Techniques for increasing the reliability of ultrasonic range measurements are described in this paper. Measurement errors are reduced considering two dominant error sources; environmental instability and random noise. To compensate for alterations in measurements due to surrounding conditions, a small reflector is placed at a known distance in front of the sensor and the measurements of the known distance are used as the reference for correcting the measurements of unknown distances. The conditions to prefer this way of compensation is determined by analyzing probable errors of the measurements. The reliability is increased further by tackling random noise with receivers employed redundantly. Assuming a jointly Gaussian distribution, signals of the receivers are combined to get statistically more accurate estimates. An experimental system is built with 40kHz transducers and the results show considerable reduction of measurement errors.
"Aspects of reliable ultrasonic sensor system design", Proc. SPIE 3201, Sensors and Controls for Advanced Manufacturing, (2 January 1998); doi: 10.1117/12.298012; https://doi.org/10.1117/12.298012