Representing and processing uncertain soil information for mapping soil hydrological properties

Mapping soil hydrological properties for a large area (over 10(4) km(2)) is a difficult problem because the knowledge and data usually available for s uch a task are pervaded by uncertainty and imprecision. Because of this lac k of reliable statistical data a possibility theory approach has been devel oped. The resulting system combines a raster type GIS (geographical informa tion system) with a constraint satisfaction solver: the first playing the r ole of a data base and the latter being used to propagate uncertainty along relations among soil properties. For every point in the area covered, iden tification of the more or less possible soil typological units is performed on the basis of flexible matching between, on the one hand. environmental properties characterizing these units and. on the other, what is known abou t these properties for the location under consideration. For each candidate soil unit, hydrological soil properties, such as the water storage capacit y, can be computed by exploiting numerical relationships linking them direc tly or indirectly to other soil properties. Due to uncertainty the possible values of these variables are obtained by a fuzzy interval calculus that i s implemented as a constraint satisfaction problem (CSP) for computational efficiency. The system can produce maps of the localization of soil units a nd maps of the hydrological soil properties considered with respect to a th reshold value. These maps are presented in a way that accounts for the inhe rent uncertainties in the material processed. (C) 2000 Elsevier Science B.V . All rights reserved.