Non-Contact Measurement of Space Temperature in Greenhouse Using Acoustic Technique

In this study, an acoustic thermometry in a glasshouse using a sound probe is described. The real time measurement of air temperature is important for the appropriate control of ventilation windows of the uniform cultivation environment in the large scale greenhouse. The sound probe, which consisted of a pair of a loud speaker and a microphone, was used for the temperature measurement. The propagation velocity of the sound is dependent on the air temperature. The velocity is acquired from the time of flight (TOF) of the sound. Mean temperature along the sound probe is measured by the TOF of the sound. This technique was tested using a quarter part of a twin-span glasshouse (60.6 m x 14.8 m) with no crops. The mean temperature along with the distance of 21.0 m was measured by the sound probe for 30 hours. The result showed that the technique was appropriate compared with the simultaneous measurement of eight thermocouples. The result also showed that the effect by solar radiation was negligible. The proposed technique realized the temperature measurement of the large greenhouse.