Airport Installation: On exhibition at the Hanover air show

The Eltro transmissometers for visibility measurement comparison work on the principle of a special photometric double beam. The light beam emitted from the light source is chopped and then divided into two beams by means of a beam splitter; one of them passes through the free atmosphere and then is reflected by a triple mirror. The amplitude of the other one — used as reference beam — is modulated a second time.