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Re: GEOSTATS: Sensitivity analysis & geostatistics

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  • Bill Thayer
    Gregoire and the rest of the list, I am interested in using sensitivity analysis and value of information (VOI) analysis to design sampling plans for human and
    Message 1 of 3 , Jan 13, 2000
      Gregoire and the rest of the list,

      I am interested in using sensitivity analysis and value of information
      (VOI) analysis to design sampling plans for human and ecological risk
      assessment. I would be interested in references or thoughts on the subject
      of VOI and spatial statistics.

      VOI is useful when one is more interested in determining the variables that
      have the most effect on the decision to be made (e.g., whether remedial
      action is required; choosing from amongst remedial alternatives) in
      addition to identifying the variables that have the largest effect on the
      uncertainty in a predicted quantity (e.g., soil concentration).













      >Dear all,
      >
      >happy new year to the 1290 subscribers of ai-geostats !
      >
      >2000 has started in a very silent way. I hope this will stimulate a bit
      >the discussions on the list. For what concerns the management of the
      >web pages, I won't be able to make any major updates and changes
      >before March because of technical reasons (unless someone is willing
      >to pay my phone bills to maintain the web pages via modem).
      >
      >I have few questions on the mapping of geostatistical data. I'm working
      >on the mapping of radioactivity in the environment after a Chernobyl type
      >accident. Two approaches to the mapping are clearly needed: the first one
      >should be as fast as possible for immediate counter-measures. The second
      >one allows more time to be taken and is needed for the long-term
      >management of contaminated territories.
      >While the long-management allows the organisation of new sampling
      >campaigns, it is not the case for the short term management. The last will
      >be based on information provided by automated sampling networks.
      >Geostatistics have proven to be adequate methods for the mapping of a
      >variable which is presenting large scale structures (due to the plume
      >of contamination) as well as a strong local variability due to the role
      >played by daily rainfall which is the main factor in the deposition of
      >the radioactivity. Rainfall can occur over very small areas, rendering
      >the description of the deposition more difficult.
      >Geostatistics, however, require many assumptions to be verified and
      >the modelling of the spatial correlation can be problematic. There are
      >many different methods that are solving different problems.
      >So which one should be chosen by default ?
      >Few errors can appear in the data and have a great impact on the
      >structure of the semivariogram. Therefore, the automatic modelling of
      >the spatial correlation should not be an acceptable solution.
      >Neural networks are promising techniques for the automatic mapping
      >of environmental data but they still require to be combined
      >with geostatistical techniques to be really efficient. As far as I know,
      >there are only very few publications where a fully automated technique
      >provides better estimates than ordinary kriging.
      >GIS are now providing more advanced tools for spatial statistics. A
      >possible drawback is the misuse of the functions when used by non
      >experts. This again underlines the need for robust and automated
      >methods. Intensive cross-validation techniques could be a solution
      >for the definition of optimal parameters but, because of the many
      >parameters that have to be tested, takes too much time. Also remains
      >the problem of the risk to apply cross-validation techniques on a dataset
      >that would involve few wrong measurement that can be identified
      >only by expert-knowledge.
      >
      >I believe many answers would be found in works on sensitivity analysis
      >(impact of data, parameters and models on the estimates) of the main
      >spatial interpolation techniques. It would also provide many answers to
      >the debate "what is the best interpolation method".
      >
      >Any references, papers or comments are more than welcome.
      >
      >Best regards
      >
      >Gregoire
      >
      >
      >
      >Gregoire Dubois
      >Section of Earth Sciences
      >Institute of Mineralogy and Petrography
      >University of Lausanne
      >Switzerland
      >
      >Currently detached in Italy
      >
      >http://curie.ei.jrc.it/ai-geostats.htm
      >
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      **************************************************
      William C. Thayer

      Environmental Science Center
      Syracuse Research Corporation
      6225 Running Ridge Road
      North Syracuse, NY 13212-2510
      phone: (315) 452-8424
      fax: (315) 452-8090
      email: thayer@...
      **************************************************

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    • Gerard Heuvelink
      ... Dear Bill, There are lots of references that I could give you, but let me give you a few recent book/proceedings titles that should provide a useful
      Message 2 of 3 , Jan 17, 2000
        > I am interested in using sensitivity analysis and value of information
        > (VOI) analysis to design sampling plans for human and ecological risk
        > assessment. I would be interested in references or thoughts on the subject
        > of VOI and spatial statistics.
        >
        > VOI is useful when one is more interested in determining the variables that
        > have the most effect on the decision to be made (e.g., whether remedial
        > action is required; choosing from amongst remedial alternatives) in
        > addition to identifying the variables that have the largest effect on the
        > uncertainty in a predicted quantity (e.g., soil concentration).

        Dear Bill,

        There are lots of references that I could give you, but let me give you a few
        recent book/proceedings titles that should provide a useful 'introduction', with lots
        of references. Please note that these are references on (spatial)
        sensitivity/uncertainty analysis, not on VOI (with which I am not familiar).

        Chan, K., S. Tarantola and F. Campolongo, 1998, (Proceedings of the) Second
        International Symposium on Sensitivity Analysis of Model Output. Please contact
        Stefano Tarantola (stefano.tarantola@...) who I think will be most willing to
        send you a copy of the book for free.

        Heuvelink, G.B.M., 1998, Error Propagation in Environmental Modelling with GIS.
        London: Taylor & Francis. (Please forgive me for promoting my own work.)

        Lowell, K. and A. Jaton, 1999, Proceedings of the Third Symposium on Spatial
        Accuracy Assessment in Natural Resources and Environmental Sciences. Ann
        Arbor: Ann Arbor Press.

        Please let me also draw your attention to the FOURTH Symposium on Spatial
        Accuracy Assessment in Natural Resources and Environmental Sciences, to be
        held in Amsterdam, 12-14 July 2000 (http://www.gis.wau.nl/Accuracy2000/).

        Finally, it might be interesting for you to get in touch with Daniel Griffith
        (dgriffith@...), a spatial statistician that has published a lot on
        spatial undertainty analysis, or with Steve Stehman
        (svstehma@...), a statistican who is specialised in sampling
        theory, applied to forestry/remote sensing. Both are from Syracuse, so that
        should be convenient.

        I hope this is of use to you, best regards, Gerard Heuvelink

        --------------------------------------------------------------
        Gerard B.M. Heuvelink
        Institute for Biodiversity and Ecosystem Dynamics
        University of Amsterdam
        Nieuwe Prinsengracht 130
        1018 VZ Amsterdam
        The Netherlands

        Tel: +31(0)20-525 7448 (Secretary 7451)
        Fax: +31(0)20-525 7431
        email: g.b.m.heuvelink@...
        http://www.frw.uva.nl/soil/Welcome.html

        Have you recently visited http://www.gis.wau.nl/Accuracy2000 ?
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