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51.
Fabio?OrianiEmail authorView authors OrcID profile Raj?Mehrotra Grégoire?Mariethoz Julien?Straubhaar Ashish?Sharma Philippe?Renard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(2):321-340
Daily rainfall is a complex signal exhibiting alternation of dry and wet states, seasonal fluctuations and an irregular behavior at multiple scales that cannot be preserved by stationary stochastic simulation models. In this paper, we try to investigate some of the strategies devoted to preserve these features by comparing two recent algorithms for stochastic rainfall simulation: the first one is the modified Markov model, belonging to the family of Markov-chain based techniques, which introduces non-stationarity in the chain parameters to preserve the long-term behavior of rainfall. The second technique is direct sampling, based on multiple-point statistics, which aims at simulating a complex statistical structure by reproducing the same data patterns found in a training data set. The two techniques are compared by first simulating a synthetic daily rainfall time-series showing a highly irregular alternation of two regimes and then a real rainfall data set. This comparison allows analyzing the efficiency of different elements characterizing the two techniques, such as the application of a variable time dependence, the adaptive kernel smoothing or the use of low-frequency rainfall covariates. The results suggest, under different data availability scenarios, which of these elements are more appropriate to represent the rainfall amount probability distribution at different scales, the annual seasonality, the dry-wet temporal pattern, and the persistence of the rainfall events. 相似文献
52.
Tobias Dürig Fabio Dioguardi Ralf Büttner Pierfrancesco Dellino Daniela Mele Bernd Zimanowski 《Bulletin of Volcanology》2012,74(4):895-902
Brittle magmatic fragmentation plays a crucial role in explosive eruptions. It represents the starting point of hazardous
explosive events that can affect large areas surrounding erupting volcanoes. Knowing the initial energy released during this
fragmentation process is fundamental for the understanding of the subsequent dynamics of the eruptive gas-particle mixture
and consequently for the forecasting of the erupting column’s behavior. The specific kinetic energy (SKE) of the particles
quantifies the initial velocity shortly after the fragmentation and is therefore a necessary variable to model the gas-particle
conduit flow and eruptive column regime. In this paper, we present a new method for its determination based on fragmentation
experiments and identification of the timings of energy release. The results obtained on compositions representative for basaltic
and phonolitic melts show a direct dependence on magma material properties: poorly vesiculated basaltic melts from Stromboli
show the highest SKE values ranging from 7.3 to 11.8 kJ/kg, while experiments with highly vesiculated samples from Stromboli
and Vesuvius result in lower SKE values (3.1 to 3.8 kJ/kg). The described methodology presents a useful tool for quantitative
estimation of the kinetic energy release of magmatic fragmentation processes, which can contribute to the improvement of hazard
assessment. 相似文献
53.
This paper addresses oil spill detection from remotely sensed optical images. In particular, it focuses on the automatic classification
of regions of interest (ROIs) in two classes, namely oil spills or look-alikes. Candidate regions and the corresponding boundaries
have been manually identified from full resolution Moderate Resolution Imaging Spectroradiometer images, related to the Mediterranean
Sea over the years 2008 and 2009. Then, a set of features has been extracted from each ROI, allowing to formulate the oil
spill detection problem as a two-class classification task on the provided regions (i.e. using a supervised learning strategy).
Since ROI classification is challenging, some desired characteristics for the classification algorithm are first identified,
such as accuracy, robustness, etc. Then, a solution (called SVME) is provided: it is based on an ensemble of incremental/decremental
cost-oriented Support Vector Machines, aggregated with the Receiving Operating Characteristic (ROC) convex hull method in
the ROC space. Such a solution addresses all the desired characteristics. Finally, the results obtained on the collected dataset
are shown. The importance of this study is the devising of a powerful classification technique that may have an impact on
optical oil spill detection from space, especially if fused with satellite synthetic aperture radar data. Moreover, it is
shown how the proposed system can be used as a decision support tool, to help a junior operator in making more reliable detections. 相似文献
54.
