Performance comparison of dual-polarization X-band path attenuation and rainfall microphysical estimates with measured disdrometer raindrop spectra

Recent research has demonstrated the value of polarimetric measurements for the correction of rain-path attenuation at X-band radar frequency and the estimation of rain parameters including drop-size distributions (DSD). The standard remotely-sensed precipitation products, from large operational Sor C-band network radars, have spatial resolutions that are often too coarse to reveal hydrological important spatial variability that compromise the prediction of floods. Dual-polarization X-band radar is a potential solution as a gap filling data source for such operational weather radar networks. The major issue in Xband rainfall estimation studies is the atmospheric attenuation effect. Measurements at X-band undergo severe co-polar (AH) and differential (ADP) attenuation that can cause significant reduction of the horizontal reflectivity (ZH) and differential reflectivity (ZDR) signal, which must be corrected because it introduces errors in the rainfall estimation. The fundamental aspect that brought X-band back to the interest of hydrometeorologists for rainfall estimation is that the horizontal versus vertical polarization differential phase shift ΦDP measurement can be used for the effective estimation of specific copolar, AH, and differential, ADP, attenuation profiles. Attenuation corrected profiles are then used to derive the two parameters of the normalized gamma DSD model, that is, intercept (NW) and mean drop diameter (D0) while the third one (shape parameter μ) is calculated using the constrained μ – D0 relation. This work will focus on the use of National Observatory of Athens’ (XPOL) X-band weather radar and 2D videodisdrometer (2DVD) observations, collected during the 2008-2009 in the urban area of Athens, Greece. The efforts are devoted to first (a) evaluate the performance of a newly devised attenuation correction scheme using coincident XPOL observations with measured spectra from a 2DVD, and then (b) compare a new optimized rainfall and drop-size distribution estimation algorithm with already published algorithms. These algorithms are evaluated and intercompared on the basis of in-situ disdrometer spectra observations.