RANGE information is the basis of many reported ap-plications in the robotics field, from object identification
to process tracking [ 11-[7]. Using pulse-echo techniques,
range is evaluated from x = cT0/2 (c = sound
velocity), by measuring the time interval To between pulse
emission and echo detection. Accuracy of the measurement
depends on the knowledge of c and the correct estimation
of To. While sound velocity shows an almost linear
dependence with temperature which can be easily
compensated [8], for the determination of To a simple
threshold-crossing method is generally used. This leads
to some errors, frequently ignored, which are a consequence
of the relatively long rise time of the waveforms
produced by current low-bandwidth ultrasonic transducers
for operation in air. In fact, the received echoes
reach the threshold level some time after the exact beginning
(added delay), making the target to appear slightly
farther away than it actually is (Fig. 1). This error could
be easily avoided if the added delay were constant, but
amplitude changes produce deviations. To quantify this
error it is useful to model the echo waveform as a damped
sinusoid