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Kaskara M.,Institute of Space Applications and Remote Sensing | Barberopoulou A.,Institute of Space Applications and Remote Sensing | Papoutsis I.,Institute of Space Applications and Remote Sensing | Kontoes H.,Institute of Space Applications and Remote Sensing | And 2 more authors.
European Space Agency, (Special Publication) ESA SP | Year: 2015

Crete lies in the forearc basin of the collision zone between the Eurasian and African plates - one of the highest seismicity regions in the world. The purpose of this study is to map ground deformation using time series analysis. Up until now, most geodetic observations used only GPS data. The key difference between space-based measurements and GPS or in-situ analysis is the good spatial coverage and the sensitivity of InSAR in the vertical direction. Using Persistent Scatterers (PS) and Small Baseline Subset techniques, deformation maps of the entire island of Crete are produced for the first time and geophysical interpretation is provided. A significant uplift of +9 mm/yr is observed at the centre of the island due to the subduction zone processes. Subsidence up to -9 mm/yr is also detected at Messara valley on the Southern part of central Crete, due to anthropogenic activities. A modelling approach was adopted to explain the deformation due to the subduction zone.


Kaskara M.,Institute of Space Applications and Remote Sensing | Atzori S.,Italian National Institute of Geophysics and Volcanology | Papoutsis I.,Institute of Space Applications and Remote Sensing | Kontoes C.,Institute of Space Applications and Remote Sensing | And 2 more authors.
European Space Agency, (Special Publication) ESA SP | Year: 2016

Santorini Volcanic Complex (SVC) is the most active part of the South Aegean (Hellenic) Volcanic Arc, which marks the subduction of the African underneath the Eurasian plate, and is considered a prime site for conducting geophysical research. The SVC showed signs of unrest in January 2011 and has been inflating almost radially around a source northern of the Kameni islands. We present deformation maps for the SVC as obtained from the multi-temporal analysis of Synthetic Aperture Radar (SAR) imagery for the post-inflation period, using datasets from COSMO-SkyMed (CSK) and TerraSAR-X (TSX) satellites. Displacement rates indicate mainly subsidence at Nea Kameni Island and horizontal motion at the northern part of the caldera. These movements may be due to smooth deflation of the volcano. The signal for the rest of the SVC indicates a phase of relative stability. Finally, we model our results assuming a Mogi model for magma chambers. The data inversion was based on InSAR data and also accounting GPS measurements.


Psychogyiou C.,Institute of Space Applications and Remote Sensing | Papoutsis I.,Institute of Space Applications and Remote Sensing | Kontoes C.,Institute of Space Applications and Remote Sensing | Poyiadji E.,Institute of Geology and Mineral Exploration | And 2 more authors.
European Space Agency, (Special Publication) ESA SP | Year: 2015

The high frequency of landslide occurrences in Central and Western Greece, part of the Pindus mountain range, is now approached by exploiting the high temporal sampling rate of historical ERS-1/2 and ENVISAT SAR imagery in combination with the Multi Temporal Interferometry (MTI) technique. An existing wellestablished ground truth dataset is updated and enriched with the diachronic MTI results. Critical areas prone to slide are evaluated through susceptibility assessment and mapping taking into consideration the challenging environmental factors which dominate at the area of interest. A set of supplementary interesting geophysical and structural MTI detections at the region of analysis are additionally discussed.


Nikos S.,Aristotle University of Thessaloniki | Nikos S.,Institute of Space Applications and Remote Sensing | Ioannis P.,Institute of Space Applications and Remote Sensing | Constantinos L.,National Technical University of Athens | And 3 more authors.
Engineering Geology | Year: 2016

Land subsidence in the broader Kalochori village region, at the west side of Thessaloniki, has been recorded since the early 1960s reaching gradually, next to the coastline, maximum values of 3-4 m. Temporal monitoring of terrain movements are exploited and combined with in-situ data to enhance understanding of the deformation signals. Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) multi-temporal Interferometric approach are applied for the analysis of a 20 year ERS 1, 2 and ENVISAT dataset. The velocities estimated for the ERS dataset are in excellent accordance with previous studies, depicting subsidence with magnitude up to 35 mm/year. The intriguing output of the ENVISAT data archive (2003-2010) shows that, during the second decade, there was a change in motion trend, from subsidence to uplift. The fact that this uplifting trend of the second decade is well correlated with hydrogeological data of the area that show a synchronous rise of the aquifer level, verifies the dominating driver of the human factor concerning the land subsidence phenomena taking place the last 55 years. This conclusion is further supported by the fact that since 2007 the uplifting signal becomes smoother, following the smoother recovery of the aquifers. © 2016 Elsevier B.V.


