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http://hdl.handle.net/2122/288
20150905T16:17:21Z

ANNALS OF GEOPHYSICS: AD MAJORA
http://hdl.handle.net/2122/9916
Title: ANNALS OF GEOPHYSICS: AD MAJORA
Authors: Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caprara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Chiodetti, A. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Gresta, S.; Univ Catania
Abstract: Annals of Geophysics (ISSN: 15935213; from 2010, 2037416X) is a bimonthly international journal, which publishes scientific papers in the field of geophysics sensu lato. It derives from Annali di Geofisica (ISSN: 03652556), which commenced publication in January 1948 as a quarterly periodical devoted to general geophysics, seismology, Earth magnetism, and atmospheric studies....
20131231T23:00:00Z

Volcanic plume vent conditions retrieved from infrared images: A forward and inverse modeling approach
http://hdl.handle.net/2122/9834
Title: Volcanic plume vent conditions retrieved from infrared images: A forward and inverse modeling approach
Authors: Cerminara, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Esposti Ongaro, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Valade, S.; Harris, A. J. L.
Abstract: We present a coupled fluiddynamic and electromagnetic model for volcanic ash plumes. In a forward approach, the model is able to simulate the plume dynamics from prescribed input flow conditions and generate the corresponding synthetic thermal infrared (TIR) image, allowing a comparison with fieldbased observations. An inversion procedure is then developed to retrieve vent conditions from TIR images, and to independently estimate the mass eruption rate.
The adopted fluiddynamic model is based on a onedimensional, stationary description of a selfsimilar turbulent plume, for which an asymptotic analytical solution is obtained. The electromagnetic emission/absorption model is based on Schwarzschild's equation and on Mie's theory for disperse particles, and we assume that particles are coarser than the radiation wavelength (about 10 μm) and that scattering is negligible. In the inversion procedure, model parameter space is sampled to find the optimal set of input conditions which minimizes the difference between the experimental and the synthetic image.
Application of the inversion procedure to an ash plume at Santiaguito (Santa Maria volcano, Guatemala) has allowed us to retrieve the main plume input parameters, namely mass flow rate, initial radius, velocity, temperature, gas mass ratio, entrainment coefficient and their related uncertainty. Moreover, by coupling with the electromagnetic model we have been able to obtain a reliable estimate of the equivalent Sauter diameter of the total particle size distribution.
The presented method is general and, in principle, can be applied to the spatial distribution of particle concentration and temperature obtained by any fluiddynamic model, either integral or multidimensional, stationary or timedependent, single or multiphase. The method discussed here is fast and robust, thus indicating potential for applications to realtime estimation of ash mass flux and particle size distribution, which is crucial for modelbased forecasts of the volcanic ash dispersal process.
20141231T23:00:00Z

Modeling the dynamics of a geothermal reservoir fed by gravity driven flow through overstanding saturated rocks
http://hdl.handle.net/2122/9781
Title: Modeling the dynamics of a geothermal reservoir fed by gravity driven flow through overstanding saturated rocks
Authors: Cerminara, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Fasano, A.
Abstract: We formulate a mathematical model for a geothermal basin with an idealized geometry characterized by: (1) radial symmetry around an extracting well (or a cluster of wells), (2) a relatively thin horizontal fractured layer lying underneath a low permeability, low porosity rock layer, saturated with water. Vaporization is allowed only at the boundary of the extracting well (or well cluster). The model is based on the assumption that the flow from the reservoir to the well is fed by a gravity driven flow through the overstanding rocks. Despite the various simplifying assumptions, the resulting mathematical problem is considerably difficult also because we consider the effect of thermal expansion and thermal variation of viscosity. Though there is no evidence that the assumed configuration of the basin approaches the structure of a known geothermal field, the results obtained match with surprising accuracy the data of a specific field in the Mt. Amiata area (data kindly provided by ENEL Green Power through Tuscany Region).
20120329T22:00:00Z

Disperse TwoPhase Flows, with Applications to Geophysical Problems
http://hdl.handle.net/2122/9780
Title: Disperse TwoPhase Flows, with Applications to Geophysical Problems
Authors: Berselli, L. C.; Università di Pisa; Cerminara, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Iliescu, T.
Abstract: In this paper, we study the motion of a fluid with several dispersed particles whose concentration is very small (smaller than 103), with possible applications to problems coming from geophysics, meteorology, and oceanography. We consider a very dilute suspension of heavy particles in a quasiincompressible fluid (low Mach number). In our case, the Stokes number is small and—as pointed out in the theory of multiphase turbulence—we can use an Eulerian model instead of a Lagrangian one. The assumption of low concentration allows us to disregard particle–particle interactions, but we take into account the effect of particles on the fluid (twoway coupling). In this way, we can study the physical effect of particles’ inertia (and not only passive tracers), with a model similar to the Boussinesq equations. The resulting model is used in both direct numerical simulations and large eddy simulations of a dambreak (lockexchange) problem, which is a wellknown academic test case. © 2014, Springer Basel.
20131231T23:00:00Z

