The ceilometer Vaisala CL51, in operation at CIAO since December 2022, employs an eye-safe diode laser transmitter, emitting short light pulses at 905 nm in zenith or near zenith direction using a single-lens trans-receiver. The light backscattered from atmospheric particles (e.g.: aerosols, clouds, fog and precipitation) is received to detect the attenuated backscatter profiles used for unattended and continuous characterization of aerosol and cloud layering through the troposphere, as well as for the detection of fog and precipitation. The ceilometer profiles have high vertical and temporal resolution, typically in the order of 30 m and 10 s, and a typical measurement range for clouds from 15 m to 12 km above the ground.