Infrared Limb Darkening of the Earth from Statistical Analysis of TIROS Data

Abstract

The infrared radiance data obtained from measurements by the TIROS satellites have been used to deduce the limb darkening. Large numbers of data permit a statistical treatment in a matrix of radiance and local zenith angle. It is found that, on the average, the degree of limb darkening is largely independent of the absolute value of radiance. However, examination of the limb darkening as a function of latitude and season shows a significant variation which is related in an unresolved way to the surface and atmospheric temperatures, and to the types and amounts of clouds. An empirical expression is developed to generalize the radiances in terms of the local zenith angle, the latitude and the time of year.