478 research outputs found
Scale Object Selection (SOS) through a hierarchical segmentation by a multi-spectral per-pixel classification
International audienceIn high resolution multispectral optical data, the spatial detail of the images are generally smaller than the dimensions of objects, and often the spectral signature of pixels is not directly representative of classes we are interested in. Thus, taking into account the relations between groups of pixels becomes increasingly important, making objectÂoriented approaches preferable. In this work several scales of detail within an image are considered through a hierarchical segmentation approach, while the spectral information content of each pixel is accounted for by a perÂpixel classification. The selection of the most suitable spatial scale for each class is obtained by merging the hierarchical segmentation and the perÂpixel classification through the Scale Object Selection (SOS) algorithm. The SOS algorithm starts processing data from the highest level of the hierarchical segmentation, which has the least amount of spatial detail, down to the last segmentation map. At each segmentation level, objects are assigned to a specific class whenever the percentage of pixels belonging to the latter, according to a pixelÂbased procedure, exceeds a predefined threshold, thereby automatically selecting the most appropriate spatial scale for the classification of each object. We apply our method to multispectral, panchromatic and panÂsharpened QuickBird images
Current geodetic deformation of the Colli Albani volcano: a review
The quiescent Colli Albano volcano is presently characterised by moderate intensity earthquakes,
seismic swarms, gas emissions and ongoing uplift that reflects the current evidences of its residual
activity. An uplift of ~30 cm over the last 43 years was recently detected by levelling surveys
performed in the time span 1950-1993 along a levelling line that crosses the highest elevation area
of the western flank of the volcano. Space based GPS and Synthetic Aperture Radar Interferometry
geodetic observations confirm that this uplift is distributed in a wide area around the craters of
Albano and Nemi, where the most recent volcanic activity occurred. GPS data from continuous
monitoring stations indicate that both horizontal and vertical deformations do occur and that can be
addressed to a shallow magmatic source. All the geodetic observations are in agreement and
highlight that the Colli Albani is still a potentially active volcano. Being located in a densely
populated area close to Rome, the volcano should deserve the same monitoring and hazard
assessment effort of any active volcano within urbanized areas. Here we review the geodetic results
obtained during the last decades for the Colli Albani volcano
Movements detection of deep seated gravitational slope deformations by means of InSAR data and photogeological interpretation: northern Sicily case study
We investigated the northern-central portion of Sicily region (southern Italy) using aerial photographs and Synthetic Aperture Radar (SAR) data obtained by ERS1 and ERS2 satellites. This area shows a geological-structural setting generated by the tectonic superposition of Apenninic-Maghrebian carbonatic structures on terrigenous deposits. Such a structural setting favoured the development of large-scale gravity driven phenomena (known in the geological literature as deep-seated gravitational slope deformations) that are mostly responsible for the landscape evolution of the whole area. Morphological evidences such as landslides, sacking or rock-flow, lateral spread and block slide can be detected from photogeological analysis. In order to understand the temporal behaviour and spatial distribution of such deformations we applied the interferometric SAR (InSAR) technique. Interferograms show fringe patterns spatially coinciding with some of the large-scale gravitative phenomena previously identified by means of aerialphoto analysis. The comparison between photogeological data and InSAR results allows delimiting the active sectors in the study area
The case of the 2005 Kashmir earthquake
The use of Very High Resolution (VHR) satellite
panchromatic image is nowadays an effective tool to
detect and investigate surface effects of natural disasters.
We specifically examined the capabilities of VHR images
to analyse earthquake features and detect changes based on
the combination of visual inspection and automatic classification
tools. In particular, we have used Quickbird (0.6m
spatial resolution) images for detecting the three main coseismic
surface features: damages, ruptures and landslides.
The present approach has been applied to the 8 October 2005,
Mw7.6 Kashmir, Pakistan, earthquake. We have focused our
study in and around the main urban areas hit by the above
earthquake specifically at Muzaffarabad and Balakot towns.
The automatic classification techniques provided the best results
wherever dealing with the damage to man-made structures
and landslides. On the other hand, the visual inspection
method demonstrated in addressing the identification of
rupture traces and associated features. The synoptic view
(concerning landslide, more than 190 millions of pixels have
been automatically classified), the spatiotemporal sampling
and the fast automatic damage detection using satellite images
provided a reliable contribution to the prompt response
during natural disaster and for the evaluation of seismic hazard
as well
Seismic Source Quantitative Parameters Retrieval from InSAR Data and Neural Networks
The basic idea of this thesis is to exploit the capabilities of neural networks in a very new
framework: the quantitative modelling of the seismic source and the interferogram inversion for
retrieving its geometric parameters. The problem can be sum up as follows. When a moderateto-
strong earthquake occurs we can apply SAR Interferometry (InSAR) technique to compute a
differential interferogram. The latter is used to detect and measure the surface displacement
field. The earthquake has been generated by an active, seismogenic, fault having its own specific
geometry. Therefore each differential interferogram contains the information concerning the
geometry of the seismic source the earthquake comes from; its shape and size, the number of
fringes, the lobe orientation and number are the main features of the surface effects field. Two
problems have been analysed in this work. The first is the identification of the seismic source
mechanism. The second is a typical inversion exercise concerning the fault plane parameter. To
perform both exercises of the seismic fault a huge number of synthetic interferograms has been
computed. Each of them is generated by a different combination of such geometric parameters.
