 km2 region of Portugal. Cross validation is used to compare the prediction performances of the three geostatistical interpolation algorithms with the straightforward linear regression of rainfall against elevation and three univariate techniques: Thiessen polygon, inverse square distance, and ordinary kriging. Larger prediction errors are obtained for the two algorithms (inverse square distance, Thiessen polygon) that ignore both elevation and rainfall records at surrounding stations. The three multivariate geostatistical algorithms outperform other interpolators, in particular linear regression, which stresses the importance of accounting for spatially dependent rainfall observations in addition to the colocated elevation. Last, ordinary kriging yields more accurate predictions than linear regression when the correlation between rainfall and elevation is moderate (less than 0.75 in the case study). " Hope this helps, Gregoire "RGN" <[EMAIL PROTECTED]> wrote: > Dear Mr. Silva, > > I think your problem with (un)expected results for different interpolation > methods is not so rare. I had similar problem with (too) small differences > between IDW and Kriging/Cokriging solutions. If you are interested about it > you can find question and answers stored in ai-geostats mailing list in > archive 11/2002 (group.yahoo.com/group/new_ai_geostats/ - question in mail > no.756, complete answers in mail no. 761). > > Maybe only could add from my experience that Cokriging can be sometimes > replaced with Kriging with External Drift. Of course carefully, because as I > understood in theory of Cokriging secondary variable describes behaviour of > primary, and in KED secondary variable has influence on primary. > > But, this mailing list includes many experts with much more experience and > knowledge then I have and probably you will find more useful information in > ai-geostats mailing archives. > > Best regards, > Tomislav Malvic > ------------------------------------ > MSc. Tomislav Malvic, Grad. Eng. of Geol. > INA-Industry of Oil plc. (Naftaplin) > Subiceva 29, 10000 Zagreb, CROATIA > > > > > > > > > > > > > > > ----- Original Message ----- > From: Alvaro Silva > To: [EMAIL PROTECTED] > Sent: Tuesday, January 14, 2003 1:02 PM > Subject: AI-GEOSTATS: Cokriging > > > Dear all, > > I'm comparing some different methods in temperature estimation, i.e. idw, > spline, ordinary and universal kriging and cokriging. I'm doing it in > geostatistical analyst (ARCVIEW 8.1), nevertheless the low errors (by x-val) > presented by all the methods, some give better results. The universal > cokriging (covariable altitude) is the one with low errors and r nearest to > 1, but the map is very close to the other methods's maps. It doesn't reveal > the conexion with altitude like it should (the regression coeficcient > between temperature and altitude is high 0.88). The DEM has 1km resolution, > but the cokriging's map is smooth like the ones from other methods. What can > be wrong? I have already reduced the search elypse in the variable altitude > to the minimum and the points to include also (so i'm doing something like > colocalized cokriging), but the map doesn't reveal much spacial variability. > > Thanks for your attention > > �lvaro > > > > Jos� �lvaro Mendes Pimp�o Alves Silva > Ge�grafo - T�cnico de SIG Geographer - GIS Technician > Departamento de Clima e Ambiente Atmosf�rico Climate Department > Instituto de Meteorologia Portuguese Meteorological Institute > > Rua C do Aeroporto > 1749 - 047 Lisboa > Portugal > > Tel: (+351) 218483961 > Fax: (+351) 218402370 > Email: [EMAIL PROTECTED] > > > -- > * 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 -- * 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
