Issaak Parcharidis

Long-and Short-Term Deformation Monitoring of Santorini Volcano: Unrest Evidence by DInSAR Analysis

Santorini Volcano is an active strato volcano, located at the central part of the Hellenic Volcanic Arc, developing ad retro of the Hellenic Arc and Trench. The explosive history of the volcano dates back to 1645 BC with the Minoan eruption, while it is documented to have produced at least ten eruptions until 1950 AD. The most recent volcanic unrest began in early 2011. Multi-reference Synthetic Aperture Radar (SAR) Interferometric techniques were applied to study the evolution of ground deformation during 1992-2011, with the use of ERS-1 and -2 and ENVISAT radar imagery. Datasets of common acquisition geometry were added into a single stack so as to obtain the linear deformation rates by means of phase averaging. However, to reveal the deformation history of the volcano, Singular Value Decomposition (SVD) method was implemented. This allowed retrieving ground deformation time-series on a pixel basis over regions with high temporal coherence levels. Results from independent tracks, agreeing with each other, suggest a deformation rate of approximately 5 mm/yr of subsidence at the southern part of Nea Kammeni Volcano, for the period 1992-2010. For the unrest period of 2011, intense uplift of 4.8 cm was observed throughout Nea Kammeni. Global Positioning System (GPS) observations from a local geodetic network confirm the DInSAR findings.

Time Series Synthetic Aperture Radar Interferometry for Ground Deformation Monitoring over a Small Scale Tectonically Active Deltaic Environment (Mornos, Central Greece)

ABSTRACT Parcharidis, I.; Kourkouli, P.; Karymbalis, E.; Foumelis, M., and Karathanassi, V., 2013, Time series synthetic aperture radar interferometry for ground deformation monitoring over a small scale tectonically active deltaic environment (Mornos, Central Greece). This study deals with the estimation of subtle ground deformation at millimetric accuracy over the broader area of the Mornos River delta in Central Greece and its spatio-temporal distribution for the period between 1992 and 2009 through Persistent Scatterers Interferometry (PSI). The results showed that the majority of the scatterers, which show subsidence, are located within the delta plain with mean subsidence rates throughout the delta varying between −7.2 and +0.7 mm/y. An attempt is made to highlight the geographic distribution, the amplitude, and the causes of the observed delta plain subsidence. The positive correlation between the thickness of the fine-grained Holocene deltaic deposits and the subsidence rates reveals that the main cause is the natural compaction of sediments. The highest subsidence is observed at Bouka Karahassani village, which corresponds to the area of the most recently abandoned river mouth, which is intensely eroded by marine processes. Apart from the dominance of fine sediments in the study area, subsidence may also be attributed to submarine gravitational mass movements along the steep slopes of the prodelta as well as to the reduction of sediment load after the dam construction in 1979. The NW part of the delta seems to have been affected by aseismic slip along a NE-SW trending normal fault buried beneath the alluvial deposits of the Skala torrent fan.

Surface Motion and Structural Instability Monitoring of Ming Dynasty City Walls by Two-Step Tomo-PSInSAR Approach in Nanjing City, China

Spaceborne Multi-Temporal Synthetic Aperture Radar (SAR) Interferometry (MT-InSAR) has been a valuable tool in mapping motion phenomena in different scenarios. Recently, the capabilities of MT-InSAR for risk monitoring and preventive analysis of heritage sites have increasingly been exploited. Considering the limitations of conventional MT-InSAR techniques, in this study a two-step Tomography-based Persistent Scatterers (PS) Interferometry (Tomo-PSInSAR) approach is proposed for monitoring ground deformation and structural instabilities over the Ancient City Walls (Ming Dynasty) in Nanjing city, China. For the purpose of this study we utilized 26 Stripmap acquisitions from TerraSAR-X and TanDEM-X missions, spanning from May 2013 to February 2015. As a first step, regional-scale surface deformation rates on single PSs were derived (ranging from −40 to +5 mm/year) and used for identifying deformation hotspots as well as for the investigation of a potential correlation between urbanization and the occurrence of surface subsidence. As a second step, structural instability parameters of ancient walls (linear motion rates, non-linear motions and material thermodynamics) were estimated by an extended four-dimensional Tomo-PSInSAR model. The model applies a two-tier network strategy; that is, the detection of most reliable single PSs in the first-tier Delaunay triangulation network followed by the detection of remaining single PSs and double PSs on the second-tier local star network referring to single SPs extracted in the first-tier network. Consequently, a preliminary phase calibration relevant to the Atmospheric Phase Screen (APS) is not needed. Motion heterogeneities in the spatial domain, either caused by thermal kinetics or displacement trends, were also considered. This study underlines the potential of the proposed Tomo-PSInSAR solution for the monitoring and conservation of cultural heritage sites. The proposed approach offers a quantitative indicator to local authorities and planners for assessing potential damages as well as for the design of remediation activities.