As far as the retrieval of the geometric parameters is concerned an artificial neural network has
been properly generated and trained to provide an inversion procedure to single out the
geometric parameters of the fault. Five among these latter, Length, Width, Dip, Strike, Depth,
have been simultaneously inverted. The result is in agreement with those results based on
different approaches. Furthermore the method seems very promising and leads to improve the
studies concerning the combined use of neural networks and InSAR technique
earthquake damage mapping by using remotely sensed data the haiti case study
This work proposes methodologies aimed at evaluating the sensitivity of optical and synthetic aperture radar (SAR) change features obtained from satellite images with respect to the damage grade due to an earthquake. The test case is the Mw 7.0 earthquake that hit Haiti on January 12, 2010, located 25 km west–south–west of the city of Port-au-Prince. The disastrous shock caused the collapse of a huge number of buildings and widespread damage. The objective is to investigate possible parameters that can affect the robustness and sensitivity of the proposed methods derived from the literature. It is worth noting how the proposed analysis concerns the estimation of derived features at object scale. For this purpose, a segmentation of the study area into several regions has been done by considering a set of polygons, over the city of Port-au-Prince, extracted from the open source open street map geo-database. The analysis of change detection indicators is based on ground truth information collected during a postearthquake survey and is available from a Joint Research Centre database. The resulting damage map is expressed in terms of collapse ratio, thus indicating the areas with a greater number of collapsed buildings. The available satellite dataset is composed of optical and SAR images, collected before and after the seismic event. In particular, we used two GeoEye-1 optical images (one preseismic and one postseismic) and three TerraSAR-X SAR images (two preseismic and one postseismic). Previous studies allowed us to identify some features having a good sensitivity with damage at the object scale. Regarding the optical data, we selected the normalized difference index and two quantities coming from the information theory, namely the Kullback–Libler divergence (KLD) and the mutual information (MI). In addition, for the SAR data, we picked out the intensity correlation difference and the KLD parameter. In order to analyze the capability of these parameters to correctly detect damaged areas, two different classifiers were used: the Naive Bayes and the support vector machine classifiers. The classification results demonstrate that the simultaneous use of several change features from Earth observations can improve the damage estimation at object scale
Assessing the volcanic hazard for Rome. 40Ar/39Ar and In-SAR constraints on the most recent eruptive activity and present-day uplift at Colli Albani Volcanic District
We present new 40Ar/39Ar data which allow us to refine the recurrence time for the most recent eruptive activity occurred at Colli Albani Volcanic District (CAVD) and constrain its geographic area. Time elapsed since the last eruption (36 kyr) overruns the recurrence time (31 kyr) in the last 100 kyr. New interferometric synthetic aperture radar data, covering the years 1993–2010, reveal ongoing inflation with maximum uplift rates (>2 mm/yr) in the area hosting the most recent (<200 ka) vents, suggesting that the observed uplift might be caused by magma injection within the youngest plumbing system. Finally, we frame the present deformation within the structural pattern of the area of Rome, characterized by 50 m of regional uplift since 200 ka and by geologic evidence for a recent (<2000 years) switch of the local stress-field, highlighting that the precursors of a new phase of volcanic activity are likely occurring at the CAVD
The relationship between seismic deformation and deep seated gravitational
This paper re-evaluates the origin of some peculiar patterns of ground deformation observed by
space geodetic techniques during the two earthquakes of September 26th of the Colfiorito seismic
sequence. The surface displacement field due to the fault dislocation, as modeled with the classic
Okada elastic formulations, shows some areas with high residuals which cannot be attributed to
unsimulated model complexities. The latter was investigated using geomorphological analysis, by
recognising the geologic evidence of deep seated gravitational slope deformations (DSGSD) of the
block-slide type. The shape and direction of the co-seismic ground displacement observed in these
areas are correlated with the expected pattern of movement produced by the reactivation of the
identified DSGSD. At least a few centimetres of negative Line of Sight ground displacement was
determined for the Costa Picchio, Mt. Pennino, and Mt. Prefoglio areas. A considerable horizontal
component of movement in the Costa Picchio DSGSD is evident from a qualitative analysis of
ascending and descending interferograms. The timing of the geodetic data indicates that the ground
movement occurred during the seismic shaking, and that it did not progress appreciably during the
following months. In this work it has been verified the seismic triggering of DSGSD previously
hypothesized by many authors. A further implication is that in the assessment of DSGSD hazard it is
necessary to consider the seismic input as an important cause of acceleration of the deformation rates
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