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Sensors 2008, 8(10), 6165-6187; doi:10.3390/s8106165
Article

Two Improvements of an Operational Two-Layer Model for Terrestrial Surface Heat Flux Retrieval

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Received: 1 September 2008; in revised form: 27 September 2008 / Accepted: 28 September 2008 / Published: 1 October 2008
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Abstract: In order to make the prediction of land surface heat fluxes more robust, two improvements were made to an operational two-layer model proposed previously by Zhang. These improvements are: 1) a surface energy balance method is used to determine the theoretical boundary lines (namely ‘true wet/cool edge’ and ‘true dry/warm edge’ in the trapezoid) in the scatter plot for the surface temperature versus the fractional vegetation cover in mixed pixels; 2) a new assumption that the slope of the Tmf curves is mainly controlled by soil water content is introduced. The variables required by the improved method include near surface vapor pressure, air temperature, surface resistance, aerodynamic resistance, fractional vegetation cover, surface temperature and net radiation. The model predictions from the improved model were assessed in this study by in situ measurements, which show that the total latent heat flux from the soil and vegetation are in close agreement with the in situ measurement with an RMSE (Root Mean Square Error) ranging from 30 w/m2~50 w/m2,which is consistent with the site scale measurement of latent heat flux. Because soil evaporation and vegetation transpiration are not measured separately from the field site, in situ measured CO2 flux is used to examine the modeled λEveg. Similar trends of seasonal variations of vegetation were found for the canopy transpiration retrievals and in situ CO2 flux measurements. The above differences are mainly caused by 1) the scale disparity between the field measurement and the MODIS observation; 2) the non-closure problem of the surface energy balance from the surface fluxes observations themselves. The improved method was successfully used to predict the component surface heat fluxes from the soil and vegetation and it provides a promising approach to study the canopy transpiration and the soil evaporation quantitatively during the rapid growing season of winter wheat in northern China.
Keywords: Two-layer model; surface evapotranspiration; surface energy balance; Bowen Radio; trapezoid method Two-layer model; surface evapotranspiration; surface energy balance; Bowen Radio; trapezoid method
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Zhang, R.; Tian, J.; Su, H.; Sun, X.; Chen, S.; Xia, J. Two Improvements of an Operational Two-Layer Model for Terrestrial Surface Heat Flux Retrieval. Sensors 2008, 8, 6165-6187.

AMA Style

Zhang R, Tian J, Su H, Sun X, Chen S, Xia J. Two Improvements of an Operational Two-Layer Model for Terrestrial Surface Heat Flux Retrieval. Sensors. 2008; 8(10):6165-6187.

Chicago/Turabian Style

Zhang, Renhua; Tian, Jing; Su, Hongbo; Sun, Xiaomin; Chen, Shaohui; Xia, Jun. 2008. "Two Improvements of an Operational Two-Layer Model for Terrestrial Surface Heat Flux Retrieval." Sensors 8, no. 10: 6165-6187.



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