Abstract
This paper proposes the use of a long-span ultrasonic thermometer. Conventional thermometers measure temperature at one spatial point, which is sometimes disturbed by a local turbulence. Since this can cause errors, it is inappropriate for such application as environmental management. The ultrasonic thermometer, which consists of a loud speaker and a microphone, derives the temperature from the time of flight (TOF) of sound along the propagation path as the mean-value of one-dimensional temperature distribution, using cross correlation between transmitted and received signals. In the field experiment performed in a glasshouse, the length of the propagation path is 16.0 m. The temperature (Ts) measured by the ultrasonic thermometer is compared with the mean temperature (Ttc) of five airflow-type thermocouples in the measurement area. Temperature differences (Ttc-Ts) are 0.3 degrees Celsius during daytime and 0.1 degrees Celsius during nighttime, which confirm the accuracy of the proposed method.
