KARSTIC LANDSCAPE STUDY BASED ON REMOTE SENSING DATA: THE CASE OF KSIROMERO REGION, AITOLOAKARNANIA - WESTERN GREECE

The aim of this study is to investigate and recognize karst landforms in the area of Ksiromero (Aitoloakarnania, Western Greece) based on medium resolution remote sensing data. In order to highlight karstic structures appropriate and innovative methodologies of image analysis have been developed, applied and compared. In particular, the original Landsat 5 TM bands have been, first, ad-hoc stretched and then processed to obtain the so-called Tasseled Cap Features and the Principal Component images. Finally, a comparative study between the two methods has been carried out

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.

Ground deformation measurements over Lake Trichonis based on SAR interferometry.

Ο σκοπός της παρούσας μελέτης είναι o εντοπισμός της παραμόρφωση του εδάφους στην ευρύτερη περιοχή της Λίμνης Τριχωνίδας (Δυτική Ελλάδα), εστιάζοντας κυρίως στο σεισμικό φαινόμενο του Απριλίου 2007 με την σμήνοσειρά σεισμών που σημειώθηκε στην περιοχή της λίμνης. Η περιοχή συνιστά μία pull-apart λεκάνη, η οποία παρουσιάζει γενικότερα μία έντονη σεισμική δραστηριότητα λόγο των δύο ενεργών ρηγμάτων κατά μήκος του βόρειου και νότιου περιθωρίου της. Η σμηνοσειρά ξεκίνησε με μικρού μεγέθους σεισμούς, στις 9 Απριλίου 2007 ενώ ακλούθησαν τρία ισχυρότερα σεισμικά γεγονότα στις 10 Απριλίου 2007, με μεγέθη που κυμαίνονται από 5,0 έως 5,2 Mw, τα οποία και αποτέλεσαν τα μεγαλύτερα ολόκληρης της ακολουθίας. Η σεισμική δραστηριότητα συνεχίστηκε για περισσότερο από ένα μήνα με μικρότερα σεισμικά γεγονότα. Βάσει των σεισμολογικών δεδομένων οριοθετήθηκαν δύο νέα κανονικά ρήγματα ΒΔ-ΝΑ διεύθυνσης κατά μήκος της νοτιοανατολικής όχθης της λίμνης. Χρησιμοποιώντας ένα σύνολο 28 εικόνων Ραντάρ, του δορυφόρου ENVISAT για την περίοδο από το Φεβρουάριο του 2003 μέχρι τον Φεβρουάριο του 2010 εφαρμόστηκε η τεχνική της διαφορικής συμβολομετρίας και πιο συγκεκριμένα διαφορετικές τεχνικές σώρευσης συμβολογραφημάτων με σκοπό την ανίχνευση και χαρτογράφηση των παραμορφώσεων του εδάφους που προκλήθηκε από την «σμηνοσειρά σεισμών». Σύμφωνα με τα αποτελέσματά των συγκεκριμένων τεχνικών αποδεικνύεται ότι η περιοχή παρουσιάζει εντελώς διαφορετικό καθεστώς εδαφικής παραμόρφωση κατά τη διάρκεια της προ-σεισμικής και μετα-σεισμικής περιόδου σε σχέση με την συν-σεισμική.The aim of this study is to detect and measure ground deformation over the broader area of Lake Trichonis (Western Greece), focusing mainly on the April 2007 earthquake swarm which occurred at the vicinity of the Lake. The area, forming a pull-apart basin, presented historically an intense seismic activity along the two active normal faults at the northern and southern part of the Lake. The swarminitiated by small magnitude events on the 8th of April 2007 followed by the three strongest events of the entire sequence on the 10th of April 2007, with magnitudes ranging from 5.0 to 5.2 Mw. The seismic activity continued for longer with smaller seismic events. Based on seismological data this activity was attributed to two unmapped NW SE trending normal faults that bounds the SE bank of the Lake. Using a dataset of 28 ENVISAT ASAR scenes covering the period from February 2003 until February 2010 (~7 yr), different Interferometric Stacking techniques was applied in order to quantify the ground deformation induced by the earthquake swarm as well as its effect on the inter-seismic deformation pattern of the area. Our results indicate that co-seismic motion differs significantly from that observedduring the pre- and post- swarm periods. The co-seismic pattern reveals subsidence at the northern and uplift at the southern lake sides, consistent with the structural model already proposed for the area. For the pre- and post-seismic periods both sides of the Lake show stability or low rates of subsidence with higher deformationvelocity rates for the period after the seismic activity, possibly attributed to postseismic relaxation. Our findings imply that inter-seismic ground deformation does not necessary follow the deformation pattern observed during seismic triggering, thus, long-term geodetic observations such as those provided by SAR interferometry are valuable in order to fully characterize the geodynamic behavior of an active region

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

Geomorphological observations and related natural hazards using merged remotely sensed data: A case study in the corinthos area (NE Peloponnese, S. Greece)

Natural hazards are mostly related to the activation of combined geomorphological and geological processes that control landform development. The study area is located in the NE part of Peloponnese (Corinthos prefecture). It is a typical agricultural area with intense relief, the result of active tectonics and important human intervention. This study demonstrates the benefits from the synergism of SAR data (ERS-2) and optical data (SPOT2-XS) in order to highlight the possible natural-hazard-prone areas. These data give different and complementary information since the radar signal depends mostly on topography, surface roughness and soil moisture, whereas the visible/infrared channels provide spectral information mostly on vegetation and land use/cover. The application presented here was focused on the enhancement of the high erosion risk areas, the improvement of the terrain interpretation, the mapping and highlighting of the landform morphology, and a more accurate determination of the main factors that control the flooding risk of Corinthos town

Use of Sentinel-1 imagery for flood management in a reservoir-regulated river basin

International audienc

Persistent Scatterers InSAR to detect ground deformation over Rio-Antirio area (Western Greece) for the period 1992-2000

The aim of this paper is to detect ground deformation detection in the Rio-Antirio area (Western Greece), between 1992 and 2000. The construction of Rio-Antirio bridge, commenced in year 2000 and completed in 2004 when its operation was launched, demands the study of the historic deformation of the broader area. The Interferometric Point Target Analysis (IPTA) was applied using a dataset of 42 ERS-1 and 2 scenes. Two separate IPTA processing were performed using different reference points for Rio and Antirio respectively. It would not be possible to unwrap the entire scenes using a single reference point because of the presence of the sea water mass between Rio and Antirio. The majority of the point targets show subsidence for the area of Rio ranging between - 1.8 mm/year and - 6.2 mm/year and for the Antirio area stability or subsidence rates of less than 2 mm/year. Additionally, the deformation history for a number of point targets for both areas was investigated. The detected subsidence of the coastal plains and specially this of Rio could be attributed to the presence of active faults as the area is located over the hanging wall of the fault zone. © 2008 Elsevier B.V. All rights reserved