Sill intrusion as a source mechanism of unrest at volcanic calderas
http://hdl.handle.net/2122/9767
Title: Sill intrusion as a source mechanism of unrest at volcanic calderas
Authors: Macedonio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Giudicepietro, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; D'Auria, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Martini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia
Abstract: The interpretation of dynamic processes that occur in volcanic calderas is not simple. The ground deformations and the local seismicity, which in other volcanic contexts are usually regarded as precursors to eruption, in caldera environment in many cases are not followed by any eruption. We formulate a general hypothesis that can explain these behaviors. Our hypothesis is that the intrusion of a sill can be responsible for the dynamics observed during unrest at calderas. In order to investigate the reliability of this hypothesis, we developed a dynamic model of sill intrusion in a shallow volcanic environment. In our model, the sill, fed by a deeper magma reservoir, intrudes below a horizontal elastic plate, representing the overlying rocks, and expands with axisymmetric geometry. The model is based on the numerical solution of the equation for the elastic plate, coupled with a NavierStokes equation for simulating the dynamics of the sill intrusion. We performed a number of simulations, with the objective of showing the main features of the model. In the experiments, when the feeding process stops, the vertical movement reverses its trend and the area of maximum uplift undergoes subsidence. Under certain conditions the subsidence can occur even during the intrusion of the sill. The stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front. The features predicted by the model are consistent with many observations carried out on different calderas as reported in the scientific literature.
20140501T22:00:00Z

Joining multiple AEM datasets to improve accuracy, cross calibration and derived products: The Spiritwood VTEM and AeroTEM case study
http://hdl.handle.net/2122/9456
Title: Joining multiple AEM datasets to improve accuracy, cross calibration and derived products: The Spiritwood VTEM and AeroTEM case study
Authors: Sapia, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Viezzoli, A.; Aarhus Geophysics Aps; Oldenborger, G.; Geological Survey of Canada
Abstract: Airborne timedomain electromagnetic methods (AEM) are useful for hydrogeological mapping
due to their rapid and extensive spatial coverage and high correlation between measured magnetic
fields, electrical conductivity, and relevant hydrogeological parameters. However, AEM data, preprocessing
and modelling procedures can suffer from inaccuracies that may dramatically affect the
final interpretation. We demonstrate the importance and the benefits of advanced data processing
for two AEM datasets (AeroTEM III and VTEM) collected over the Spiritwood buried valley aquifer
in southern Manitoba, Canada. Earlytime data gates are identified as having significant flightdependent
signal bias that reflects survey flights and flight lines. These data are removed from
inversions along with late time data gates contaminated by apparently random noise. In conjunction
with supporting information, the lessextensive, but broaderband VTEM data are used to construct
an electrical reference model. The reference model is subsequently used to calibrate the AeroTEM
dataset via forward modelling for coincident soundings. The procedure produces calibration factors
that we apply to AeroTEM data over the entire survey domain. Inversion of the calibrated data
results in improved data fits, particularly at early times, but some flightline artefacts remain.
Residual striping between adjacent flights is corrected by including a mean empirical amplitude
correction factor within the spatially constrained inversion scheme. Finally, the AeroTEM and
VTEM data are combined in a joint inversion. Results confirm consistency between the two different
AEM datasets and the recovered models. On the contrary, joint inversion of unprocessed or
uncalibrated AEM datasets results in erroneous resistivity models which, in turn, can result in an
inappropriate hydrogeological interpretation of the study area.
20141231T23:00:00Z

A second order finitedifference ghostpoint method for elasticity problems on unbounded domains with applications to volcanology
http://hdl.handle.net/2122/9375
Title: A second order finitedifference ghostpoint method for elasticity problems on unbounded domains with applications to volcanology
Authors: Coco, A.; Bristol University; Currenti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Del Negro, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Russo, G.; Università di Catania
Abstract: We propose a novel nitedi erence approach for the numerical solution of linear elasticity problems in
arbitrary unbounded domains. The method is an extension of a recently proposed ghostpoint method
for the Poisson equation on bounded domains with arbitrary boundary conditions (Coco, Russo, JCP,
2013) to the case of the CauchyNavier equations on unbounded domains. The technique is based on
a smooth coordinate transformation, which maps an unbounded domain into a unit square. Arbitrary
geometries are de ned by suitable levelset functions. The equations are discretized by classical ninepoint
stencil on interior points, while boundary conditions and high order reconstructions are used to
de ne the eld variable at ghostpoint, which are grid nodes external to the domain with a neighbor
inside the domain. The approach is then adopted to solve elasticity problems applied to volcanology
for computing the displacement caused by an underground pressure source. The method is suitable
to treat problems in which the geometry of the source often changes (explore the e ects of di erent
scenarios, or solve inverse problems in which the geometry itself is part of the unknown), since it
does not require complex remeshing when the geometry is modi ed. Several numerical tests are
performed, which asses the e ectiveness of the present approach.
Keywords: Linear Elasticity, CauchyNavier equations, ground deformation, unbounded domain,
coordinate transformation method, Cartesian grid, Ghost points, Levelset methods
20131231T23:00:00Z

