An advanced model for predicting clear-air visibility

This article describes a new model to predict clear-air visibility as a function of bearing with respect to the Sun. Its primary use is for aviation forecasting, and it is capable of providing estimates of visual range for any point along an aircraft flight path, using normal output from a numerical forecast model. It is also capable of forecasting line-of-sight visibility along airport approach paths. The model uses Mie theory to predict scattering from the direct solar beam into the line of sight, and combines this with a diffuse and Rayleigh component of the extinction coefficient to provide visual range estimates. The methodology is presented together with some examples of how visibility varies with solar bearing angle. (c) Crown copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd