[1] A variational data assimilation algorithm for assimilating land surface temperature (LST) in the Common Land Model (COLM) is implemented using the land surface energy balance as the adjoint physical constraint. In this data assimilation algorithm, the evaporative fraction of soil and canopy is adjusted according to the surface temperature observations. The analysis results from COLM with the LST assimilation algorithm compare well with the field observations from AmeriFlux data at four sites with different land surface conditions. These results indicate that the surface temperature assimilation method is efficient and effective when only one observation for each day is available (e.g., an observation at 1400 local solar time). A sensitivity analysis for the COLM estimation of evapotranspiration (ET) is also carried out, and the impact of the surface temperature data assimilation on the ET estimates is assessed. It is found that except for time periods with a heavy rainfall event, the ET estimates with the surface temperature assimilation once per day during 0800-1600 local solar time compare better with the AmeriFlux ET measurements than do those without the LST data assimilation. This study implies that the data assimilation algorithm for assimilating regional-scale remote sensing LST data into COLM is promising.
Although directional measurements of brightness temperature has made by a number of satellitebased and airborne sensors for a long time, interpretation of such measurements is a difficult task due to the fact that surface radiometric temperatures are resulted from energy balances in multi-scales from leaf and soil to the top of canopy or pixel. In this paper, a non-isothermal Monte-Carlo method based algorithm was proposed to model the angular emission from vegetative canopy and scale radiometric temperatures of foliage and soil to the top of canopy. This approach allows an accurate simulation of multi-reflection between foliage layers, foliage layer and soil surface, and foliage layers and sky, as well as the non-isothermal condition within canopy and between canopy layers and soil surface. Field measurements of directional thermal infrared radiation, which were collected in the Shunyi remote sensing campaign in Shunyi, Beijing in 2001 was used to preliminarily validate this non-isothermal Monte-Carlo algorithm. A reasonable agreement was archived from this validation.
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