A NONLINEAR FILTERING APPROACH FOR DETERMINING HYDRAULIC CONDUCTIVITYFUNCTIONS IN-FIELD SOILS

A nonlinear Extended Kalman Filter approach is used to explicitly acco unt for measurement and model uncertainty in field soil hydraulic cond uctivity function determination. The standard deviation that such a pr ocedure provides for hydraulic conductivity, as a function of water co ntent, is estimated from water content and matric potential measuremen ts. These measurements were obtained following 43 days of water redist ribution in a two-layer soil profile previously ponded with water. Exc ept for a brief initial period during redistribution, water content ch anges can be described with a single exponential conductivity function . Also, reducing the frequency of measurements by 50% and 80% would ch ange the mean hydraulic conductivity function less than +/-1 standard deviation, i.e., half an order of magnitude. The filtering scheme, whi ch accounts for both model and measurement uncertainty, provides an im proved description of in situ hydraulic conductivity functions when co mpared with previous methods, which fail to supply fiducial limits of uncertainty.