Vaisala Ceilometer Technology

LIDAR principle

Ceilometers incorporate diode laser based LIDAR (Light Detection And Ranging) technology for measurement of cloud base height. In the method short light pulses emitted by a laser diode are focused to a collimated beam and transmitted into the atmosphere. As a light pulse traverses in the air part of it is backscattered by aerosols, and the ceilometer measures the amount of backscatter as the function of altitude. Because light is scattered not only by cloud particles but by all aerosols like drops and snowflakes, sophisticated algorithms are needed to resolve the height of cloud base from the backscatter profile.

Novel optics

The Vaisala CT25K and CL31 ceilometers are based on novel coaxial, or single lens optics. As opposed to the traditional ceilometer design in which transmitter and receiver have their own optics, the coaxial design uses common light path for both emitting and receiving, leading to a strong and stable signal for the whole measurement range. As a result,  excellent measurement accuracy is achieved virtually from zero height, i.e. at the low decision heights that really count in aviation safety.