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New applications and challenges of GNSS variometric approach
Full text linkGlobal Navigation Satellite Systems (GNSS) are nowadays widely used in several technical and scientific activities. Since the early stages of development (mid 1980 s), given the high level of accuracy achieved in determining the coordinates of the receiver, it became clear that the extensive deployment of GPS stations all over the world would have improved many tasks in geodesy and geodynamics.
The use of GNSS signals is now not only limited to the estimation of the receiver's position, but it has eventually become a key instrument for ionospheric and tropospheric remote sensing studies, and for soil features (GNSS reflectometry). In particular, GNSS can be used to monitor the ionosphere at different time and space scales. On a global scale, GNSS signals are used to generate Global Ionosphere Maps (GIM) by measuring the total electron content from stations located around the world. On a regional scale, the same signals can be used to detect fast ionospheric disturbances, including those generated by natural hazards, such as tsunami and earthquakes.
%For these reasons, real-time GNSS applications became particularly relevant in a number of different scientific fields.
The Variometric Approach is a processing algorithm for GNSS observations which allow a GNSS receiver to provide valuable real-time information in a stand-alone operative mode.
This approach is based on single time differences of suitable linear combinations of GNSS carrier-phase measurements, using a stand-alone GNSS receiver and standard GNSS broadcast products (orbits and clocks corrections) that are available in real-time. This thesis investigates the possibility to apply the Variometric Approach to the monitoring of the ionosphere, in order to detect in real-time ionospheric disturbances generated by tsunami.
The first chapter of this thesis will serve as a preface to define fundamental concepts that we will refer to throughout the rest of this work.
The rest of this thesis is divided into two main parts. In the first part (chapter~\ref{sec:VADASE}), we present some advances and applications of the VADASE (Variometric Approach for Displacements Analysis Standalone Engine) algorithm to estimate in real time ground velocities and displacements using stand-alone GNSS receivers. This algorithm was eventually appointed as an effective strategy to contribute to GNSS seismology. In this section we used the 2016 Meinong earthquake occurred in Taiwan as a case study and we estimated coseismic displacements and propagation properties of the surface waves in a real-time scenario using low-cost GNSS receivers.
The second part of this work (chapters \ref{sec:VARION}, \ref{sec:rtscenario}, and \ref{sec:VARIONimpementation}) is devoted to a new GNSS processing algorithm, VARION (Variometric Approach for Real-Time Ionosphere Observation), which is capable of estimating changes in the ionosphere's Total Electron Content (TEC) using stand-alone GNSS receivers in real time. In chapter~\ref{sec:rtscenario}, the effectiveness of VARION was proven on the following study cases: 2012 Haida Gwaii earthquake and tsunami event, 2015 Chile earthquake and tsunami event, 2013 U.S. East Coast meteotsunami event, and 2017 Mexico tsunami and geomagnetic storm events. Finally, some conclusions and relevant prospects for future VARION developments are outlined.
VARION may represent a significant contribution to science because the ionosphere is strongly coupled to the dynamics of the Earth's surface, neutral atmosphere, and geomagnetic field.
In particular, these ionospheric perturbations can be used to detect in real time detection atmospheric gravity waves due to tsunamis.
During the NASA funded GNSS Tsunami Early Warning System 2017 workshop held in Sendai, Japan, July 25-27 2017, the VARION algorithm was appointed as the first real-time GNSS tsunami tracking and warning system based upon NASA's Global Differential GPS system
Compensazione cinematica ed analisi spaziale delle reti di livellazione geometrica eseguite dal Catasto nella citta' di Milano
No full textPresent-day stress field in the surroundings of the Calabrian arc
No full textPresent day stress fields in the Tyrrhenian area is the results of a complex interplay of various dynamic processes
acting at various scales, either local and regional, such as Africa-Eurasia convergence and Calabrian subduction.
In order to investigate the role played by each dynamic process in driving the tectonic and geodynamic setting
of the area, we use a finite element approach applied on both a thermal model and a tectonic model. Predicted
stress and strain in the Central Mediterranean area are compared to complementary data presently available in the
area, such as geological, geophysical and geodetic data. The results of our modeling support the hypothesis that
Africa-Eurasia convergence and Calabrian subduction are the controlling mechanism of the present-day stress field
in the southernmost part of the Tyrrhenian
An application of model uncertainty statistical assessment : a case study of tectonic deformation in the Mediterranean
No full textWe apply the statistical procedure proposed by Barzaghi et al. (2014) to determine model uncertainty for the purpose of classifying different geophysical models that simulate tectonic deformation in the Mediterranean. For each predictive geophysical model, a covariance model is established based on 500 randomly chosen parameter combinations. Using the covariance function, model prediction uncertainty is derived from parameter uncertainties. Velocities predicted through geophysical models have been compared with GPS-derived velocities by means of a χ2 statistic analysis, and these results are used to classify different models by rheology. The results indicate that including the obtained model covariance within the comparative analysis facilitates the ability to discriminate among geophysical models. When this methodology is applied to analyze the tectonic deformation in the Mediterranean, models that account for granite and granulite composition in the upper and lower crust, respectively, more effectively predict the velocity field of the study area
Tectonic Deformation in the Tyrrhenian : A Novel Statistical Approach to Infer the Role of the Calabrian Arc Complex
Full text linkWe apply the statistical procedure proposed by Barzaghi et al. (2014) to determine model uncertainty
for the purpose of classifying different geophysical models that simulate tectonic deformation in the
Mediterranean. For each predictive geophysical model, a covariance model is established based on 500
randomly chosen parameter combinations. Using the covariance function, model prediction uncertainty
is derived from parameter uncertainties. Velocities predicted through geophysical models have been
compared with GPS-derived velocities by means of a 2 statistic analysis, and these results are used
to classify different models by rheology. The results indicate that including the obtained model covariance
within the comparative analysis facilitates the ability to discriminate among geophysical models.
When this methodology is applied to analyze the tectonic deformation in the Mediterranean, models that
account for granite and granulite composition in the upper and lower crust, respectively, more effectively
predict the velocity field of the study area
SISMA project – Seismic Information System for Monitoring and Alert – present-day surface tectonic stress field at the regional scale in the Tyrrhenian area
No full text
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
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