Model for angular distribution of sky longwave radiation

The distribution of downward longwave radiation from the sky with the zenith angle is important in the studies of energy budgets and infrared remote sensing of the earth surface. Angular thermal emissivity of the atmosphere (ε(θ)) is often used to describe the angular distribution of sky radiation. There are several empirical and semiempirical models to describe this. This report attempts to verify the Coombes and Harrison model and define the physical meaning of the model parameters according to radiation transfer principles.