Instrument measuring the height of the cloud base above ground level. The instrument uses either triangulation by projecting a light spot onto the cloud base at a slant angle while varying and measuring the slant angle so the light spot appears over the detector located at a distance and looking upwards, or by shooting a laser pulse vertically upwards to the cloud base and measuring the time until the reflected pulse arrives at the detector located next to the laser.
meteorological base parameter sensor
ACTRIS Vocabulary
ceilometer