A RULE-BASED SYSTEM TO MAP SOIL PROPERTIES

Conventional soil mapping is Limited in its capabilities in that it pr esents a summary of the soil surveyor's conceptual view of soil variat ion. As such, the method conveys little regarding what is known about the variation of individual soil properties, or the quantitative natur e of their variation. We developed a new method for soil mapping, base d on the concepts employed in the PROSPECTOR mineral exploration syste m, which builds on existing soil surveyor knowledge to construct quant itative statements about individual soil properties via the developmen t of a network of rules. These rules operate within a system of Bayesi an inference to assign the varying probability of occurrence of a soil property of interest within an area, given evidence that relates to i t in a known way. Permissible evidence includes the range of attribute s normally used by a soil surveyor, such as landform, vegetation, land use, or parent material, and can also include remotely sensed digital data. Evidence is weighted according to the uncertainty associated wi th it, and combined to produce a single estimate of probability of a g iven attribute. The relationship between the evidence and prediction i s stated explicitly at each stage of the procedure and is thus repeata ble in a consistent manner. The system has the advantage that while it does not discard the evidence and knowledge used in conventional soil survey, it produces quantitative estimates of the distribution of soi l properties, which can be used for a wide range of applications. The data produced is amenable to storage in geographic information systems and related data bases. As such, it can be updated or enhanced as new information or knowledge becomes available.