Evaluation of Using an Infrared Temperature Sensor for Plant Surface Temperature Based Greenhouse Climate Control

The performance of two infrared (IR) sensors for measuring top canopy temperature was compared with that of thermocouples in varying climatic conditions in winter-spring 2006. These IR sensors were installed in two greenhouse compartments where two low pre-night temperature regimes with temperature integration (TI) were implemented. The repeatability and reproducibility of the IR sensor readings were ±0.33°C and ±0.43°C, and ±0.45°C and ±0.99°C for laboratory and greenhouse settings, respectively. Top canopy temperatures measured by IR sensors in two TI regimes were found to capture correctly the trend and magnitude (±0.2°C) of the temperatures measured by the thermocouples in a diurnal cycle. A slightly higher leaf temperature compared to air in the morning was observed due to thermal radiation from greenhouse heating pipes. Lower leaf temperature readings compared to air temperature with IR sensors were observed during solar noon because of heavy radiation which enhanced evapotranspiration from plant leaf surfaces. The top canopy temperature measurements with IR sensor differed from greenhouse air temperature in different times during a day. Therefore, a different temperature control strategy will be needed when a greenhouse is controlled using plant temperature. The performance of the IR sensors was very satisfactory and outperformed the thermocouples in terms of measurement accuracy and efficiency.