Laser cloud altimeter
A clouds altimeter , also Ceilograph (engl. Ceiling = cloud base ) is a means for determining the cloud height. The lower limit of the cloud cover (cloud base) is measured . The measuring range is sufficient for modern equipment to the edge of the tropopause in about 12,500 meters.
Conventional ceilograph
Without a laser, the cloud base can be determined with a powerful headlight and simple triangular calculations, but only when it is cloudy or at night: a powerful headlight shines vertically upwards. The light spot on the underside of the cloud is then measured by an observation station located at a known distance from the headlight. The angle measured at the ground station between the horizontal and the line of sight to the light spot is used to calculate the height of the cloud base.
Laser ceilograph
The laser ceilograph measures the transit time of a light pulse emitted vertically upwards from the ground by a laser to the cloud cover and back. The height of the clouds can then be calculated from the transit time and the speed of light ( electro-optical distance measurement ).
