Ground-based radiometric observations of atmospheric emission at 20.6, 31.65, and 90.0 GHz

The Wave Propagation Laboratory (WPL) has designed, constructed, and field tested several ground-based microwave radiometers to observe the atmosphere. Extensive experience has been gained by using both zenith-viewing and steerable dual-frequency instruments operating at 20.6 and 31.65 GHz. These instruments provide unique and meteorologically useful observations of precipitable water vapor and integrated cloud liquid. Perhaps equally as useful are the microwave attenuation characteristics that these devices can easily provide. The WPL extended its radiometric capabilities by adding a channel at 90.0 GHz to the steerable and transportable radiometer. All three channels on this radiometer have equal beamwidths of 2.5 degrees , and point in the same direction from the same location; hence, they are capable of simultaneously measuring emission and deriving attenuation for the same volume of air. Examples are presented of some of the data taken with the new system at San Nicolas Island, California, USA, and at Denver, Colorado, USA. From these data, several statistical and physical quantities, relevant to radio propagation studies, are derived and compared with theory.<
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