ABSTRACT
The radiant intensity and spectral distribution of a target source are determined by its temperature and the thermal radiation properties of its surfaces. However, since the radiation leaving the source must pass through some medium, usually the atmosphere, the amount of radiation reaching the receiver is a function of the absorption characteristics of the intervening medium. Although there are many models for predicting the amount of absorption in an atmospheric path, these are, as the name implies, only models rather than exact means of describing atmospheric attenuation. In scattering, energy is taken from the beam and reradiated at the same wavelength as spherical waves from suspended particles in the medium. If there are irregularities on the entering surface, these will also produce scattering. Rayleigh found that the scattered flux is proportional to the inverse fourth power of the wavelength. Consider the rectangle as the x-y plane, whether it be a cloud top or a portion of a spacecraft.
