The diffraction of natural radiation is analyzed with GTD theory and the brightness temperature formula is deduced to calculate the diffraction effects.The numerical results indicate that the natural environment and the sun out the direct viewing field only generate ignorable diffraction temperatures of more less than 1K.Without considering diffraction effects the ray tracing method was introduced to the image simulation of natural scene radiation

the emitting model and illuminating model of natural surface are established

the polarization rotation in ray transmission process are also considered.Real scene of building is simulated at last and validated by comparing with field measurement

which indicates that this simulation model is completely feasible in practice.