Boundary-Layer Meteorology

, Volume 36, Issue 1, pp 1-17

Radiative surface temperature and energy balance of a wheat canopy

I. Comparison of radiative and aerodynamic canopy temperature
  • N. D. S. HubandAffiliated withDepartment of Physiology and Environmental Science, University of Nottingham, School of AgricultureCrop Protection Division, Univ. of Bristol, Dept. of Agricultural Sciences, Long Ashton Research Station
  • , J. L. MonteithAffiliated withLaboratory for Terrestrial Physics, NASA/Goddard Space Flight Center

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For a stand of winter wheat, radiative canopy temperature measured with an infra-red radiometer was systematically related to a surface temperature derived from air temperature and wind speed profiles. Radiative temperature changed significantly with viewing angle and azimuth, but the influences of sun angle and ground cover were minimised by inclining the radiometer at 55 ° to the vertical and at right angles to the solar beam.

At a standard viewing angle of 55 ° to the zenith, radiative canopy temperature was consistently 1 K cooler than the aerodynamic temperature. The algorithm used to describe this relation contains an effective canopy emissivity which decreases with viewing angle and an effective reflectivity. The observations establish a basis for incorporating canopy surface temperature into formulae for estimating the sensible heat loss from vegetation.