Ground deformation detection of the greater area of Thessaloniki (Northern Greece) using radar interferometry techniques

In the present study SAR interferometric techniques (stacking of conventional interferograms and Permanent Scatterers), using images from satellites ERS-1 and 2, have been applied to the region of Thessaloniki (northern Greece). The period covered by the images is 1992–2000. Both techniques gave good quantitative and qualitative results. The interferometric products were used to study ground surface deformation phenomena that could be related to the local tectonic context, the exploitation of underground water and sediments compaction. <br><br> The city of Thessaloniki shows relatively stable ground conditions. Subsidence in four locations, mainly in the area surrounding the city of Thessaloniki, has been detected and assessed. Two of the sites (Sindos-Kalochori and Langadhas) were already known from previous studies as subsiding areas, using ground base measurements. On the contrary the other two sites in the northern suburbs of Thessaloniki (Oreokastro) and in the south-east (airport area) were unknown as areas of subsidence. A further investigation based on fieldwork is needed in these two areas. Finally, an attempt to interpret the observed deformation, according to the geological regime of the area and its anthropogenic activities, has been carried out

HYDROTHERMAL ALTERATION ZONES DETECTION IN LIMNOS ISLAND, THROUGH THE APPLICATION OF REMOTE SENSING

Στην παρούσα εργασία αναλύθηκαν τα δεδομένα του θεματικού χαρτογράφου Landsat 8, με σκοπό την διάκριση και αναγνώριση ζωνών υδροθερμικής εξαλλοίωσης στην ευρύτερη περιοχή της νήσου Λήμνου. Η προ-επεξεργασία των δορυφορικών δεδομένων αφορούσε την δημιουργία μάσκας της βλάστησης και της θάλασσας. Για να βελτιωθεί η χωρική διακριτική ικανότητα στα 15 m έγινε συγχώνευση δεδομένων. Ένας χάρτης γραμμώσεων παρήχθη από την πανγχρωματική εικόνα προσδίδοντας τη γενική τεκτονική άποψη του νησιού. Η ανίχνευση και η χαρτογράφηση των εξαλλοιωμένων πετρωμάτων πραγματοποιήθηκε χρησιμοποιώντας λόγους καναλιών και ακολούθως σύνθετων ψευδέγχρωμων εικόνων. Η ψευδέγχρωμη εικόνa 10, 11, 7 (RGB) δείχνει την φασματική υπογραφή και την κατανομή των πυριτικών ορυκτών. Οι λόγοι καναλιών 6/7, 4/2, 6/5, αποκαλύπτουν ζώνες εξαλλοίωσης που περιέχουν οξείδια του σιδήρου, αργιλική εξαλλοίωση, και σιδρούχα (Fe 2+) ορυκτά. Η ανάλυση έδειξε ότι οι υδροθερμικά εξαλλοιωμένες περιοχές στη νήσο Λήμνο τοποθετούνται στα δυτικά της Λήμνου, στη χερσόνησο του Φακού, στις Σάρδες, στο Ρουσσοπούλι και περιμετρικά στο 1596 λόφο Παραδείσι. Αυτές οι περιοχές συγκρίθηκαν και τεκμηριώθηκαν με εργασίες πεδίου που πραγματοποιήθηκαν από προηγούμενους ερευνητές. Συνοψίζοντας, οι υδροθερμικές ζώνες εξαλλοίωσης μπορούν να εντοπιστούν και να χαρτογραφηθούν χρησιμοποιώντας μέτριας ανάλυσης δορυφορικά πολυφασματικά δεδομένα. Ωστόσο, για την αναγνώριση και χαρτογράφηση συγκεκριμένων τύπων ορυκτών και πετρωμάτων, απαιτείται ένας αισθητήρας υψηλής φασματικής ανάλυσηςIn this study we use Landsat 8 OLI satellite imagery in order to identify and map alteration zones in Limnos island (N. Aegean, Greece). Pre-processing included sea and vegetation masking. In order to enhance spatial resolution, data fusion to 15m is performed. A lineament map is extracted from the panchromatic image that gives the general tectonic view of the island. The detection and mapping of alteration minerals is performed using specific band ratios and consequent composite images. The colour composite using bands 10, 11, 7 (RGB) show the spectral signature and general distribution of silica. Band ratios 6/7, 4/2, 6/5, reveal alteration zones containing iron oxides, clay alteration and ferrous minerals correspondingly. The aforementioned analysis has shown that hydrothermally alteration areas in Limnos are located in the west part of the island and at the Fakos Peninsula, Sardes, Roussopouli and Paradeisi hill. These areas are compared and validated with the reported field work. We conclude that hydrothermal alteration zones can indeed be detected and mapped using medium resolution satellite multispectral data. However, for the identification and mapping of specific types of rocks and minerals, a sensor with high spectral resolution is required.

