EFFECT OF AMBIENT CONDITIONS ON CALIBRATION OF HAND-HELD INFRARED RADIOTHERMOMETERS

Hand-held infrared radiothermometers are frequently used in water stre ss studies and in the management of irrigation water to measure soil a nd plant canopy temperatures. Different models of these instruments ar e available but manufacturers' calibration methods are not the same. F ive models of radiothermometers were compared during field experiments on water stress studies on grain sorghum and soybeans at Montpellier, France. The in situ recalibration method advocated by Verbrugghe and Guyot (1992) was used in the field. It was confirmed that field and la boratory calibration equations were not the same. The effects of the m ain climatic parameters influencing the performance of radiothermomete rs were examined. Consequences of calibration methods on the calculati on of certain stress indices, especially the stress degree day (SDD), were also examined.