A microwave radiometer (MWR) is a radiometer that measures energy emitted at sub-millimetre-to-centimetre wavelengths (at frequencies of 1-1000 GHz) known as microwaves. Their primary application has been onboard spacecraft measuring atmospheric and terrestrial radiation, and they are mostly used for meteorological or oceanographic remote-sensing. Their secondary application is also meteorological, as zenith-pointing surface instruments that view the Earth's atmosphere in a region above the stationary instrument.
By understanding the physical processes associated with energy emission at these wavelengths, scientists can calculate a variety of surface and atmospheric parameters from these measurements, including air temperature, sea surface temperature, salinity, soil moisture, sea ice, precipitation, the total amount of water vapor and the total amount of liquid water in the atmospheric column directly above or below the instrument.
The most common form of microwave radiometer was introduced by Robert Dicke in 1946.[1] There is a book-length review of satellite radiometers.[2]
Examples of microwave radiometers on meteorological satellites include the Special Sensor Microwave/Imager, Scanning Multichannel Microwave Radiometer and Microwave Sounding Unit. The Microwave Imaging Radiometer with Aperture Synthesis is an interferometer/imaging radiometer capable of resolving soil moisture and salinity over small regions of surface. The Juno spacecraft, launched in 2011, is planning to characterize the atmosphere of Jupiter using a suite of microwave radiometers.