Infrared measurement of canopy temperature and detection of plant water stress |
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| Authors: | M Fuchs |
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| Institution: | (1) Department of Agricultural Meteorology, Agricultural Research Organization, Bet Dagan, Israel |
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| Abstract: | Summary Leaf temperature is directly determined by leaf energy and water balance. If diminished water availability decreases latent heat flux at the leaf surface, a complementary increase of sensible heat will occur and create a larger temperature difference between foliage and air. Radiation, air temperature, humidity and wind speed modify leaf temperature and may mask indications of water stress. The position, inclination and orientation of leaves within the canopy also produce considerable variation of leaf temperature. These factors were incorporated in a linear transpiration model, using physical and physiological characteristics of cotton. Water stress was simulated by imposing a limit value for stomatal conductance. The energy balance equation was solved as a function of angle between leaf and solar beam, to determine leaf temperature frequency distribution. The results show that stress induced temperature rise occurs over a small percentage of the total leaf area. Detection of moderate stress requires a normalizing procedure which takes into account meteorological conditions. The leaf temperature distribution is a better indicator of stress than the average value.The infrared thermometer integrates thermal radiation emitted by the foliage included in its field of view. The model simulated the temperature composition of the field of view as a function of sighting angle and orientation relative to the incident solar beam. The spatial averaging of the signal in the field of view, attenuated the sensitivity of the measurement to water stress. The results also indicated that pointing the infrared thermometer towards the canopy in the same direction as the sun, and at an angle of incidence as close as possible to the solar zenith angle, improved the ability to detect water stress.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 2638-E, 1989 series. This work was supported by grant No. US-1138-86 from the Binational Agricultural Research and Development Fund.With 9 Figures |
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