Showing papers by "Robert Meneghini published in 2014"
Cooperative Institute for Research in Environmental Sciences1, Colorado State University2, University of Alabama in Huntsville3, Marshall Space Flight Center4, California Institute of Technology5, Goddard Space Flight Center6, University of Maryland, College Park7, University of Illinois at Urbana–Champaign8, University of Maryland, Baltimore County9, Duke University10
TL;DR: In this article, the authors proposed joint probability distribution functions (joint PDFs) of statistically independent DSD attributes derived from the raindrop mass spectrum, which are then mapped into gamma-shaped DSD parameters.
Abstract: Rainfall retrieval algorithms often assume a gamma-shaped raindrop size distribution (DSD) with three mathematical parameters Nw, Dm, and μ. If only two independent measurements are available, as with the dual-frequency precipitation radar on the Global Precipitation Measurement (GPM) mission core satellite, then retrieval algorithms are underconstrained and require assumptions about DSD parameters. To reduce the number of free parameters, algorithms can assume that μ is either a constant or a function of Dm. Previous studies have suggested μ–Λ constraints [where Λ = (4 + μ)/Dm], but controversies exist over whether μ–Λ constraints result from physical processes or mathematical artifacts due to high correlations between gamma DSD parameters. This study avoids mathematical artifacts by developing joint probability distribution functions (joint PDFs) of statistically independent DSD attributes derived from the raindrop mass spectrum. These joint PDFs are then mapped into gamma-shaped DSD parameter j...
91 citations
TL;DR: In this article, a framework based on measured raindrop size distribution (DSD) data has been developed to assess uncertainties in DSD models employed in Ku-and Ka-band dual-wavelength radar retrievals.
Abstract: A framework based on measured raindrop size distribution (DSD) data has been developed to assess uncertainties in DSD models employed in Ku- and Ka-band dual-wavelength radar retrievals. In this study, the rain rates and attenuation coefficients from DSD parameters derived by dual-wavelength algorithms are compared with those directly obtained from measured DSD spectra. The impact of the DSD gamma parameterizations on rain estimation from the Global Precipitation Measurement mission (GPM) Dual-Frequency Precipitation Radar (DPR) is examined for the cases of a fixed shape factor μ as well as for a constrained μ—that is, a μ–Λ relation (a relationship between the shape parameter and slope parameter Λ of the gamma DSD)—by using 11 Particle Size and Velocity (Parsivel) disdrometer measurements with a total number of about 50 000 one-minute spectra that were collected during the Iowa Flood Studies (IFloodS) experiment. It is found that the DPR-like dual-wavelength techniques provide fairly accurate est...
76 citations
TL;DR: The results indicate that the total precipitation amounts during April 2011 from the KuPR and DPR algorithms are similar to the true values, whereas the estimates from the KaPR data are underestimated.
Abstract: The Global Precipitation Measurement (GPM) Core Observatory will carry a Dual-frequency Precipitation Radar (DPR) consisting of a Ku-band precipitation radar (KuPR) and a Ka-band precipitation radar (KaPR) In this study, “at-launch” codes of DPR precipitation algorithms, which will be used in GPM ground systems at launch, were evaluated using synthetic data based upon the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data Results from the codes (Version 420131010) of the KuPR-only, KaPR-only, and DPR algorithms were compared with “true values” calculated based upon drop size distributions assumed in the synthetic data and standard results from the TRMM algorithms at an altitude of 2 km over the ocean The results indicate that the total precipitation amounts during April 2011 from the KuPR and DPR algorithms are similar to the true values, whereas the estimates from the KaPR data are underestimated Moreover, the DPR estimates yielded smaller precipitation rates for rates less than about 10 mm/h and greater precipitation rates above 10 mm/h Underestimation of the KaPR estimates was analyzed in terms of measured radar reflectivity ( ${\bf Z}_{\bf m}$ ) of the KaPR at an altitude of 2 km The underestimation of the KaPR data was most pronounced during strong precipitation events of ${\bf Z}_{\bf m} \lt {\bf 18}~{\bf dBZ}$ (high attenuation cases) over heavy precipitation areas in the Tropics, whereas the underestimation was less pronounced when the ${\bf Z}_{\bf m}\gt 26~{\bf dBZ}$ (moderate attenuation cases) The results suggest that the underestimation is caused by a problem in the attenuation correction method, which was verified by the improved codes
48 citations