Domínguez Jaime Suárez Gerardo Gorbatov Alexei Segura Fabio 《Journal of Seismology》2021,25(6):1427-1439
Journal of Seismology - A three-dimensional tomographic image of the seismic velocity structure in the crust and upper mantle of northwestern Nicaragua was performed using the back-projection... 相似文献
55.
Near-seabed (<50 m) sediments were studied throughout the Irish sector of the Rockall Trough (ca. 123,000 km2) based on a combined analysis of shallow seismic (3.5 kHz) and multibeam swath data acquired by the Irish National Seabed Survey and reprocessed here at higher resolution. The detailed identification of seven acoustic facies served to classify the Rockall Trough into six main sedimentary provinces, incorporating the well-known Feni Drift, Donegal-Barra Fan and Rockall Bank mass flow. In the northern part of the study area, extensive mass transport deposits from both flanks of the trough are the dominant depositional features. Debris flow deposits formed by ice streaming of the British-Irish ice sheet characterise most of the Donegal-Barra Fan, whereas turbidite deposition occurs towards the toe of the fan. On the western margin of the trough, the post-glacial Rockall Bank mass flow deposit displays a rough topography with no acoustic penetration. Several failure scarps are visible on the flank of the bank where the mass flow originated, and pass downslope into large sediment lobes and smaller debris flow deposits. Smaller-scale mass transport deposits were also discovered close to some canyons indenting the eastern slope. High seismic penetration characterises the Feni contourite drift deposit, and precise mapping of its geographical extent shows that it is considerably wider than previously reported. The sediment waves that drape this drift are interpreted as predominantly relict features, and their varied geometry suggests a complex oceanographic regime. In the deeper part of the trough, the data reveal novel evidence of the widespread occurrence (about 12,000 km2) of distinct seismic and backscatter signatures indicating the possible presence of fluid escape structures within fine-grained sediments of mixed contouritic, hemipelagic and turbiditic origin. Sediment overloading and increased pore pressure resulting from extensive mass wasting to the north of the area is a likely cause of dewatering-rooted fluid migration towards the seabed, but further investigations are required to confirm the nature and origin of such fluids in the Rockall Trough. 相似文献
56.
We present a new finite element (FE) method for magnetotelluric modelling of three-dimensional conductivity structures. Maxwell's equations are treated as a system of first-order partial differential equations for the secondary fields. Absorbing boundary conditions are introduced, minimizing undesired boundary effects and allowing the use of small computational domains. The numerical algorithm presented here is an iterative, domain decomposition procedure employing a nonconforming FE space. It does not use global matrices, therefore allowing the modellization of large and complicated structures. The algorithm is naturally parallellizable, and we show results obtained in the IBM SP2 parallel supercomputer at Purdue University. The accuracy of the numerical method is verified by checking the computed solutions with the results of COMMEMI, the international project on the comparison of modelling methods for electromagnetic induction. 相似文献
57.
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59.
Jesús López H. Fabio Bresolin Elena Terlevich Roberto Terlevich Daniel Rosa-González 《Astrophysics and Space Science》2009,324(2-4):351-354
We present preliminary results obtained from integral-field (IFU) data of the giant extragalactic Hii region NGC5461, located in a spiral arm (RA=14h03m41.4s, dec=+54°19′05″) of M101. The spatial and spectral information obtained with IFUs allows us to decompose the Hii region and analyze it at high resolution. 相似文献
60.
A TRACE field of view well inside the solar disk shows very well defined large loops, likely to be very inclined to the solar
surface. On the other hand there is little evidence of large loops perpendicular to the solar surface. We show that this does
not mean that most large loops have such large inclination but that perpendicular loops are much less visible to TRACE, because
of density stratification. We quantitatively evaluate this effect by modeling in detail loops with different inclinations. 相似文献