Optical depth

Optical depth is a measure of transparency. It is defined as the fraction of radiation (or light) that is scattered or absorbed on a path. One way of visualizing optical depth is to think of a fog. The fog between a person and an object that is immediately in front of them has an optical depth of zero. As the object moves away, the optical depth increases until it reaches a large value and the object is no longer visible.

Optical Depth Media

• 

  Aerosol Optical Depth (AOD) at 830 nm measured with the same LED sun photometer from 1990 to 2016 at Geronimo Creek Observatory, Texas. Measurements made at or near solar noon when the sun is not obstructed by clouds. Peaks indicate smoke, dust and smog. Saharan dust events are measured each summer.

• PIA22737-Mars-2018DustStorm-MCS-MRO-Animation-20181030

Other websites

• optical depth equations