Radar remote sensing of bare soil surfaces has shown to be very useful for retrieving soil moisture. However, the error on the retrieved value depends on the accuracy of the roughness parameters (RMS height and correlation length). Several studies have revealed that these parameters show a high variability within a field, and therefore, a lot of soil roughness profiles need to be measured to obtain accurate measurements of soil roughness. Yet, in an operational mode, soil roughness measurements are not available
and therefore, for different tillages, possibility distributions of roughness values can be defined. Through inverting the Integral Equation Model, possibility distributions for soil moisture are determined. After transferring these possibilities into probabilities, mean soil moisture values and the uncertainty hereupon
(given by the standard deviation on the retrieved soil moisture values) are obtained. The effect of different roughness types on the retrieval accuracy is assessed. It is found that the accuracy depends on the wetness state of the soil.