Spectral intensity of atmospheric background radiance plays an important part in effects during Earth-sensing and
measuring, for example flood monitoring, resource remote sensing, earthquake forecasting, monitoring of forest fire, etc.
An approximate model for calculating atmospheric radiance was developed with Radiative Transfer theory based on
transmission of energy. In this model, atmospheric radiance is divided into four sections: (1) single scattering radiance
process of solar radiance by atmosphere particulates; (2) multiple scattering radiance of solar radiation by atmosphere
particulates; (3) infrared thermal emission of the path atmosphere; (4) reflected radiance by the Earth's surface.
Computing methods are analyzed deeply, and their analytical expresses are given out, respectively. Particularly, effect of
reflection of the Earth's surface on atmospheric radiance is thoroughly studied and derived.
Finally, atmospheric spectral radiance was calculated for some representatively meteorologic states. The results show
that atmospheric background radiance is mainly composed with scattered radiance of solar radiation by atmospheric
particulates while wavelength is less than 3μm, and with infrared thermal radiance of path atmosphere and effect of the
Earth's surface on atmospheric radiance may be neglectable while wavelength is more than 3 μm.