Deformation in Nisyros volcano (Greece) using differential radar interferometry

Nisyros Volcano located at the southeastern Aegean Sea (Greece) has recently shown (1996-97) a high seismic activity, associated with a significant deformation has determined by DGPS measurements. The determination of the overall deformation of the island was also attempted by Differential Radar Interferometry (DInSAR). The DInSAR analysis has been applied using the ERS-2 satellite data, covering the period 1996-1999. The removal of the interferometric phase related to the topography has been done using an external high resolution DEM. Two areas of the island show a good coherence, the southwestern and the eastern part. Almost two interferometric fringes were respectively recognized and evaluated. These two zones coincide with the main tectonic fractures of the island. The time separation and resolution, which consist important factors, for the extraction of the effective information and the quality of the finally produced differential interferogram, seem however that influence very slight its accuracy. The deformation outlined by the interferogram is compatible with the existing differential GPS observations

LANDSLIDE SUSCEPTIBILITY MAPPING BY GIS-BASED QUALITATIVE WEIGHTING PROCEDURE IN CORINTH AREA

Landslide susceptibility mapping refers to a division of the land into zones of varying degree of stability based on an estimated significance of causative factors in inducing the instability. Maps of landslide susceptibility (relative hazard) are usually prepared on regional scales from 1:25.000 - 1:50.000. An advantage of regional studies is that they allow rapid assessment and hence larger areas can be covered in short durations. Factors (data layers) used for the preparation of the landslide susceptibility map were obtained from different sources such as topographic maps, geological maps and satellite images. All the above data layers were converted to raster format in the GIS, each representing an independent variable of a constructed spatial database. Computerization of the database would be necessary to make such analysis possible within an acceptable time frame. According to their relative importance to slope instability in the study area, the various classes of different data layers were assigned weights between 0,0 and 1,0 (collectively adding to 1,0). The overall susceptibility was calculated as an index named SPI (Susceptibility Potential Index), expressing the combination of the different weighted layers into a single map using a certain combination rule. Reclassification of susceptibility scores, based on natural breaks in the cumulative frequency histogram of SPI values, were used to delineate various susceptibility zones namely, very high, high, moderate, low and very low. Verification of results by overlaying susceptibility map and landslide inventory data and adjustment of zone's boundaries was the last stage of the study, allowing the reconsideration in some cases of the weights give

