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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.

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.

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.

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.

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.

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