Scattered-light meter
5-4-370
A device which assesses the visibility by measurement of the luminous or radiant flux scattered out of a direct transmission path from the source of radiation, as a result of the presence of particles in the path.
Note: 1 The scattered flux may be measured in a direction at 180 degrees to that of the radiation emitted by the source. The device is then called a back-scatter light meter.
Note: 2 The scattered flux is sometimes measured in a direction making a relatively small angle (between 20? and 50?) with that of the radiation emitted from the source.
This angle is chosen so that the measured flux is approximately proportional to the total scattered flux; the angle selected depends on the range of visibilities which are of interest. The device is then called a forward-scatter light meter.
Note: 3 The scattered flux may be measured over a wide range of scattering angles. In this case the atmospheric sample is within the measuring device. The device is then called a nephelometer.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
