Ceilometer

[3][4] An optical drum ceilometer uses triangulation to determine the height of a spot of light projected onto the base of the cloud.

Furthermore, the rate at which diffusion happens can be noted by the diminishing part returned to the ceilometer in clear air, giving the coefficient of extinction of the light signal.

[15] In New Zealand, MetService operates a network of laser ceilometers for cloud base measurements at commercial airports.

[16][17][18] Examination of the behavior of ceilometers under various cloud-cover conditions has led to the improvement of algorithms to avoid false readings.

[19] Accuracy of measurement can be impacted by the limited vertical range and areal extent of a ceilometer's area of observation.

[22][23] A study group from Montreal, Canada in 2013 recommended that ceilometers should be installed "close to the landing threshold" for aerodromes with precision approach runways, but also considered their location "at the middle marker or at an equivalent distance" to be acceptable.

[25] In the worst recorded ceilometer non-laser light beam incident, approximately 50,000 birds from 53 different species died at Warner Robins Air Force Base in the United States during one night in 1954.