12,311 research outputs found
Inundated Area Delineation Using MODIS Data: Towards a Global Scale Geo-Database of Flood Events
The availability of global and accurate information is the primary factor affecting the possibility of planning and managing effective disaster response strategies, above all in less developed countries. The second determinant factor that avoids the full spreading of remote sensing technologies is cost-effectiveness and steadiness of results. This paper illustrates a straightforward method for rapid retrieval of inundation maps at regional and global scale by processing MODIS data with the Spectral-Temporal Principal Components Analysis and Digital Terrain Model filtering. Case studies are presented for three different vulnerable regions in developing countries struck by a severe river flood during the last year (2005, from spring to fall): India, Pakistan and Romania. For all the events studied it was obtained an overall accuracy greater than 95% and a kappa coefficient grater than 0.70, demonstrating this methodology is very accurate in mapping inundated areas. Moreover, the integration with vector data (such as roads, railways or urbanized areas) may be used to fast detect infrastructure damages at regional and global scale. This work is the first step to develop a global geo-database of flood-affected areas, a basic tool for helping public administrators in efficiently managing natural hazards. This is especially useful for less developed countries, which unfortunately suffer the heaviest damages because of the high density of population and the scarcity of prevention and rapid response strategies
Monsoon Flooding Response: a Multi-scale Approach to Water-extent Change Detection
This paper has the aim of illustrating an automatic and speditive way for retrieving inundation extent from multispectral and multitemporal satellite data, together with land-cover changes caused by flooding events, which is a fundamental issue for managing a reconstruction plan after the event. A straightforward method to map inundated areas was applied in the North-Eastern region of Bangladesh, heavily struck by monsoonal rains in September 2000. This method in based on the Principal Components Transform (PCT) of multispectral satellite data, in its Spectral-Temporal implementation, followed by logical filtering and image segmentation, in order to reach the needed coherency of the results. The use of multiresolution data (28.5-meters ground resolution Landsat-7/ETM+ and 1,100-meters ground resolution NOAA-14/AVHRR) makes possible to evaluate hazard affected areas at different scales. Comparison to RADARSAT-derived water extension maps assessed an Overall Accuracy between 86.4% (for the flood map derived with NOAA-14/AVHRR data over the whole Bangladesh) and 90.6% (for the flood map derived with Landsat-7/ETM+ data over the North-East part of the country)
Diversity, Assortment, Dissimilarity, Variety: A Study of Diversity Measures Using Low Level Features for Video Retrieval
In this paper we present a number of methods for re-ranking video search results in order to introduce diversity into the set of search results. The usefulness of these approaches is evaluated in comparison with similarity based measures, for the TRECVID 2007 collection and tasks [11]. For the MAP of the search results we find that some of our approaches perform as well as similarity based methods. We also find that some of these results can improve the P@N values for some of the lower N values. The most successful of these approaches was then implemented in an interactive search system for the TRECVID 2008 interactive search tasks. The responses from the users indicate that they find the more diverse search results extremely useful
Experiment Investigating the Connection between Weak Values and Contextuality
Weak value measurements have recently given rise to a large interest for both
the possibility of measurement amplification and the chance of further quantum
mechanics foundations investigation. In particular, a question emerged about
weak values being proof of the incompatibility between Quantum Mechanics and
Non-Contextual Hidden Variables Theories (NCHVT). A test to provide a
conclusive answer to this question was given in [M. Pusey, Phys. Rev. Lett.
113, 200401 (2014)], where a theorem was derived showing the NCHVT
incompatibility with the observation of anomalous weak values under specific
conditions. In this paper we realize this proposal, clearly pointing out the
strict connection between weak values and the contextual nature of Quantum
Mechanics.Comment: 5 pages, 4 figure
Recommended from our members
Visualisation and les simulation of cavitation cloud formation and collapse in an axisymmetric geometry
Visualisation and Large Eddy Simulations (LES) of cavitation inside the apparatus previously developed by Franc (2011) for surface erosion acceleration tests and material response monitoring are presented. The experimental flow configuration is a steady-state closed loop flow circuit where pressurised water, flowing through a cylindrical feed nozzle, is forced to turn 90° and then, move radially between two flat plates towards the exit of the device. High speed images show that cavitation is forming at the round exit of the feed nozzle. The cavitation cloud then grows in the radial direction until it reaches a maximum distance where it collapses. Due to the complexity of the flow field, direct observation of the flow structures was not possible, however vortex shedding is inferred from relevant simulations performed for the same conditions. Despite the axisymmetric geometry utilized, instantaneous pictures of cavitation indicate variations in the circumferential direction. Image post-processing has been used to characterize in more detail the phenomenon. In particular, the mean cavitation appearance and the cavity length have been estimated, showing good correlation with the erosion zone. This also coincides with the locations of the maximum values of the standard deviation of cavitation presence. The dominant frequency of the ‘large-scale’ cavitation clouds has been estimated through FFT. Cloud collapse frequencies vary almost linearly between 200 and 2000 Hz as function of the cavitation number and the downstream pressure. It seems that the increase of the Reynolds number leads to a reduction of the collapse frequency; it is believed that this effect is due to the agglomeration of vortex cavities, which causes a decrease of the apparent frequency. The results presented here can be utilized for validation of relevant cavitation erosion models which are currently under development
Efficiently Clustering Very Large Attributed Graphs
Attributed graphs model real networks by enriching their nodes with
attributes accounting for properties. Several techniques have been proposed for
partitioning these graphs into clusters that are homogeneous with respect to
both semantic attributes and to the structure of the graph. However, time and
space complexities of state of the art algorithms limit their scalability to
medium-sized graphs. We propose SToC (for Semantic-Topological Clustering), a
fast and scalable algorithm for partitioning large attributed graphs. The
approach is robust, being compatible both with categorical and with
quantitative attributes, and it is tailorable, allowing the user to weight the
semantic and topological components. Further, the approach does not require the
user to guess in advance the number of clusters. SToC relies on well known
approximation techniques such as bottom-k sketches, traditional graph-theoretic
concepts, and a new perspective on the composition of heterogeneous distance
measures. Experimental results demonstrate its ability to efficiently compute
high-quality partitions of large scale attributed graphs.Comment: This work has been published in ASONAM 2017. This version includes an
appendix with validation of our attribute model and distance function,
omitted in the converence version for lack of space. Please refer to the
published versio
High Performances Corrugated Feed Horns for Space Applications at Millimetre Wavelengths
We report on the design, fabrication and testing of a set of high performance
corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced
prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission.
The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70
GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and
by electro-formation at higher frequencies. The measured performances on side
lobes and return loss meet the stringent Planck requirements over the large
(20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape
and side lobes levels of the dual profiled designs has been demonstrated.Comment: 16 pages, 7 figures, accepted for publication in Experimental
Astronom
Planck LFI flight model feed horns
this paper is part of the Prelaunch status LFI papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jinst The Low Frequency
Instrument is optically interfaced with the ESA Planck telescope through 11
corrugated feed horns each connected to the Radiometer Chain Assembly (RCA).
This paper describes the design, the manufacturing and the testing of the
flight model feed horns. They have been designed to optimize the LFI optical
interfaces taking into account the tight mechanical requirements imposed by the
Planck focal plane layout. All the eleven units have been successfully tested
and integrated with the Ortho Mode transducers.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in JINST. IOP Publishing Ltd is not responsible for
any errors or omissions in this version of the manuscript or any version
derived from it. The definitive publisher authenticated version is available
online at 10.1088/1748-0221/4/12/T1200
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