Beat Deuber

A new 22-GHz radiometer for middle atmospheric water vapor profile measurements

We report on the Middle Atmospheric Water Vapor Radiometer (MIAWARA) instrument, a new ground-based 22-GHz-radiometer that provides water vapor profiles with an altitude coverage of 22-80 km. This paper focuses on the instrumentation and calibration of the new instrument. It is a noncooled instrument with a very low receiver noise temperature, even lower than receiver noise temperatures of existing cooled instruments. The calibration of MIAWARA is achieved with so-called tipping-curve and balanced calibration schemes. The combination of these two calibration techniques allows us to set up a different calibration scheme than most of the other, rarely existing, water vapor profile radiometers at 22 GHz without the commonly used liquid nitrogen calibration. With the use of tipping-curve calibrations, the instrument operates as a standalone instrument. This independence of liquid-nitrogen-cooled calibration targets and of other instruments makes MIAWARA a suitable instrument for campaign use. In addition to the instrumental and calibrational description, a validation technique for the tipping-curve calibration is presented. Finally, first results obtained by measurements carried out in the Swiss plateau are reported.

Middle Atmospheric Water Vapour Radiometer (MIAWARA): Validation and first results of the LAPBIAT Upper Tropospheric Lower Stratospheric Water Vapour Validation Project (LAUTLOS‐WAVVAP) campaign

[1] We present a validation study for the ground-based Middle Atmospheric Water Vapour Radiometer (MIAWARA) operating at 22 GHz. MIAWARA measures the water vapor profile in the range of 20–80 km. The validation was conducted in two phases at different geographical locations. During the first operational period the radiometer was operated at middle latitudes in Bern, Switzerland, and the measured water vapor profiles were compared with the HALOE satellite instrument. The agreement between HALOE and MIAWARA was for most altitudes better than 10%. In the second comparison phase, MIAWARA took part in the Lapland Atmosphere-Biosphere Facility (LAPBIAT) Upper Tropospheric Lower Stratospheric Water Vapour Validation Project (LAUTLOSWAVVAP) campaign in early 2004 in the subarctic region of northern Finland. During this campaign, different balloon sondes probed the water vapor content in the upper troposphere and lower stratosphere. The stratospheric water vapor profiles of the fluorescent hygrometer FLASH-B and the NOAA frost point hygrometer mirror in the range of 20–26 km were compared with the lowermost retrieval points of MIAWARA. The agreement between the balloon instruments and MIAWARA was better than 2% for a total number of 10 comparable flights. This showed the potential of MIAWARA in water vapor retrieval down to 20 km. In addition, the northern Finland MIAWARA profiles were compared with POAM III water vapor profiles. This comparison confirmed the good agreement with the other instruments, and the difference between MIAWARA and POAM was generally less than 8%. Finally, the tipping curve calibration was validated with tipping curve measurements of the All-Sky Multi Wavelength Radiometer (ASMUWARA) which was operated 10 months side by side with MIAWARA. The agreement of the tropospheric opacity derived from these tipping curves agree within 1%.

Calibration of a 22-GHz radiometer for middle-atmospheric water vapor measurements: a non-common approach

The Institute of Applied Physics has developed a new ground-based radiometer for measurements of water vapour profiles in the stratosphere and mesosphere. The uncooled instrument, called MIAWARA, has a very good sensitivity and is calibrated using a combination of tipping curve and balancing calibration. Using this combination the instrument can operate as a self calibrating system without the need for routine maintenance. We present a validation technique for the tipping curve calibration and a new approach for the reference absorber design used in the balancing calibration. The uncommon design of the reference absorbers decreases standing wave artifacts and thus enhances the sensitivity of the instrument, leading to a very good altitude coverage in the range of 20 - 80 kilometres.