From AMS Glossary
The ratio of the extinction cross section (scattering plus absorption) and the 180° backscatter cross section, for either particles or molecules. For particles, it is usually used to characterize an ensemble having some distribution in size. It is generally written as
where σ is the extinction coefficient and ß is the value of the scattering phase function at 180°. The ratio S has units of steradian and can vary from as low as 1 to about 100 sr, depending on the type of particles.
S = σ / ß,
Fernald, F., B. Herman, and J. Reagan, 1972: Determination of aerosol height distributions by lidar. J. Appl. Meteor., 11, 482–489, doi:10.1175/1520-0450(1972)011<0482:DOAHDB>2.0.CO;2.
Term edited 4 April 2017.