Differentiating Sonar Reflections from Corners and Planes by Employing an Intelligent Sensor

With conventional time-of-flight sonar ranging systems, it is impossible to differentiate a reflection from a plane and from a rightangle corner reflector. A multitransducer pulse/echo ranging system is described that differentiates these two reflectors by exploiting the physical properties of sound propagation. The amplitudes and ranges of reflected signals for the different transmitter and receiver pairs are processed to determine if the reflecting object is a plane or a right angle corner. In addition, the angle of inclination of the reflector with respect to the transducer orientation can be measured. Reflected signal amplitude and range values, as functions of inclination angle, provide the motivation for the differentiation algorithm. A system using two Polaroid transducers is described that correctly discriminates between corners and planes for inclination angles within *lo" of the transducer orientation. The two-transducer system is extended to a multitransducer array to allow the system to operate over an extended range. An analysis comparing processing effort versus estimation accuracy is performed. This approach is applied to the sonar map building problem. Sonar maps a re generated in which planes and corners a re distinguished by two different symbols that indicate their location and, for the plane, its orientation. Zndex Terms-Acoustics, intelligent sensors, map building, robot navigation, sensors, signal processing, sonar, time-of-flight ranging.