SENTINEL-1 DATA TO MAP FLOODED AREAS: THE ROLE OF INSAR COHERENCE AND POLARIMETRIC INFORMATION

Τα SAR δεδομένα παρατήρησης της Γης μπορούν να προσφέρουν χάρτες πλημμυρικής έκτασης και πληροφοριών υψηλής ποιότητας για την καλύτερη εκτίμηση του κινδύνου πλημμύρας κατά συνέπεια το σχεδιασμό, καθώς και για την υποστήριξη των πολιτικών αρχών υπέρ της προστασίας κατά τη φάση έκτακτης ανάγκης. Το πεδίο εφαρμογής του παρόντος εγγράφου είναι να δημιουργήσει χάρτες πλημμυρικής έκτασης από μια σειρά εικόνων SAR της λεκάνης του Έβρου, που αντιπροσωπεύει μια διασυνοριακή κοίτη πλημμυρών. Η μελέτη χρησιμοποιεί χρονολογικές σειρές εικόνων SAR του Copernicus δορυφορικού συστήματος Sentinel-1 που καλύπτει την περίοδο Οκτώβριος 2014-Μάιος 2015. Η μεθοδολογία προσπαθεί να προσδιορίσει την πλημμύρα που συμβαίνει σε τρεις κύριες κατηγορίες κάλυψης γης, όπως είναι οι αστικές περιοχές, γυμνά ή κακώς βλάστηση εδάφους και περιοχές με βλάστηση, εκμεταλλευόμενοι τα εναλλασσόμενη πόλωση SAR κανάλια backscattering, και τη συνάφεια συμβολομετρίας για τον καλύτερο χαρακτηρισμό του τοπίου. Χρησιμοποιώντας εναλλασσόμενη πόλωση SAR δεδομένα παρέχει την ευκαιρία να υπάρχει μια καλύτερη κατανόηση και ερμηνεία της ανίχνευσης πλημμύρας λόγω του διαφορετικού τρόπου που αντιδρά η κάλυψη γης σε διαφορετικές 1731 πολώσεις. Έτσι, με την εφαρμογή της εκτίμησης της συμβολομετρικής συνάφειας μπορούμε να επιτύχουμε ένα καλύτερη καταγραφή και γνώση των πλημμυρισμένων περιοχών, στη πάροδο του χρόνου, στη συγκεκριμένη περιοχή.SAR earth observation data can provide high quality flood maps and information to better assess the flood risk accordingly planning as well as to support civil protection authorities during emergency phase. The scope of this paper is to create flood extent maps from a series of SAR scenes of the Evros basin which represents a transboundary floodplain. The study uses time series SAR images of Sentnel-1 ESA’s Copernicus satellite system covering the period October 2014 to May 2015. The methodology tries to identify the flood that occurs in three main land cover classes, such as urban areas, bare or poorly vegetated soil and vegetated areas, taking advantage of co- and cross-polarized SAR backscattering channels, and the InSAR coherence to better characterize the landscape. Dual-pol SAR data provides the opportunity to have a better understanding and interpretation of flood detection due to way different land cover react to different polarizations. Thus, with the implementation of InSAR coherence estimation we may achieve a better record and knowledge of the flooded areas, over time, in the specific region.

SLOPE INSTABILITY MONITORING BY SPACE-BORNE SAR INTERFEROMETRY: PRELIMINARY RESULTS FROM PANACHAICO MOUNTAIN (WESTERN GREECE)

Space borne differential synthetic aperture radar interferometry (DInSAR) has already proven its potential for mapping ground deformation phenomena, e.g. earthquakes, volcano dynamics, etc covering in continuity large areas. The innovative Persistent Scatterers Interferometry (PSI) technique, which overcomes several limitations of conventional SAR differential interferometry especially for applications in landslide studies, is suitable for monitoring slope deformations with millimetric precision. With PSI technique we detect the deformation, for long periods, that occur in an area as average annual deformation (mm/y) and is not spatially continuous but in terms of points (point targets). The aim of this study is to present preliminary results on the monitoring of slope instability in Panachaiko Mountain and particularly of the slopes facing the city of Patras. For this purpose we processed and analysed 42 ERS 1 and ERS 2 SAR scenes acquired in the time span 1992 and 2001, by applying the Interferometric Point Target Analysis algorithm. Point target reflectors with stable radar response over time were selected. In this case most of the point targets correspond to buildings of the local settlements or to rock outcrops. Additionally, millimetric target displacements along the line of sight direction were detected allowing measurements of slow terrain motion

DIFFERENTIAL INTERFEROMETRY AS A TOOL OF AN EARLY WARNING SYSTEM IN REDUCING THE VOLCANO RISK: THE CASE OF NISYROS VOLCANO

In this study an attempt to evaluate the possibility to use the interferometric (InSAR) technique as an operational tool in an early warning system concerning the volcanic hazard, is presented. The InSAR techniques was appied in Nisyros volcanic island which during 1996-1998 show an intensive seismic unrest. Two interferometric images were created covering the period before the seismic activity (1995-1996). In the two interferometric images fringe patterns of deformation were recognized related to the ground deformation occured before the seismic unrest period. The operational capabilities of the technique is mainly restricted by the low repetitevily of the image aquisitions and the parameters to take in consideration like perpendicular baseline, atmospheric conditions et