A DIGITAL SIGNAL-PROCESSING TECHNIQUE FOR COMPENSATING ULTRASONIC SENSORS

A factor of great importance when assessing the accuracy of ultrasonic rangefinders is the accuracy in the knowledge of the speed of sound, necessary to convert temporal into spatial information. A digital sign al-processing technique for making an ultrasonic transducer array capa ble of automatically compensating for variations in the speed of sound due to temperature or any other atmospheric conditions is proposed an d discussed in this paper. The technique is based on an iterative line arized least-squares estimator, namely an extended Kalman filtering al gorithm, for processing the time-of-flight measurements from a referen ce target whose location is only approximately known. In contrast to o ther well-known techniques, neither additional external sensors for mo nitoring the environment nor accurately positioned reference targets a re required. A sensitivity analysis of the proposed algorithm is perfo rmed through a Monte Carlo simulation study. The theoretical analysis provides a clear-cut picture for understanding the merits of the techn ique under a variety of physical operating conditions. The level of th e measurement noise and the correct calibration of the transducers are proven to be the crucial factors for obtaining estimates of the speed of sound at a prescribed level of accuracy, given a fixed temporal in terval for collecting the measurements. The main conclusions of the si mulation study are confirmed by some real-life results obtained using an experimental tracking sonar device.