The greatest distance at which an object with specific characteristics is visible to the naked eye. Ideally, the distant objects used in daytime should be black and visible against the sky. At night, lights of known intensity at known distances are used. These may be assessed with a visibility meter. Such a visual process is now being superseded by the use of an instrument known as a transmissometer to determine atmospheric transparency. See also meteorological optical range.
Subjects: Meteorology and Climatology.