Microwave radiometry uses radiation from molecules and water droplets in Earth's atmosphere to determine the content of the atmosphere. A radiometer on the ground recieves microwave radiation from, e.g., water vapour, carbon monoxide and ozone in the atmosphere. The data can be used to, e.g., track atmospheric changes. The technique is similar to the one radio astronomers use to study cosmic gas clouds.
Of particular interest is water vapour, a greenhouse gas whose variations are of great importance for climate research. At Onsala Space Observatory there are two microwave radiometers, called Astrid and Konrad, for measurements of water vapour and water droplets in the lower atmosphere, the troposphere. They monitor radiation from water at two frequences: 21 and 31 GHz. The instruments scan the sky, and the measurements are analyzed to determine the amount of water in the troposphere.
The water vapour radiometer Konrad at Onsala Space Observatory.
The GNSS receiver in the SWEPOS network is seen in the background.
Copyright: Magnus Thomasson
There is also an aeronomy station at the observatory, Onsala Radiometers for Microwave sensing of the Atmosphere (ORMA) with two radiometers measuring gases in the upper atmosphere. ORMA-22 monitors water vapour in the stratosphere and mesosphere at 22 GHz. ORMA-113 has a double sideband receiver and monitors ozone at 111 GHz and carbon monoxide at 115 GHz, both in the mesosphere.
For more information about microwave radiometry, see the web site of ORMA (currently not available).
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