19 May 2015 Summary and analysis of 216 GHz polarimetric measurements of in-situ rain
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The Army Research Laboratory (ARL) has developed a polarimetric frequency-modulated continuous-wave (FMCW) instrumentation radar that has been used to study the polarization and backscatter properties of in-situ rain in the 220 GHz atmospheric window. A summary of the preliminary measurements is presented in this work including an analysis of the co-polarization backscatter and attenuation characteristics measured at 216 GHz. A marginal detection of the copolarization backscatter signature of rain was made during a series of fast-moving, heavy downpour thunderstorm events. A detection limit of -40±3 dB[m2/m3] was found for the VV-polarization cross section per unit volume for rain rates up to 150 mm/hr. Co-polarization (VV- and HH-polarization) attenuation characteristics measured at high rain rates (< 20 mm/hr) were well described by a Joss thunderstorm drop distribution in the high frequency limit, where drop size is much greater than the observation wavelength. Observations at 216 GHz suggest attenuation levels of 8-10 dB/km at rain rates above 20 mm/hr, strengthening previous evidence that attenuation through rain is independent of frequency under high rain rate conditions. Attenuation measurements at lower rain rates (< 20 mm/hr) were qualitatively consistent with both Laws and Parsons and Joss thunderstorm distributions.
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Abigail S. Hedden, Abigail S. Hedden, David A. Wikner, David A. Wikner, Russell W. Bradley, Russell W. Bradley, "Summary and analysis of 216 GHz polarimetric measurements of in-situ rain", Proc. SPIE 9462, Passive and Active Millimeter-Wave Imaging XVIII, 94620G (19 May 2015); doi: 10.1117/12.2177805; https://doi.org/10.1117/12.2177805


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