Luigi Mereu

Retrieval of Tephra Size Spectra and Mass Flow Rate From C-Band Radar During the 2010 Eyjafjallajökull Eruption, Iceland

The eruption of the Eyjafjallajökull volcano in April-May 2010 was continuously monitored by the Keflavík C-band weather radar. The Keflavík radar is located at a distance of about 156 km from the volcano vent, and it has sensitivity of about -5 dBZ at 2-km range resolution over the volcanic area. The time series of radar volume data, which was available every 5 min, is quantitatively analyzed by using the Volcanic Ash Radar Retrieval (VARR) technique. The latter is a physically based methodology that is applied to estimate ash-fall rate and mass concentration within each radar volume. The VARR methodology is here extended, with respect to the previous formulation, to provide an approximate estimate of both mean particle diameter and airborne tephra particle size distribution under some assumptions. Deposited tephra at ground is also extrapolated together with an estimate of the magma mass flow rate (MFR) at the volcano vent, derived from the implementation of the mass continuity equation in the radar reference system. The VARR-based retrievals are compared with those derived from a direct tephra sampling at the ground, experimentally carried out in terms of ash grain size and loading during the Eyjafjallajökull eruption activity on May 5-7, 2010. VARR-based particle diameter estimates may suggest that a sorting of airborne particles during the downwind transport is taking place without observing aggregation processes during the ash fall. VARR-derived daily ash mass loadings in the period between April 14 and May 10 are also evaluated with respect to integrated ground and model-based data in the Eyjafjallajökull area. VARR-retrieved MFRs are finally compared with corresponding values obtained from analytical 1-D eruption models, using radar-estimated plume height and radio-sounding wind fields. A fairly good agreement is obtained, thus opening the exploitation of weather radar retrievals for volcanic eruption quantitative studies and ash dispersion model initialization.

C-band Dual-Polarization Radar Observations of a Massive Volcanic Eruption in South America

The eruption of Calbuco volcano on April 22–23, 2015 is the first volcanic eruption detected by a weather radar in South America. The detection was performed by the first domestically produced Argentinean weather radar, called RMA0 and located at Bariloche International Airport. It is a C-band Doppler dual-polarization system, manufactured by INVAP S.E. as a part of the new radar network of Argentina. The aim of this study is to present analysis of the time evolution of the structure of the volcanic plume using polarimetric observables. In order to explore the potential of this new data set for the analysis of the Calbuco volcano eruption column and dispersed ash cloud, synthetic backscattering signatures at C-band have been simulated and used to set up a threshold-based algorithm for tephra-type classification. An evaluation of lightning activity and its relationships with the volcanic particle spatial distribution and attendant polarimetric radar signatures are also discussed.

Hydrometeor scattering and stochastic modeling for free-space optical channel characterization

Free space communications, using optical carriers (Free Space Optics, FSO) technology, ensure high data rates, with relatively low error rates, low power consumption and inherent security. However, FSO links are quite sensitive to atmospheric conditions. Fog droplets, but also raindrops and snowflakes, may introduce severe path attenuation which drastically reduces the channel availability. A parametric model to simulate droplets scattering effects on FSO links (from visible to near infrared wavelengths) is proposed in terms of scattering coefficients, albedo factor and asymmetry coefficient as function of the particle water content. Both single and multiple scattering effects are shown and discussed. A prototype of a stochastic time series generator of FSO rain attenuation is also presented.

Near-Real-Time Detection of Tephra Eruption Onset and Mass Flow Rate Using Microwave Weather Radar and Infrasonic Arrays

During an eruptive event, the near-real-time monitoring of volcanic explosion onset and its mass flow rate (MFR) is a key factor to predict ash plume dispersion and to mitigate risk to air traffic. Microwave (MW) weather radars have proved to be a fundamental instrument to derive eruptive source parameters. We extend this capability to include an early-warning detection scheme within the overall volcanic ash radar retrieval methodology. This scheme, called the volcanic ash detection (VAD) algorithm, is based on a hybrid technique using both fuzzy logic and conditional probability. Examples of VAD applications are shown for some case studies, including the Icelandic Grímsvötn eruption in 2011, the Eyjafjallajökull eruption in 2010, and the Italian Mt. Etna volcano eruption in 2013. Estimates of the eruption onset from the radar-based VAD module are compared with infrasonic array data. One-dimensional numerical simulations and analytical model estimates of MFR are also discussed and intercompared with sensor-based retrievals. Results confirm in all cases the potential of MW weather radar for ash plume monitoring in near real time and its complementarity with infrasonic array for early-warning system design.

Atmospheric precipitation impact on synthetic aperture radar imagery: Numerical model at X and KA bands

Recent spaceborne polarimetric Synthetic Aperture Radars (SARs) enable the complete characterization of target scattering and extinction properties. Several missions are operating at X band while there are plans and analyses for systems operating at higher frequencies, such as Ka band. Systems operating at these frequencies have interesting and distinctive applications in the field of geosciences such as Cartography, Surface deformation detection, Forest cover mapping and many others. However, the detected ground surface response can be affected by atmospheric effects in both signal amplitude and phase, especially in presence of atmospheric precipitations. In this work we will introduce a simulation framework developed to characterize how precipitating clouds affect spaceborne X- and Ka-band SARs systems. The proposed framework is able to simulate the polarimetric SAR ground responses in terms of Normalized Radar Cross Sections (NRCS) and complex correlation coefficient, both for realistic atmosphere-ground scenarios and for synthetic canonical ones. Some preliminary results will be shown and discussed.