Microwave Radiometry

MeteoSwiss is using microwave radiometry for measuring vertical profiles of tropospheric temperature and humidity up to an altitude of approximately 6 km and profiles of stratospheric ozone between 20 and 65 km.

The molecules in the atmosphere emit electromagnetic radiation in the microwave region which can be measured by microwave radiometers. The profile of temperature, humidity and ozone can then be derived from the frequency dependence of the measured radiation. Radiometers are automatic instruments and acquire data at a high temporal resolution. MeteoSwiss provides tropospheric temperature and humidity profiles every 10 minutes and stratospheric ozone profiles every 30 minutes.

Measurement of Temperature and Humidity

The microwave radiometer HATPRO from RPG in Payerne
The microwave radiometer HATPRO from RPG in

MeteoSwiss uses two radiometer types to measure temperature and humidity profiles. The temperature profiler TEMPRO and the combined temperature and humidity profiler HATPRO. Both instruments provide every 10 minutes vertical profiles from ground up to approximately 6 km. The average vertical resolution is around 500 m. Temperature and Water vapor profiles are retrieved from radiation measurements in 2 bands (7 channels between 22 and 31 GHz for water vapor profiling and 7 channels between 51 and 58 GHz for Temperature profiling) with a built-in quadratic regression algorithm based on a climatology of Payerne radiosondes.

Application of Temperature Measurements

The temperature profiles allow to detect certain patterns in the atmosphere like temperature inversions in the troposphere. The temperature and humidity radiometers are also used in the meteorological surveillance tool of nuclear power plants (CN-MET).

Measurement of Stratospheric Ozone

The Stratospheric Ozone MOnitoring RAdiometer (SOMORA) measures the ozone volume mixing ratio in the stratosphere and lower mesosphere (20 to 65 km) with a vertical resolution of 8-15 km and a time resolution of 30 min. SOMORA is continuously operated in Switzerland since January 2000 and is delivering data to the Network for the Detection of Atmospheric Composition Change (NDACC).

The ozone vertical distribution is calculated from the measurement of the ozone spectral line at 142.17 GHz. The line intensity is proportional to the mixing ratio of the emitting species and the line width depends on the air pressure (altitude).
The ozone quantity is given as the ratio of the number of ozone molecules with respect to the total number of molecules in a given air volume. The ozone measurements reveal the daily as well as the annual variation of ozone above Switzerland.


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Further information