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The Microwave Radiometer (MWR) provides time-series measurements
of column-integrated amounts of water vapor and liquid
water. The instrument itself is essentially a sensitive
microwave receiver. That is, it is tuned to measure the
microwave emissions of the vapor and liquid water molecules in
the atmosphere at specific frequencies.
The MWR receives microwave radiation from the sky at 23.8 GHz
and 31.4 GHz. These two frequencies allow simultaneous
determination of water vapor and liquid water burdens along a
selected path. Atmospheric water vapor observations are made at
the "hinge point" of the emission line where the vapor emission
does not change with altitude (pressure). Cloud liquid in the
atmosphere emits in a continuum that increases with frequency,
dominating the 31.4 GHz observation, whereas water vapor
dominates the 23.8-GHz channel. The water vapor and liquid water
signals can therefore, be separated by observing at these two
frequencies.
Additional information available at
"http://www.arm.gov/docs/instruments/static/mwr.html"
[Summary provided by the Atmospheric Radiation Measurement Program]
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