| 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. |
