This software enables one to calculate elevation-dependent relative air mass. When imaging a setting or rising Sun on the ground or from space, the shape and the intensity distribution of a captured image are affected by the following three factors: limb-darkening of the solar-disk, atmospheric extinction, and atmospheric refraction. This method is about the relative air mass needed in the estimation of atmospheric extinction.
Several approximate analytical expressions have been proposed for the calculation of relative air mass in the past. Those existing simple, easy-to-use methods allow one to calculate relative air mass only near the surface of the Earth. But they do not apply for the cases where the observation is made on the ground at certain elevation, or from space where the observation height takes a series of different values during sunrise and sunset. An analytical expression was derived for the elevation-dependent relative air mass with the help of a rigorous, multilayer ray-tracing approach.
This work was done by Erkin Sidick of Caltech for NASA’s Jet Propulsion Laboratory.