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

Abstract

In this study, an acoustic thermometry in a glasshouse using a sound probe is described. The realtime measurement of air temperature is important for the appropriate control of ventilation windows of theuniform cultivation environment in the large scale greenhouse. The sound probe, which consisted of a pair of aloud speaker and a microphone, was used for the temperature measurement. The propagation velocity of thesound 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 testedusing a quarter part of a twin-span glasshouse (60.6 m x 14.8 m) with no crops. The mean temperature alongwith the distance of 21.0 m was measured by the sound probe for 30 hours. The result showed that thetechnique was appropriate compared with the simultaneous measurement of eight thermocouples. The resultalso showed that the effect by solar radiation was negligible. The proposed technique realized the temperaturemeasurement of the large greenhouse.