Describes a method to extract multiple acoustic landmarks for the indoor navigation of a mobile robot. The environment is modeled by specular vertical walls. An ultrasonic sensor mounted on the mobile robot scans around the surrounding walls and detects multiple echo pulses. On the horizontal plane at the height of the ultrasonic sensor from the floor, the two-dimensional environment is described by the distance as a function of angle in the scan. Due to the specularity of the walls, the distance function has a manageable number of retroreflective parts that can be used as landmarks. By virtue of the constancy of the relative positions between the ultrasonic sensor and the walls in scanning, the echo pulses reflected from a certain reflection points (RP) have the same time-of-flight in the ultrasonic scan data. The authors determine the position of an RP from the collection of the echo pulses that have the same time-of-flight. The direction to an RP is estimated from the orientation of the ultrasonic sensor at which the maximum magnitude is obtained for the group of echo pulses that correspond to the RP. The mean time-of-flight of the group of echo pulses provides the distance to the RP. Some experimental results are provided to show the validity and the performance of the proposed method.
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