Crustal stress and seismic activity in the Ionian archipelago as inferred by satellite- and ground-based observations, Kefallinia, Greece

Abstract Different observational techniques are compared in order to investigate possible correlations in seismic activity. The study site is the island of Kefallinà (Greece), where measurements available included (1) DInSAR, DGPS, and DEM data, (2) soil exhalation measured by monitoring Radon (Rn) well content, and (3) acoustic emissions (AE) at high and low frequency (point-like records with high temporal resolution). AE records provide: (1) relative time variation of the applied stress intensity and (2) the state of fatigue of stressed rock volumes, the AE source. Our results indicate that the large spatial scale (poor time resolution) may be considered quite satisfactory, whereas fractal analysis of the AE time series displayed some discrepancies when compared to analogous investigations in the Italian Peninsula. Therefore, some refinement is needed in order to reach more precise interpretations of the relevant information available with this kind of data. However, both sets of observations appear in agreement with each other, although more exhaustive investigations would require a suitable array of point-like AE and Rn (or other) measuring sites, as well as longer data series. The latter are particularly helpful for detailed interpretations of the different occurrences within tectonically complex settings where crustal stress crises are marked by various types of geological phenomena.

Deformation monitoring in Kos Island Hellenic volcanic arc, Eastern Greece) using differential interferometry

In this study SAR interferometry technique has been applied over Kos Island (Hellenic Volcanic Arc) in order to detected pre-, coand post-seismic deformation and to compare with the deformation detected in Nisyros Island for the same period using the same interferometric pairs. The seismic unrest activity observed in Nisyros volcano (1996-1999) could produce crustal deformation in the adjacent island of Kos. The results of the interferometric processing show that coand post-seismic deformation was not possible to be detected due to the obtained low coherence. Contrary the results of the interferometric pair of the pre-seismic unrest period show two fringes of deformation in the southwest part of the island, the same amount of deformation was observed in Nisyros island.

Investigation on Bam (Iran) earthquake 26/12/03 based on interferometric coherence

The Bam earthquake of 26/12/2003 (Mw=6.5) demolished the city of Bam and provoked serious damages in Baravat city, which are located in a tectonic intersection zone in the SE of Iran. The present study focus on Bam earthquake seismotectonic investigations and damages assessment based on Envisat interferometric coherence images. Field observations, SAR magnitude and multitemporal SAR images were also used to support and verify the coherence image interpretation. Concerning the damages assessment the results were very poor in terms of recognition and operational capabilities. On the contrary the used of interferometric coherence image came to be very useful for seismic fault and rupture zones detection. Through this method a hidden fault, a parallel segment of the already known Bam fault, was identified.

Remotely sensing data and thematic mapping for sustainable developing in Sperchios river basin (Central Greece)

Policy and decision making in the context of sustainable development requires rapid, effective and efficient access to and integration of appropriate current information from a wide range of sources, including land cover changes information derived from remotely sensed data. Geomorphic factors, such as altitude, slope, aspect and lithology presented in the area comprise the main parameters, including the climate, influencing the distribution of land cover. The use of a Geographic Information System (GIS) allows further spatial analysis of the data derived from remotely sensed images and digital terrain spatial models, and analysis of the impact of land cover change on regional sustainable development. The remotely sensing data used in this study was Landsat 5 TM and Landsat 7 ETM+ images. Normalized Difference Vegetation Index (NDVI) and Selective Principal Component Analysis (SPCA) techniques were applied to detect land cover change and especially vegetation changes from multitemporal satellite data. The area under study is the basin of River Sperchios, which covers an area of some 1.780 km2, is approximately 60-80 km long, 20-30 km wide with its southern and western flanks characterized by high elevations and steep slopes, whilst its northern flank presents lower elevations and more gently slopes. The conclusions obtained show that extensive land cover changes has occurred in the last decades as a result of both natural forces and human activities, which has in turn impacted on the regional sustainable development. The results thus provide very useful information to local government for decision making and policy planning.

