Visibility and Fog

Diminished visibility is a major cause of traffic accidents on roadways and cancelled or significantly delayed flights at airports. The source of the deterioration in visibility is the presence of aerosol and cloud (fog) particles in sufficient concentrations to attenuate visible radiation. Mitigating the impact of limited visibility requires better understanding the optical properties of aerosols and fog and improved forecasting of such events in order for drivers to be forewarned and airports to better schedule air traffic.

Fog, while being a hazard when causing reduced visibility, is also a beneficial source of water in those regions where there is limited precipitation yet significant fog that can be harvested to provide a source of drinking or irrigation water. The efficiency of harvesting fog depends on the fog droplet sizes and the horizontal wind velocity.

Discoveries that matter

Droplet instruments are specifically designed to measure, both directly and indirectly, the optical properties of aerosols and clouds and the properties of fog precursor aerosols:

• The CCN 100/200 measures fog droplets that form on cloud condensation nuclei (CCN).
• The PAX measures aerosol light extinction and visibility ~ 1/extinction.
• The UHSAS measures the aerosol size distribution from which extinction is derived.
• The FM-120 measures droplet size distribution from which fog extinction is derived.