A directional thermal radiance model for multiple scattering over surfaces

Abstract

The multiple scattering effect between heterogeneous non-isothermal surfaces is described rigorously using the configuration factor in engineering thermophysics.Based on the results a directional thermal radiance model is built,and the numerical calculation of the model is discussed.The model is integrated with the gap probability model and applied to a row structure to simulate the change of Directional Brightness Temperature(DBT).The results show that the modeled DBT agrees well with the observed DBT,especially under the condition that the gap probability is very low.It is also shows that the DBT is aggrandized because of the multiple scattering effects,whereas the change of DBT tend to average out.The temperature difference,spatial distribution,emissivity of the components can all lead to the change of DBT.That is to say,the higher of the temperature difference,the craggier of the surface and the lower of the emissivity,the more exquisite DBT changes along with the viewing zenith.The model developed in this paper can explain "hot spot effect" of thermal radiance,and it is confirmed that the existence of "hot spot" is mainly related to the spatial distribution of components' temperature.This model can be used for the study of directional effect on emissivity,the LST retrieval over urban areas and the adjacency effect of thermal remote sensing pixels.