ASMUWARA, the All-Sky MUlti WAvelength RAdiometer, is a ground-based microwave and infrared radiometer system for hemispherical sky observations. This instrument was developed at the Institute of Applied Physics of the University of Bern and is in operation since summer 2002. The combination of the totally nine microwave radiometer channels at different frequencies, one infrared radiometer and a video camera allows to continuously monitor atmospheric parameters such as the water vapour and liquid water content, temperature profiles, humidity profiles and cloudiness.
Near the centre of the water vapour absorption line at 22.2 GHz the microwave emission of the atmosphere is mainly due to water vapour and liquid water. ASMUWARA has four channels near this absorption line; two of them (at 23.6 and 31.5 GHz) are used to measure the integrated water vapour (IWV) and integrated liquid water (ILW) content of the atmosphere. In the retrieval process, the brightness temperatures are converted to opacities by means of an iterative algorithm. The IWV and ILW contents, in turn, are determined from the opacities with simple linear relations. An additional infrared sensor monitors the cloud-base temperature. With ASMUWARA's capability to make observations in every direction of the sky, maps of the atmospheric water vapour field as well as images of clouds are made.
Another set of four channels of ASMUWARA is situated at the lower edge of the oxygen line complex at 60 GHz. The penetration depth of the microwave radiation at these frequencies varies from some hundred meters to several kilometers. The combination of totally fourty measurements at four frequencies and under ten different zenith angles is evaluated with an optimal estimation algorithm to obtain temperature profiles in the troposphere. The same method is used to determine humidity profiles. Measurements in zenith direction in the optically thin region at 18.75, 22.2, 23.6 and 31.5 GHz are used.
ASMUWARA is currently mounted on a newly-built platform at the Zimmerwald Observatory, about 10km South of Bern. Until Sept. 2006, ASMUWARA was operating on the roof of the Gebäude für Exakte Wissenschaften of the University of Bern. Realtime measurements are not available online for the moment. However, data in near-realtime (until the day before) will soon be accessible through the STARTWAVE database.