Nicoletta Roberto

Use of the GPM Constellation for Monitoring Heavy Precipitation Events Over the Mediterranean Region

Precipitation retrievals exploiting the available passive microwave (PMW) observations by cross-track and conically scanning satellite-borne radiometers in the Global Precipitation Measurement (GPM) mission era are used to monitor and characterize heavy precipitation events that occurred during the Fall 2014 in Italy. Different physically based PMW precipitation retrieval algorithms are used: the Cloud Dynamics and Radiation Database (CDRD) and Passive microwave Neural network Precipitation Retrieval (PNPR), used operationally in the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on support to Operational Hydrology and Water Management (H-SAF), and the National Aeronautics and Space Administration (NASA) Goddard PROFiling algorithm (GPROF). Results show that PMW precipitation retrievals from the GPM constellation of radiometers provide a reliable and quantitative description of the precipitation (instantaneous and on the daily scale) throughout the evolution of the precipitation systems in the Mediterranean region. The comparable relative errors among gauges, radar, and combination of radiometer overpasses legitimize the use of PMW estimates as a valuable and independent tool for monitoring precipitation. The pixel-based comparison with dual-polarization radars and raingauges indicates the ability of the different sensors to identify different precipitation areas and regimes (0.60 <; POD <; 0.76; 0.28 <; FAR <; 0.45; 0.42 <; ETS <; 0.59;-1.6 mm/h <; ME <; 1.1 mm/h}, with values depending on the radiometer and on the precipitation product). This is particularly relevant in the presence of complex orography in proximity of coastal areas, as for the analyzed cases. The different characteristics of the radiometers (i.e., viewing geometry, spatial resolution, channel assortment) and of retrieval techniques, as well as the limitations of the ground-based reference datasets, are taken into consideration in the evaluation of the accuracy and consistency of the retrievals.

Validation of the Advanced Polarimetric Doppler Weather Radar Simulator with Polar55C real observations

A preliminary validation of the Advanced Polarimetric Doppler Weather Radar Simulator (APDWRS) with real data is described in this paper. The APDWRS is used to reproduce an observation of a severe storm event which took place on the 15th of October 2012 over the Tyrrenian coast. One PPI scan performed by the dual polarization C-band Polar 55C weather radar at 17:30 UTC is simulated using APDWRS with meteorological data from the Weather Research and Forecast (WRF) model as input. The validity of the simulation is then compared both in the spatial domain and statistically observing the differences in the relationships between observables in real and simulated case.

Analysis of precipitation in repeated acquisitions collected by the COSMO SkyMed constellation in polarimetric mode

Effects of rain in SAR images have been noted since early missions. For SARs at X-band such as the satellites of the Italian Space Agency constellation COSMO SkyMed or the DLR TerraSAR-X, SAR returns from surface are attenuated by precipitation that gives a specific signature in SAR images that depend on polarization. Attenuation, jointly with a reduced space resolution determined by the Doppler spectrum of precipitation returns, limits the capability of detecting surface features during storms. On the other hand, such precipitation signature could be used for atmospheric studies or precipitation measurements. Characteristics induced by precipitation on polarimetric COSMO SkyMed images collected have been detected and analyzed. The analysis methodology exploits also the availability of coincident measurements of precipitation from ground based radars, used to reconstruct the component of SAR return due to precipitation.

Effects of precipitation on images collected using different operational modes of Cosmo Sky Med

The 4-satellite constellation Cosmo Sky Med of the Italian Space Agency is providing high quality observations suitable for many applications in “all weather” conditions. However, Cosmo Sky Med SARs use a frequency at X-band (9.6 GHz) for which attenuation due propagation through precipitation is not negligible and can affect several SAR applications. In some conditions, especially heavy thunderstorms, precipitation effects can be significant, masking features of interest of the observed surface. During the two years of operation of Cosmo Sky Med, several images collected in stripmap, pingpong and scansar mode, both over sea and terrain and sea are analyzed and discussed by using simultaneous measurements collected by operational and research weather radar.

Hydrometeor classification for X-band dual polarization radar on-board civil aircrafts

Polarimetric techniques applied to radars on-board civil aircraft can improve the estimation of risk zones due to dangerous weather during flight. Usually, X-band weather radars are installed at the nose of civil aircrafts. This band is affected by strong attenuation in case of intense precipitation (liquid or mixed phase). The current systems do not compensate backscattered power measurements for attenuation caused by propagation through precipitation, while dual-polarization radars are able to compensate effectively this source of error and to discriminate hydrometeors. In this work, a classification algorithm based on support vector machines (SVM) is proposed. Training is driven by the output of a Fuzzy Logic (FL) classification algorithm (typical classification approach used for ground-based weather radar). SVM high performance in terms of time processing and its flexibility of configuration using all type of inputs variables are important characteristics to be included in some avionic specific equipment, such as the Electronic Flight Bag (EFB). Two datasets have been used to test the SVM classification algorithm. The first dataset is composed of simulated radar polarimetric observations at X-band and the second one is composed of actual dual-polarization radar measurements collected during the Special Observation Period (SOP) 1.1 of HYdrological cycle in MEditerranean EXperiment (Hymex) campaign by the C-band Doppler dual-polarization weather radar (Polar 55C) installed at ISAC-CNR in Rome. Good performance are obtained for SVM classificator. The comparison with FL output shows a good agreement (up to 90%) both in qualitative comparison maps by maps and using a quantitative approach which metric is based on the confusion matrix.

Use of the constellation of PMW radiometers in the GPM ERA for heavy precipitation event monitoring and analysis during fall 2014 in Italy

In this study, precipitation retrievals exploiting the available overpasses of passive microwave (PMW) cross-track and conically scanning radiometers in the GPM era are used to monitor the evolution of heavy precipitation systems occurred during the fall 2014 in Italy. Two different physically-based retrieval algorithms (CDRD for SSMIS and PNPR for AMSU/MHS and ATMS) are used in conjunction with official NASA/JAXA GPM instantaneous precipitation products (for AMSR-2 and GMI). The comparison with dual-polarization radar observations at ground evidences the ability of the different sensors to identify different precipitation areas and regimes. This is particularly relevant in presence of complex orography, often found in proximity of coastal areas for the analyzed cases. Analysis of the accuracy and consistency of the retrievals is carried out taking into account the different spatial resolution and viewing geometry of the different radiometers and the different approaches used for the precipitation retrieval.

Ground-Based Weather Radar to Investigate Thunderstorms

Weather radars are considered an essential tool to identify and analyze rapidly evolving phenomenon like thunderstorms that are related to threats like high precipitation rates or wind speeds. Depending on the characteristics of radar, different features of a thunderstorm can be detected to highlight important characteristics such its severity, trajectory evolution and particle type distribution within the storm cloud. This chapter describes how different radar measurements (reflectivity, Doppler measurements, and dual-polarization measurements) are usually exploited by radar experts to identify important characteristics of such phenomena. In particular, dual-polarization weather radar allows to identify and quantify the presence of graupel particles that can be present within a cumulonimbus and can be associated with electrical activity, which is the unique characteristic of a thunderstorm.

C/S algorithm based on properties of dual-polarization radar measurements derived from disdrometer data

The paper proposes a convective/stratiform (C/S) classification algorithm based on dual-polarization radar measurements obtained from disdrometer measurements through an electromagnetic scattering/extinction model. The drop size distributions, collected by a 2D video disdrometer (2DVD) installed in Rome during HyMeX SOP1, have been used to define the algorithm, and the C-band radar measurements, collected by a Polar 55C, have been analyzed to assess the performance of the proposed method.