Abstract Estimation of refractivity profiles from radar clutter return is discussed. Through simulation andexperimental results it is shown that the radar clutter return can be used for extracting refractivityprofiles. Of particular interest is the uncertainty in these estimates and it is demonstrated how theseparameters can be used for radar performance prediction. Research Summary The goal of this project was to develop inversion approaches that enable the estimation of refractivityprofiles and the associated uncertainty. Further to develop methods for mapping the refractivityparameters and their associated uncertainty into propagation.The results of this reseach are documented in five refered jornal papers [ 1-6] and one conferenceproceeding [7].Our inversion approach has mainly been based on SAGA and focused on estimation of the parameterscorresponding to the field that gives the best fit to the data. We have concentrated on demonstrating thefeasibility of RFC using an efficient 11-parameter description of the environment. The quality of theinversion was addressed by comparing the field using the estimated parameters to a measured field [1-6]. Little has been done to indicate the quality of the solution for each parameter, either with thevariance of parameter-estimate or preferably the complete a posteriori distribution. We have alreadydone much work on this in an ocean acoustic context [Gerstoft 98], but this has not been explored in