Use of infrared thermometry to measure canopy-air temperature difference at partial cover to assess crop water stress index

Abstract

A study on the potential for extracting canopy temperature from composite scenes of plant and soil background using infrared thermometry was carried out. Using field and laboratory data, Heilman's equation was tested for its sensitivity and ability to predict actual canopy temperature. Using Idso's approach, crop water stress index values were calculated for partial and full canopies. The study showed that under partial canopy situations calculated leaf temperature is very sensitive to soil background and composite scene temperatures and moderately sensitive to canopy emissivity and cover. Negative values as well as values greater than unity for crop water stress index were calculated for partial canopy conditions. Negative values were also reported for the full canopy cover conditions thus, establishing a need for better estimates of data used in calculation of crop water stress index values. Infrared thermometry does not show much promise as an irrigation scheduling technique for canopies under partial cover using the approach investigated in this study.