TY  - JOUR
AU  - Ahrends, Hella
AU  - Haseneder-Lind, Rainer
AU  - Schween, Jan
AU  - Crewell, Susanne
AU  - Stadler, Anja
AU  - Rascher, Uwe
TI  - Diurnal Dynamics of Wheat Evapotranspiration Derived from Ground-Based Thermal Imagery
JO  - Remote sensing
VL  - 6
IS  - 10
SN  - 2072-4292
CY  - Basel
PB  - MDPI
M1  - FZJ-2014-05640
SP  - 9775 - 9801
PY  - 2014
AB  - The latent heat flux, one of the key components of the surface energy balance, can be inferred from remotely sensed thermal infrared data. However, discrepancies between modeled and observed evapotranspiration are large. Thermal cameras might provide a suitable tool for model evaluation under variable atmospheric conditions. Here, we evaluate the results from the Penman-Monteith, surface energy balance and Bowen ratio approaches, which estimate the diurnal course of latent heat fluxes at a ripe winter wheat stand using measured and modeled temperatures. Under overcast conditions, the models perform similarly, and radiometric image temperatures are linearly correlated with the inverted aerodynamic temperature. During clear sky conditions, the temperature of the wheat ear layer could be used to predict daytime turbulent fluxes (root mean squared error and mean absolute error: 20–35 W∙m−2, r2: 0.76–0.88), whereas spatially-averaged temperatures caused underestimation of pre-noon and overestimation of afternoon fluxes. Errors are dependent on the models’ ability to simulate diurnal hysteresis effects and are largest during intermittent clouds, due to the discrepancy between the timing of image capture and the time needed for the leaf-air-temperature gradient to adapt to changes in solar radiation. During such periods, we suggest using modeled surface temperatures for temporal upscaling and the validation of image data. 
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000344458000029
DO  - DOI:10.3390/rs6109775
UR  - https://juser.fz-juelich.de/record/172097
ER  -