Ultrasonic sensors enable mobile autonomous systems to obtain information about obstacles in large environments. In the presented work, a 5 cm broad array of three piezo-ceramic ultrasonic transducers is employed for getting two-dimensional impressions of the surroundings. Deviating from the pulse echo measurement techniques used so far the time-continuous transmitting and receiving from modulated pseudo-random sequences are considered. Thus the narrow bandwidth of a piezo-ceramic transducer can be compensated by an increased measuring period. An advanced analysis of the correlated signals allows the rejection of phantoms caused by multiple reflections. Furthermore, a classification of objects such as wall, corner, log or cylinder is possible.