Met Office: Vaisala CL31 Ceilometer
The Met Office own a number of Vaisala CL31 ceilometers used for detecting cloud base heights and also for obtaining backscatter profiles to aid ash cloud detection. The CL31 employs a pulsed diode laser LIDAR (light detection and ranging) technology, which enables it to detect three cloud layers simultaneously.
Fast measurement helps to detect thin cloud patches below a solid cloud base. The CL31 provides a full backscatter profile for data visualization and research purpose. The CL31 beam can be directed either vertically or tilted. The tilting option together with the novel optics design provides enhanced performance during precipitation by improving the protection given by the shield. In the measurement unit, a tilt angle sensor automatically corrects the measured cloud distance reading to vertical cloud base height.