Svigkas N.,Aristotle University of Thessaloniki | Svigkas N.,Institute of Space Applications and Remote Sensing | Papoutsis I.,Institute of Space Applications and Remote Sensing | Loupasakis C.,National Technical University of Athens | And 2 more authors.
European Space Agency, (Special Publication) ESA SP | Year: 2015

Temporal monitoring of terrain movements and satellite observations are used here to monitor geophysical Natural Hazards in northern Greece for the period 1992-2010, applying Persistent Scatterer Interferometry and Small Baseline Subset techniques, in an attempt to address their causes: anthropogenic or natural due to geological and geomorphological evolution. Our study highlights new areas that were previously unknown to be at risk and validates the remote sensing estimates using drill data, geomechanics and hydrogeology results. Site-specific results are presented for the broader urban area of Thessaloniki, Thessaloniki plain (Nea Malgara-Kimina, Chalastra) and the broader area of Katerini.


Van Oers P.,University of Amsterdam | Van Oers P.,University of Southampton | Markoff S.,University of Amsterdam | Rahoui F.,University Paris Diderot | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

GRS 1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however - referred to as the plateau state - may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. However, while generally black hole binaries quench their jets when the luminosity becomes too high, GRS 1915+105 seems to sustain them despite the fact that it accretes at near- or super-Eddington rates. In order to investigate the relationship between the plateau and the hard state, we fit two multiwavelength observations using a steady-state outflow-dominated model, developed for hard-state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fitting model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates. © 2010 The Authors. Journal compilation © 2010 RAS.


Petropoulos G.P.,Institute of Space Applications and Remote Sensing | Kontoes C.,Institute of Space Applications and Remote Sensing | Keramitsoglou I.,Institute of Space Applications and Remote Sensing
International Journal of Applied Earth Observation and Geoinformation | Year: 2011

Information on burnt area is of critical importance in many applications as for example in assessing the disturbance of natural ecosystems due to a fire or in proving important information to policy makers on the land cover changes for establishing restoration policies of fire-affected regions. Such information is commonly obtained through remote sensing image thematic classification and a wide range of classifiers have been suggested for this purpose. The objectiveof the present study has been to investigate the use of Support Vector Machines (SVMs) classifier combined with multispectral Landsat TM image for obtaining burnt area mapping. As a case study a typical Mediterranean landscape in Greece was used, in which occurred one of the most devastating fires during the summer of 2007. Accuracy assessment was based on the classification overall statistical accuracy results and also on comparisons of the derived burnt area estimates versus validated estimates from the Risk-EOS Burnt Scar Mapping service. Results from the implementation of the SVM using diverse kernel functions showed an average overall classification accuracy of 95.87% and a mean kappa coefficient of 0.948, with the burnt area class always clearly separable from all the other classes used in the classification scheme. Total burnt area estimate computed from the SVM was also in close agreement with that from Risk-EOS (mean difference of less than 1%). Analysis also indicated that, at least for the studied here fire, the inclusion of the two middle infrared spectral bands TM5 and TM7 of TM sensor as well as the selection of the kernel function in SVM implementation have a negligible effect in both the overall classification performance and in the delineation of total burnt area. Overall, results exemplified the appropriateness of the spatial and spectral resolution of the Landsat TM imagery combined with the SVM in obtaining rapid and cost-effective post-fire analysis. This is of considerable scientific and practical value, given the present open access to the archived and new observations from this satellite radiometer globally. © 2010 Elsevier B.V.


PubMed | Institute of Space Applications and Remote Sensing
Type: Journal Article | Journal: Sensors (Basel, Switzerland) | Year: 2012

The Permanent Scatterers Interferometric SAR technique (PSInSAR) is a method that accurately estimates the near vertical terrain deformation rates, of the order of 1 mm year(-1), overcoming the physical and technical restrictions of classic InSAR. In this paper the method is strengthened by creating a robust processing chain, incorporating PSInSAR analysis together with algorithmic adaptations for Permanent Scatterer Candidates (PSCs) and Permanent Scatterers (PSs) selection. The processing chain, called PerSePHONE, was applied and validated in the geophysically active area of the Gulf of Corinth. The analysis indicated a clear subsidence trend in the north-eastern part of the gulf, with the maximum deformation of 2.5 mm year(-1) occurring in the region north of the Gulf of Alkyonides. The validity of the results was assessed against geophysical/geological and geodetic studies conducted in the area, which include continuous seismic profiling data and GPS height measurements. All these observations converge to the same deformation pattern as the one derived by the PSInSAR technique.


PubMed | National Technical University of Athens and Institute of Space Applications and Remote Sensing
Type: Journal Article | Journal: Sensors (Basel, Switzerland) | Year: 2016

The primary objective of this paper is the evaluation of the InSAR derived displacement field caused by the 07/09/1999 Athens earthquake, using as reference an external data source provided by terrestrial surveying along the Mornos river open aqueduct. To accomplish this, a processing chain to render comparable the leveling measurements and the interferometric derived measurements has been developed. The distinct steps proposed include a solution for reducing the orbital and atmospheric interferometric fringes and an innovative method to compute the actual InSAR estimated vertical ground subsidence, for direct comparison with the leveling data. Results indicate that the modeled deformation derived from a series of stacked interferograms, falls entirely within the confidence interval assessed for the terrestrial surveying data.

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