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Active remote sensing of volcanic plumes: models, algorithms and applications
No full textMy Research focuses on Remote Sensing of volcanic ash clouds. Volcanic eruptions represent a serious threat to human safety that might have a considerable impact on global economic activities. Prevention and mitigation of risk related to volcanic activity needs comprehension and better knowledge of eject materials. The different data derived from observation of ground-based and satellite-based sensors have been used to train the prediction models. Firstly I have properly adapted and extended the "T_Matrix code”(Michshenko et al., 1996a-1996b-1998-200), which implements the method EBCM (Extended Boundary Condition Method) and represents the theoretical solution to the problem of scattering by non-spherical particles, to include the optical wavelength of NIR, VIS and UV. The ash particles main electromagnetic and microphysical parameters, implemented in the simulator HAPESS (Hydro Ash Particle Ensemble Scatter Simulator), allowed creating a Monte Carlo generation of Radar and Lidar synthetic signatures used to perform the physically-oriented algorithm VASR. The latter is a crucial technique to retrieve information about volcanic source parameters, and it basically consists in two main sub-steps: classification and estimation. Applying Maximum A Posteriori Probability (MAP) criterion on radar/lidar measured observables, is then possible to make a classification of ash category and then applying the regressive power-laws, previously calculated, we can estimate the ash concentration, the number-weighted mean diameter and other volcanic source parameters used to train the ash plume dispersal models. If we use a Maximum Likelihood (ML) approach to retrieve these volcanic parameters, we need only to select the useful values corresponding to specific criteria. The physical-based methodology VASR has been extended to ingest different ash particles kinds, such as mixture and coexistence between meteorological and volcanic-origin particles. In this research work we will see the potential of this method and the innovative aspect of this methodology, such as the Mass Flow Rate (MFR) estimation; it opens new possibilities in the applied research field to volcanic eruption study and the resulting impact in the atmosphere.
The first case study considered is related to the ground-based observation of volcanic ash plume, erupted from the Eyjafjallajökull volcano on May 2010. We have used different sensor data to estimate the concentration, top plume altitude and MFR. Some volcanic source parameters derived from radar data show a good agreement with estimations derived from other models and methodologies. When the different sensor data were available at the same time, we have combined them with our information in order to validate and corroborate the validity of our technique.
Another case analysed is related to Grimsvötn eruption 2011. In this case we have analysed only a short time series of data, in order to obtain the MFR estimates and related MFR profiles, and to verify, also in this case, a good agreement of MFR estimations derived by the radar and the 1D model.
The Holuhraun case analysed is the more interesting case because it was characterized by turbulent phenomena happened, such as dust devils, due both to particular environmental conditions and to the situ morphology. In this case, different sensors have observed the same ash plume. Both radars estimations show the same ash class and the similar occurrence. Considering the different sensitivity of two sensors also the volcanic source parameters show a good agreement between them. The particular environmental condition we allow to suppose also the mixed-phase ash classes.
The analysed Etna cases, using the scanning lidar system, show how this sensor can be complementary to radar systems. The lidar observations of the smallest dispersed ash particle in the atmosphere can help finding the main microphysical ash features and the areas characterized by a specific mass concentration of the smallest ash particles. This information may help quantifying the impact that ash emissions have on aviation safety to prevent the flights in the areas of high ash contamination (2x10-4g/m3) in compliance with the International Civil Aviation Organization directives [International Civil Aviation Organization (ICAO), 2010]. This case study, starting from the inter-comparison between the VALR algorithm and ash dispersal model, highlights a 25% smaller ash contaminated area considering different dimensional ash particles; this allows us to define a 25% security margin in the interdicted area in comparison with the area obtained applying the ash dispersal model.
The last case analysed is related to Calbuco eruption on April 2015. This strong and very tephra-rich eruption generated a bigger dispersed ash plume observed by different sensors on board of some satellite platforms carrying various active and passive remote sensors. In this particular case we have used the brightness temperature data derived by VIS-IR radiometer of GOES-13 (Geostationary Operational Environmental Satellite), AVHRR (Advanced Very High Resolution Radiometer) radiometer on board of National Oceanic and Atmospheric Administration's (NOAA's) Polar Orbiting Environmental Satellites (POES) satellites and VIIRS Visible Infrared Imaging Radiometer Suite radiometers on board of S-NPP (Suomi National Polar-orbiting Partnership) to perform only a firstly quantitative analysis, using the known brightness temperature difference BTD between the optical band, in order to discriminate between the ash and meteorological cloud. The CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar and IIR (Imaging Infrared Radiometer) radiometer on board of CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite overpassing at the same time as other satellite sensors confirms the presence of the ash plume, as observed by other sensors data analysis. Using the Caliop data we have classified and estimated the main ash classes detected in the plume vertical section observed, confirming the presence of dispersed very small ash particles. This case is very interesting because combining the information derived by satellite sensors, such as the extension of ash plume detected with the vertical structure derived by Caliop, we can have a good information about the 3D structure of dispersed ash plume
Potential of weather radar in estimating volcanic eruption source parameters: case study of Eyjafjallajökull volcano eruption
No full textRetrieval of tephra size spectra and mass flow rate from C-band radar during the 2010 Eyjafjallajökull eruption, Iceland
No full textThe eruption of the Eyjafjallajokull volcano in April-May 2010 was continuously monitored by the Keflavik C-band weather radar. The Keflavik 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 Eyjafjallajokull 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 Eyjafjallajokull area. VARR-retrievedMFRs 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Exploiting microwave scanning radar for monitoring Icelandic volcanic eruption source parameters
No full textThe explosive eruption at the summit of sub-glacial Ejyafjallajökull volcano in April-May 2010 was of modest size, but with a erupted ash plume reaching a 6-10 km height above the volcano vent. The ash was widely dispersed over Iceland and Europe, causing a global interruption of main air traffic and causing large economic losses. The quality of the airborne ash particle forecast in the atmosphere depends on realistic description of erupted ash dispersion and then on erupted fine ash mass rate. In this primary work, we present the validity of the use of microwave radar data to estimate mass flows rate MFR through an interesting extension of the Volcanic Ash Radar Retrieval (VARR), which uses the observables of C-band radar in Keflavik
Ground-based microwave radar and optical lidar signatures of volcanic ash plumes: models, observations and retrievals
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Precipitating cloud effects on the radar polarimetric signature at Ka band
No full textIn this work we will introduce a simulation framework developed to characterize precipitating clouds effects on spaceborne X- and Ka-Band spaceborne Synthetic Aperture Radar (SAR) systems. The work has been accomplished in the framework of an ESA project aiming at supporting instrument parametric analyses and establishing system requirements of spaceborne Ka polarimetric/interferometric radar. Preliminary results will be discussed
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