Cloud base

This device reflects a beam of light off the cloud base and then calculates its distance using either triangulation or travel time.

Alternatively, the cloud base can be estimated from surface measurements of air temperature and humidity by calculating the lifted condensation level.

[2] In well-defined air masses, many (or even most) clouds may have a similar cloud base because this variable is largely controlled by the thermodynamic properties of that air mass, which are relatively homogeneous on a large spatial scale.

In the thermal spectral domain, water is a strong absorber (and thus emitter, according to Kirchhoff's law of thermal radiation); hence clouds exchange thermal radiation between their bases and the underlying planetary surface (land or ocean) by absorbing and re-emitting this infrared radiation at the prevailing temperature – the lower the cloud base, the warmer the cloud particles and the higher the rate of emission.

Cloud base is an important meteorological variable for aviation safety, as it determines whether pilots may use visual flight rules (VFR) or instrument flight rules for take-off and landing.