Strawberry leaf surface temperature dynamics measured by thermal camera in night frost conditions
Estonian University of Life Sciences, Institute of Technology, Department of Energy Application, Kreutzwaldi 56, EE51014 Tartu, Estonia
The aim of the study was to define the strawberry leaf surface and ambient air temperature differences in night frost conditions. The study was carried out at the commercial strawberry field in late autumn at a specific natural climatic situation, corresponding to night frost conditions. Thermal camera FLIR P660 was used for obtaining thermal images and corresponding visual colour images of the strawberry leaves. The images were taken at ten-minute interval. The ambient air temperature, relative humidity, dew point, solar radiation and wind speed data were obtained by Davis Vantage Pro2 weather station. It was estimated that the surface temperature of the specific leaf is comparatively similar at different parts of the specimen and changes noticeably with the variation of solar radiation intensity. The speed of temperature changes was also analysed. During all the measurement period, the considerable difference between the temperature of the leaf and the ambient air temperature was established, especially in absence of solar radiation. The difference of the leaf surface and ambient air temperature reached 8 °C. The study showed that in night frost conditions the plants might be endangered by low temperatures even at the air temperatures above 0 °C due to intensive energy loss by long wave radiation to the sky. It is suggested that the thermal imaging or infrared radiation measurement should be used simultaneously with air temperature measurements for more exact timing of night frost prevention measures at strawberry cultivation.