Principle and practice to separate mixed surface temperature using two-temporal phases radiometric temperature

A key point is to separate mixed temperature into soil and crop surface temperatures for inverting transpiration and CO₂ fluxes. We here present a new way of using two-temporal phase information to separate mixed surface temperature in instead of tow-angle data. Soil and canopy surface radiometric temperatures are very close at the time when net radiation is equal to zero. We can summarize that the radiometric temperature difference between soil and mixed pixels are equal to the diurnal amplitude difference between the radiometric temperature of soil and canopy divided by the percent vegetation cover. In practice, the relationship between the diurnal amplitude of the radiometric temperature of the soil and mixed pixels can be found by experiments. Through simultaneous thermal infrared images with high spatial resolution we can also find out the radiometric temperature of the bare soil in mixed pixels as well as its diurnal amplitude for lower resolution images. The method was validated in the experiment of monitoring radiometric temperature of a wheat field in spring of 2000. We also found out this rule by thermal camera in the Shunyi and Yucheng experiments in 2001. Thus this method is feasible based on theory and experiments.