The proposed research seeks funds to investigate a) the measurement uncertainty of in-situ rain measuring devices, b) the characteristics of precipitation in conjunction with physical validation efforts of satellite rainfall algorithms, and c) the retrieval of raindrop size distribution (DSD) from simulated dual-frequency radar (DPR) measurements. For measurement uncertainty, we propose to continue our ongoing efforts to determine the accuracy of disdrometer and rain gauge measurements and relate recent technological developments to the measurement requirements of the upcoming Global Precipitation Mission ground validation (GPM-GV) program. The goal of this segment of the study is to design a conceptual network of disdrometer and gauges where users' requirements will be met. The users of the disdrometer and gauge measurements are the algorithm developers, cloud modelers, hydrologists, and ground validation scientists, and therefore this research is a collaborative effort. For the characteristics of precipitation, we have four different objectives. First, we propose to classify the precipitation systems between climate regimes, between storms, and within a storm through DSD characteristics. While disdrometer measurements will be used to determine the DSD classifications, we will benefit form vertically pointing, scanning Doppler, and polarimetric radar measurements wherever they are available. Second, we propose to investigate the small-scale variability of the DSD and bulk descriptors of rainfall within a field of view of the microwave sensor and a footprint of a space-borne radar. The methodology of this study was developed through an experimental study of the small-scale variability of the DSD within a ground-based radar pixel. Third, we propose to determine the role of rain gauges in Tropical Rainfall Measuring Mission (TRMM) Multi-sensor Precipitation Analysis (TMPA), and Multi-sensor Precipitation Estimation (MPE) products. Both products are operational and are important assets for weather and hydrological forecasting. Fourth, we propose to investigate the physical properties of mixed and frozen particles through in-situ measurements. Specifically, we propose to determine the size distribution, fall velocity, habit, density of snowflakes and the relationships between these properties. For the retrieval of DSD from simulated DPR, we propose to evaluate an algorithm that we developed employing disdrometer DSD measurements from different climate regimes. Our algorithm employs a three-parameter gamma distribution, and our preliminary results show a tight relationship between the shape and slope parameters of the gamma distribution regardless of climate regime. We propose to test our algorithm with independent data sets.
