Effect of Diurnal and Angular Thermal Infrared Measurements on Field-Scale Evapotranspiration

For precision agriculture, estimation of evapotranspiration (ET) plays a key role in crop water management. ET at spatial scale is highly dependent on the land surface temperature (LST) observations. In this study, the field-scale ET is estimated using ground observed LST, NDVI and albedo measured from the ground based thermal and optical sensing. The morning and afternoon ET showed a difference of 5-31% in homogeneous crop at vegetative stage with the change in LST from 4 to 37% while physiologically matured crops showed change up to 6% with change in LST from 1-7%. The change in ET up to 22% was observed if the LST view zenith angle changes from 10° to 50° from nadir. This study showed that field-scale ET was very sensitive to time of measurement, stage of crop and view angle of LST measurements.