Correction’s method of the electron density model in ionosphere by ray tracing techniques
http://hdl.handle.net/2122/9340
Title: Correction’s method of the electron density model in ionosphere by ray tracing techniques
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Università Sapienza, Dipartimento di Fisica, p.le Aldo Moro 2, I00185 Rome, Italy; Baskaradas, J. A.; School of Electrical & Electronics Engineering, Shanmugha Arts, Science, Technology & Research Academy (SASTRA) University, Tirumalaisamudram, Thanjavur, 613 401 Tamilnadu, India
Abstract: When applying the ray tracing in ionospheric propagation, the electron density modelling is the main input of the algorithm, since phase refractive index strongly depends on it. Also the magnetic field and frequency collision modelling have their importance, the former as responsible for the azimuth angle deviation of the vertical plane containing the radio wave, the latter for the evaluation of the absorption of the wave. Anyway, the electron density distribution is strongly dominant when one wants to evaluate the group delay time characterizing the ionospheric propagation. From the group delay time, azimuth and elevation angles it is possible to determine the point of arrival of the radio wave when it reaches the Earth surface. Moreover, the procedure to establish the target (T) position is one of the essential steps in the Over The Horizon Radar (OTHR) techniques which require the correct knowledge of the electron density distribution. The group delay time generally gives rough information of the ground range, which depends on the exact path of the radio wave in the ionosphere. This paper focuses on the lead role that is played by the variation of the electron density grid into the ray tracing algorithm, which is correlated to the change of the electron content along the ionospheric ray path, for obtaining a ray tracing as much reliable as possible. In many cases of practical interest, the group delay time depends on the geometric length and the electron content of the ray path. The issue is faced theoretically, and a simple analytical relation, between the variation of the electron content along the path and the difference in time between the group delays, calculated and measured, both in the ionosphere and in the vacuum, is obtained and discussed. An example of how an oblique radio link can be improved by varying the electron density grid is also shown and discussed.
20150314T23:00:00Z

Ray theory formulation and ray tracing method. Application in ionospheric propagation
http://hdl.handle.net/2122/9139
Title: Ray theory formulation and ray tracing method. Application in ionospheric propagation
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Dipartimento di Fisica, Università “Sapienza”, p.le Aldo Moro 2, 00185 Roma, Italia
Abstract: This work will lead to ray theory and ray tracing formulation. To deal with this problem the theory of classical geometrical optics is presented, and applications to ionospheric propagation will be described. This provides useful theoretical basis for scientists involved in research on radio propagation in inhomogeneous anisotropic media, especially in a magnetoplasma. Application in high frequencies (HF) radio propagation, radio communication, overthehorizonradar (OTHR) coordinate registration and related homing techniques for direction finding of HF wave, all rely on ray tracing computational algorithm. In this theory the formulation of the canonical, or Hamiltonian, equations related to the ray, which allow calculating the wave direction of propagation in a continuous, inhomogeneous and anisotropic medium with minor gradient, will be dealt. At least six Hamilton’s equations will be written both in Cartesian and spherical coordinates in the simplest way. These will be achieved by introducing the refractive surface index equations and the ray surface equations in an appropriate freedimensional space. By the combination of these equations even the Fermat’s principle will be derived to give more generality to the formulation of ray theory. It will be shown that the canonical equations are dependent on a constant quantity H and the Cartesian coordinates and components of wave vector along the ray path. These quantities respectively indicated as ri(τ), pi(τ) are dependent on the parameter τ, that must increase monotonically along the path. Effectively, the procedure described above is the ray tracing formulation. In ray tracing computational techniques, the most convenient Hamiltonian describing the medium can be adopted, and the simplest way to choose properly H will be discussed. Finally, a system of equations, which can be numerically solved, is generated.
20141022T22:00:00Z

The calculation of ionospheric absorption with modern computers
http://hdl.handle.net/2122/9104
Title: The calculation of ionospheric absorption with modern computers
Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: New outcomes are proposed for ionospheric absorption starting from the AppletonHartree formula, in its complete form. The range of applicability is discussed for the approximate formulae, which are usually employed in the calculation of nondeviative absorption coefficient. These results were achieved by performing a more refined approximation that is valid under quasilongitudinal (QL) propagation conditions. The more refined QL approximation and the usually employed nondeviative absorption are compared with that derived from a complete formulation. Their expressions, nothing complicated, can usefully be implemented in a software program running on modern computers. Moreover, the importance of considering Booker’s rule is highlighted. A radio link of ground range D = 1000 km was also simulated using ray tracing for a sample daytime ionosphere. Finally, some estimations of the integrated absorption for the radio link considered are provided for different frequencies.
20141014T22:00:00Z