Contact and directional radiative temperature measurements of sunlit and shaded land surface components during the SEN2FLEX 2005 campaign

Abstract

Evapotranspiration models require thermodynamic temperatures as a state variable characterizing the surface energy balance. The thermodynamic temperature is calculated using the brightness temperature and the emissivity because no effective method exists to measure thermodynamic temperatures in space and time. A method was therefore developed to measure thermodynamic temperatures in time using contact probes and spatial variations of the thermodynamic temperature using a thermal camera. Using an extraction scheme, the brightness temperatures of canopy and soil were extracted from the thermal images and compared with the contact temperatures. The contact temperatures had similar amplitudes and time‐variability as the brightness temperatures for both components. The slope and offset parameters of a scatter plot were calculated. The slope of the scatter plot was lower than unity for canopy, and higher than unity for soil. Because of the spread in the scatter plot, the emissivities of the components could not be calculated. We conclude that kinematic temperature measurements by contact probes can be a valuable extension to current techniques for measuring continuous component temperatures. The extraction scheme could be a useful tool for extracting the component brightness temperatures for low‐resolution imagery.

Acknowledgements

We thank Wim Timmermans and Rogier van der Velde their help with the goniometric measurements. This work was funded by SRON‐EO‐071.