A cloud radar RPG-FMCW-94 designed by Radiometer Physics GmbH (RPG) has been installed at CIAO in December 2021. It is a bi-static Frequency-Modulated Continuous Wave (FMCW) W-band Doppler radar for unattended long term observation of clouds and fog.

Linear polarized continuous radiation is transmitted in the atmosphere, while co- and cross polarized radiation backscattered from atmospheric targets is received to detect the profiles of Doppler spectrum and related moments, used to derive the properties of hydrometeors forming clouds and precipitations.

The radar has a 500 mm diameter antenna emitting continuous microwave power of 1.5 W at 94 GHz. The antenna beam width is 0.56° x 0.56°, the antenna gain is 50 dBi, while the radar sensitivity is -46 dBZ at 5 km 10 sec time resolution. The Doppler velocity resolution is better than 0.04 m/s, while the receiver calibration accuracy is within +/- 1 dB. The radar is also able to perform the 3D scanning of the atmosphere in order to determine wind speeds and hydrometeors’ size distribution and orientation.

Radar profiles typically have a vertical resolution of 15 or 30 m and a temporal resolution of 10 seconds, though higher resolutions are also possible. The typical measurement range is from 50 m to 12 km, although the maximum range can be extended depending on measurement scenario.