A new model for the construction of a sonar map in a specular environment has been developed and implemented. In a real world, where most of the object surfaces are specular ones, a sonar sensor surfers from a multipath effect which results in a wrong interpretation of an object's location. To reduce this effect and hence to construct a reliable map of a robot's surroundings, a probabilistic approach based on Bayesian reasoning is adopted to both evaluation of object orientations and estimation of an occupancy probability of a cell by an object. The usefulness of this approach is illustrated with the results produced by our mobile robot equipped with ultrasonic sensors.