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Christopher S. Ruf
and
Calvin T. Swift

Abstract

A tropospheric water vapor density profiling system is presented. The hardware consists of an autocorrelation radiometer (CORRAD) operating over a frequency range from 20.5 to 23.5 GHz. The CORRAD directly measures the autocorrelation of downwelling thermal emission from the atmosphere. The 3 GHz predetection bandwidth of each measurement provides for extremely rapid decorrelation of the noise inherent in all radiometer measurements. This, in turn, allows for high temporal resolution of the water vapor dynamics. Fourier transformation of the raw data produces a brightness temperature spectrum with 100 MHz resolution across the frequency range. Inversion of the radiative transfer integral equation to solve for the water vapor distribution is constrained by the 31 equivalent frequency channels. Previous microwave profilers of the troposphere, with 2 to 5 frequency channels, were much less constrained and the inversion process was accordingly more sensitive to measurement noise. Water vapor profiles estimated by the inversion are in good agreement with coincident radiosonde measurements made by the National Weather Service.

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James B. Mead
,
Robert E. Mcintosh
,
Douglas Vandemark
, and
Calvin T. Swift

Abstract

A recently developed 1.4 mm wavelengh incoherent radar has potential for remote sensing of low reflectivity atmospheric targets for ranges up to several kilometers. Power output of 60 W is achieved using an Extended Interaction Oscillator (EIO). Preliminary reflectivity measurements of clouds and fog for ranges between 36 and 1900 meters are believed to be the first such measurements at this wavelength Limitations on the accuracy of the reflectivity measurements are discussed, highlighting uncertainties due to highly variable attenuation.

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Lihua Li
,
Stephen M. Sekelsky
,
Steven C. Reising
,
Calvin T. Swift
,
Stephen L. Durden
,
Gregory A. Sadowy
,
Steven J. Dinardo
,
Fuk K. Li
,
Arlie Huffman
,
Graeme Stephens
,
David M. Babb
, and
Hans W. Rosenberger

Abstract

Cloud measurements at millimeter-wave frequencies are affected by attenuation due to atmospheric gases, clouds, and precipitation. Estimation of the true equivalent radar reflectivity, Z e , is complicated because extinction mechanisms are not well characterized at these short wavelengths. This paper discusses cloud radar calibration and intercomparison of airborne and ground-based radar measurements and presents a unique algorithm for attenuation retrieval. This algorithm is based on dual 95-GHz radar measurements of the same cloud and precipitation volumes collected from opposing viewing angles. True radar reflectivity is retrieved by combining upward-looking and downward-looking radar profiles. This method reduces the uncertainty in radar reflectivity and attenuation estimates, since it does not require a priori knowledge of hydrometeors' microphysical properties. Results from this technique are compared with results retrieved from the Hitschfeld and Bordan algorithm, which uses single-radar measurements with path-integrated attenuation as a constraint. Further analysis is planned to employ this dual-radar algorithm in order to refine single-radar attenuation retrieval techniques, which will be used by operational sensors such as the CloudSat radar.

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