CL61 Ceilometer

A Väisälä CL61 is running continuously since July 2021 and recording data for backscatter signals and the depolarisation ratio.

Attenuated backscatter

A ceilometer send out a laser pulse (160 ns) in the near infrared spectrum (910 nm wavelength) in the vertical direction. The electromagnetic waves are scattered and absorbed by atmospheric particles, depending on the particle size, such that hydrometeors give a stronger response than aerosol particles. The backscattered signal is received by the instrument and given the travel time of the pulse the altitude of the backscattering event can be determined.
The CL61 provides a vertical profile every 5 seconds and has a vertical resolution of 4.8 meters.

In addition to the strength of the backscattered signal the CL61 is also capable of determining the polarisation of the backscattered signal, such that the shape of the backscattering objects can be determined and a differentiation between ice crystals and liquid hydrometeors is feasible.

This instrument has been funded by the Carl-Zeiss foundation. We are very grateful for the financial support.