Sonar sensors are widely used in mobile robots applications such as navigat
ion, map building, and localization. The performance of these sensors is af
fected by the environmental phenomena, sensor design, and target characteri
stics. Therefore, the readings obtained from these sensors are uncertain. T
his uncertainty is often modeled by using Probability Theory. However, the
probabilistic approach is valid when the available knowledge is precise whi
ch is not the case in sonar readings. In this paper, the behavior of sonar
readings reflected from walls and corners are studied, then new models of a
ngular uncertainty and radial imprecision for sonar readings obtained from
corners and walls are proposed. These models are represented by using Possi
bility Theory, mainly possibility distributions.