Evolution of the Fog Droplet Size Distribution Observed by Laser Scattering

Abstract

Scattering of a continuous wave He–Ne laser beam in artificial fog is observed by five photometers at different angles. The measured intensity of the light scattered in the different directions is related to a Γ-type spectral distribution of the droplet sizes during the various evolution stages of the fog. The artificial fog is produced in a 40-m³ chamber, where the main physical parameters (vapor and nuclei concentration, temperature) can be controlled to reproduce the complete evolution process. The fog droplet size spectrum is determined at intervals of about 1 min. The results show that the size distribution shifts towards larger size droplets during condensation, and that the shift is reversed during fog dissipation.