Retrieval of nearshore bathymetry in the Gulf of Chania, NW Crete, Greece, from WorldWiew-2 multispectral imagery

Shallow water bathymetry is recognized as one of the most fundamental topics in environmental studies, seabed morphology research and management of the coastal zone. The detailed mapping as well as the long-term monitoring of the changes in shallow marine relief is important for the successful completion of coastal construction and environmental projects. In recent years, optical satellite imagery is proving to be a useful tool to determine coastal bathymetry, as it provides a time- and cost- effective solution to water depths estimation. In this paper, the two most popular and successful approaches for bathymetry retrieval, the Lyzenga (1985) linear bathymetry model and the Stumpf et al. (2003) ratio method, have been applied to Worldview-2 satellite imagery, in order to derive the more accurate bathymetric model for the shallow-water region of the Chania Gulf, located in NW Crete Island, Greece. This area is sea-grass free and is dominated by sandy substrate with a few rocky outcrops. The models are implemented over the total study area - no separation in subareas according to the bottom type. The results are compared with echo sounding ground truth depth data. The outcomes of the statistical analysis indicate that the linear model provides increased accuracy than the ratio one over the sandy bottom. On the contrary, in those parts covered by rocky bottoms, none of the two models provided satisfactory results.

Correlation between land cover and ground vulnerability in Alexandria City (Egypt) using time series SAR interferometry and optical Earth observation data

The main scope of this study is to investigate the potential correlation between land cover and ground vulnerability over Alexandria city, Egypt. Two different datasets for generating ground deformation and land cover maps were used. Hence, two different approaches were followed, a PSI approach for surface displacement mapping and a supervised classification algorithm for land cover/use mapping. The interferometric results show a gradual qualitative and quantitative differentiation of ground deformation from East to West of Alexandria government. We selected three regions of interest, in order to compare the obtained interferometric results with the different land cover types. The ground deformation may be resulted due to different geomorphic and geologic factors encompassing the proximity to the active deltaic plain of the Nile River, the expansion of the urban network within arid regions of recent deposits, the urban density increase, and finally the combination of the above mentioned parameters.

Spatiotemporal hazard mapping of a flood event "migration" in a transboundary river basin as an operational tool in flood risk management

Flood disaster is one of the heaviest disasters in the world. It is necessary to monitor and evaluate the flood disaster in order to mitigate the consequences. As floods do not recognize borders, transboundary flood risk management is imperative in shared river basins. Disaster management is highly dependent on early information and requires data from the whole river basin. Based on the hypothesis that the flood events over the same area with same magnitude have almost identical evolution, it is crucial to develop a repository database of historical flood events. This tool, in the case of extended transboundary river basins, could constitute an operational warning system for the downstream area. The utility of SAR images for flood mapping, was demonstrated by previous studies but the SAR systems in orbit were not characterized by high operational capacity. Copernicus system will fill this gap in operational service for risk management, especially during emergency phase. The operational capabilities have been significantly improved by newly available satellite constellation, such as the Sentinel-1A AB mission, which is able to provide systematic acquisitions with a very high temporal resolution in a wide swath coverage. The present study deals with the monitoring of a transboundary flood event in Evros basin. The objective of the study is to create the “migration story” of the flooded areas on the basis of the evolution in time for the event occurred from October 2014 till May 2015. Flood hazard maps will be created, using SAR-based semi-automatic algorithms and then through the synthesis of the related maps in a GIS-system, a spatiotemporal thematic map of the event will be produced. The thematic map combined with TanDEM-X DEM, 12m/pixel spatial resolution, will define the non- affected areas which is a very useful information for the emergency planning and emergency response phases. The Sentinels meet the main requirements to be an effective and suitable operational tool in transboundary flood risk management.