Fuzzy rules of sound speed influence on ultrasonic sensing in outdoor environments

The sound speed is affected by changes in the air properties, such as temperature, pressure, humidity, gas composition, and air turbulence. It has direct influence on the accuracy of distance measuring and the sound wavelength. For many indoor applications, the sound speed in air is considered as constant. For outdoor environments, a constant sound speed generates important errors of distance estimation. Also, for low temperature values, the real distance is smaller than measured distance, and this can be a dangerous situation. The pressure influence on sound speed can be neglected, and the sound speed depends on temperature and relative humidity. In this paper, variations in the speed of sound as a function of air properties are studied, along with their influence on the accuracy of ultrasonic sensing. In addition, fuzzy rules are generated for sound speed values used in outdoor applications.