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Humidity
is a highly variable parameter in atmospheric processes
and it plays a crucial role in atmospheric motions on
a wide range of scales in space and time. Limitations
in humidity observation accuracy, as well as temporal
and spatial coverage, often lead to problems in numerical
weather prediction, in particular prediction of clouds
and precipitation. |
Due to these limitations, the verification of humidity
simulations in operational weather forecasts and climate
modeling is also difficult.
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The GPS is a tool initially designed for positioning
and navigation. As widely demonstrated, the GPS can
also provide a reliable estimate of the Zenith Tropospheric
Delay (ZTD) which can be used to derive the integrated
water vapor (IWV) content of the atmosphere.
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It has been demonstrated that the GPS-estimation of
the IWV has an accuracy that is at least comparable
to that of radiosondes and microwave radiometers, which
are presently the primary source of humidity data. In
addition, ground-based GPS receivers are portable and
economic, providing continuous measurements which are
not affected by rain and clouds.
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There
are at least two potential benefits from the GPS observations:
1) an independent data set for validating forecast and
climate models; and 2) an enhanced weather forecasting
system which makes use of the extra humidity information.
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Troposphere
