EFFICIENT AND RESPONSIBLE USE OF PRIOR INFORMATION IN INVERSE METHODS

Prior information on parameters such as hydraulic conductivity or grou nd water recharge rates is often used to stabilize the inverse problem in parameter estimation, A cautious use of prior information is advis able, however, because it may be biased or unrepresentative of the mod el parameters and/or it may not significantly stabilize the parameter estimates, Procedures are given: (1) to identify the model parameters for which prior information may best stabilize the parameter set; and (2) to identify the model parameters for which errors in the prior inf ormation lead to the smallest possible errors in the final set of para meter estimates, The first case is referred to as the efficient use of prior information; the second case is referred to as the responsible use of prior information, The procedures are based on an analysis of t he model parameter space using response surfaces, multiparameter confi dence regions, and eigenspace analysis, The guidelines lead to the sel ection of prior information on those parameters whose axes are most cl osely aligned with the longest axis of the parameter confidence region . Simple synthetic examples are used to explain the concepts, The adva ntages gained in screening the model parameters to identify those para meters for which prior information will be most efficient and responsi ble in determining the final values of the parameter estimates are dem onstrated in the calibration of a ground water flow and solute transpo rt model for the San Juan Basin, New Mexico.