Cloud top

However, this is often inconvenient as this is practically feasible only for isolated clouds in full view of (and some horizontal distance away from) the observers.

An alternative (but also more expensive) approach is to acquire airborne observations either visually or using specific instruments such as a lidar.

Cloud top height may be derived from satellite measurements, either through stereophotogrammetry (using pairs of images acquired at different observation angles) or by converting temperature measurements into estimations of height.

[1] The Cooperative Institute for Meteorological Satellite Studies (CIMSS) provides real-time cloud top pressure maps of the conterminous United States derived from data obtained from the GOES 11 and GOES 12 satellites.

Hence clouds cool down from the top through infrared radiation at the prevailing temperature: the higher the cloud top, the cooler the particles and the lower the rate of emission.