Ultrasonic Temperature Measurement

The paper covers temperature measurement of water averaged over a certain propagation path via the ultrasonic time-of-flight principle. It uses the fact that the speed of sound is a well-studied physical property and is highly temperature-sensitive, thus a very high resolution can be achieved. In addition, since the measurement takes place over a geometrically well-known path, the propagation path, leading to a spatial dependency that offers to also employ tomographic methods in a study. Initial calibration reveals the very high precision attainable by placing two opposing transducers in a cylindrical tank and determining the mean and standard deviation for stationary temperature conditions. It can be shown that transit time measurements with a standard deviation of less than half a nanosecond can be achieved, therefore the temperature can be measured with a resolution of a few thousandth of a Kelvin.