Mobile Robot Sonar Backscatter Algorithm for Automatically Distinguishing Walls, Fences, and Hedges

Abstract

We present an algorithm to distinguish several types of brick walls, picket fences, and hedges based on the analysis of backscattered sonar echoes. The echo data are acquired by a mobile robot with a single-transducer 50 kHz pulse-echo sonar computer-controlled scanning system packaged as its sensor head. For several locations along a wall, fence, or hedge, a fan of backscatter sonar echoes is acquired, digitized, and stored on a computer as the sonar transducer is swept over a horizontal arc. Off-line, each digitized echo waveform is then rectified, smoothed, and summed to give a measure of the backscatter strength. This backscatter is then plotted versus scan angle, with a series of N-peak deformable templates fit to these data for each scan. The number of peaks in the best-fitting N-peak template indicates the presence and location of retro-reflectors, and allows automatic categorization of the various fences, hedges, and brick walls.