Fuzzy system for sound speed estimation in outdoor ultrasonic distance measurements

In outdoor environments, the sound speed depends on the air characteristics, the most important being temperature and humidity. The accuracy of sound speed estimation has direct influence on performance of ultrasonic sensing applications, like those based on the distance measuring and the sound wavelength. In this paper, fuzzy estimation of sound speed is studied, using expert rules generated from the sound speed model. Different fuzzy systems were tested, with various membership functions and fuzzy rules. The selection was made based on the relative error and the mean square error of the fuzzy output, compared with the sound speed model. Accurate estimation of sound speed is obtained. The output surface and the relative error of the selected fuzzy estimator are also presented.