12.  Height of the cloud base

12.1  Definitions

Knowledge of cloud ceiling height is of great interest in airport approach areas. Since the transition surface between clear sky and cloud that characterizes the cloud base is often irregular and blurred, there is no real objective definition of this boundary.

Modern measuring instruments use a principle of detecting the level at which significant reflection or backscattering of a light beam occurs. This level is considered to be the transition zone between clear atmosphere and cloud, i.e., the height of the cloud base.