Demitris Paradissis

National Technical University of Athens | NTUA · Department of Topography

Geodetic measurements based on satellite data has improved the ability of continuous monitoring crustal deformation processes. Continuous Global Navigation Satellite System (GNSS) networks are widely used to estimate tectonic movements. Accuracy, availability and continuity are the main advantages of the GNSS. Higher Geodesy Laboratory of the Natio...

Santorini is located in the central part of the Hellenic Volcanic Arc (South Aegean Sea) and is well known for the Late-Bronze-Age "Minoan" eruption that may have been responsible for the decline of the great Minoan civilization on the island of Crete. To use gravity to probe the internal structure of the volcano and to determine whether there are...

This work derives a mathematical representation of the gravitational potential outside Earth, as well as different functionals of its gravity field, using rectangular harmonics. For the rectangular harmonic analysis in a local Cartesian coordinate system, the necessary transformation from geocentric into local Cartesian coordinates is presented. Th...

Kythira Island is situated at the western Hellenic Arc, which is a region of very high seismicity and tectonic activity. On 8 January 2006, a large seismic event of Mw = 6.7 occurred close to Kythira, in association with the Hellenic subduction zone. We present an extensive multi-temporal interferometry study of ground displacements in Kythira Isla...

Radar Interferometry is a widely used method for estimating ground deformation, as it provides precision to a few millimeters to centimeters, and at the same time, a wide spatial coverage of the study area. On July 9, 1956, one of the strongest earthquakes of the 20th century in the area of the South Aegean, occurred in Amorgos, with a magnitude of...

Precise knowledge of the oceanic Mean Dynamic Topography (MDT) is crucial for a number of geodetic applications , such as vertical datum uniication and marine 5 geoid modelling. The lack of gravity surveys over many regions of the Greek seas and the incapacity of the space borne gradiometry/gravity missions to resolve the small and medium wavelengt...

Santorini is located in the central part of the Hellenic Volcanic Arc (South Aegean Sea) and is well known for the Late-Bronze-Age "Minoan" eruption that might had been responsible for the decline of the great Minoan civilization on Crete island. Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) carried out...

Dionysos Satellite Observatory and Higher Geodesy Laboratory have been in operation since the 60s and their main objective is to fulfill academic and research needs, determined through the ongoing scientific and technological advance in the field of geodesy. They are involved in all scientific domains related to the determination of earth’s size an...

The wider Athens metropolitan area serves as an interesting setting for conducting geodetic studies. On the one hand, it has a complex regional geotectonic characteristic with several active and blind faults, one of which gave the deadly M w 5.9 Athens earthquake on September 1999. On the other hand, the Greek capital is heavily urbanized, and cons...

The wider Athens metropolitan area serves as an interesting setting for conducting geodetic studies. On the one hand, it has a complex regional geotectonic characteristic with several active and blind faults, one of which gave the deadly Mw 5.9 Athens earthquake on September 1999. On the other hand, the Greek capital is heavily urbanized, and const...

Seismological, GPS and historical data suggest that most of the 40 mm yr−1 convergence at the Hellenic Subduction Zone is accommodated through aseismic creep, with earthquakes of MW ≲ 7 rupturing isolated locked patches of the subduction interface. The size and location of these locked patches are poorly constrained despite their importance for ass...

EUREF Analysis Centre Workshop AIU Bern, Switzerland, October 14-15, 2015

On January 26, 2014 a strong earthquake of magnitude Mw=5.8 occurred on Cephalonia Island followed by a similar magnitude earthquake Mw=5.7 one week later on February 3, 2014. Extensive structural damages, landslides and many damages on the island’s main roads, harbour and airport caused mainly on the western and central part of the island. The fir...

26th IUGG GENERAL ASSEMBLY 2015 PRAGUE | CZECH REPUBLIC | JUNE 22 - JULY 2, 2015

We present results from four GPS campaigns in the broader Kaparelli– Asopos area in central Greece. This area is undergoing extension as demonstrated by seismological, geodetic and geological data. The east-west striking Kaparelli normal fault ruptured during the March 4, 1981, M = 6.3 earthquake and created km-long surface breaks with the down-thr...

Warning systems are key elements in disaster risk reduction. Today, early warning systems, based on rapid earthquake detection, facilitate towards taking urgent action to mitigate damages, prior to the arrival of strong ground motion and/or tsunami. However, even when this is not possible, considering the location of the earthquake source and the m...

Warning systems are key elements in disaster risk reduction. Today, early warning systems, based on rapid earthquake detection, facilitate towards taking urgent action to mitigate damages, prior to the arrival of strong ground motion and/or tsunami. However, even when this is not possible, considering the location of the earthquake source and the m...

The Volcanic and Geodynamic Field of the South Aegean Workshop May 20 – 22, 2015 Pyrgos, Santorini

The Aegean Sea is one of the most tectonically and seismically active areas in the world, thus constituting a Natural Laboratory. For the first time, a permanent multiparametric platform of networks that combine different (both terrestrial and space oriented) techniques, is established, in order to monitor the tectonic and volcanic activity in the...

Periods of unrest at caldera forming volcanic systems characterised by increased rates of seismicity and deformation are well documented. Some can be linked to eventual eruptive activity while others are followed by a return to quiescence. Here we use a 20-year record of InSAR and GPS measurements from Santorini volcano to further our understanding...

Modeling ionospheric disturbances behavior is a very challenging research issue which involves many non-linearities, dynamics and external factors. The optimal estimation of the ionospheric disturbances behavior is crucial in many Space and Earth science applications, including efficient Spaceborne Synthetic Aperture Radar (SAR) signal processing t...

Santorini is the most active volcano of the Hellenic Volcanic Arc (South Aegean Sea) and is best known for the Minoan eruption of the late Bronze Age. Dionysos Satellite Observatory of the National Technical University of Athens carried out gravity measurements during 1976. The latest campaign was carried out in December 2012 at selected locations...

This presentation explains the first ideas on how the future GNSS part of EPOS (European Plate Observing System) will be constructed.

Modeling the ionospheric disturbances behavior is of great importance in many Space-Geodetic applications, including robust Spaceborne Synthetic Aperture Radar (SAR) signal processing through accurate noise modeling and removal, 3D-monitoring of land and sea surface and geodynamics SAR Interferometry (InSAR) purposes. Estimating ionospheric disturb...

GPS rates based on data of an extended continuous and campaign-type GPS network in the North Aegean domain are presented. The data processed for the time period 1993–2009 is used to analyze the complex kinematic and deformation fields in the North Aegean Sea and adjacent regions. The presence of slowly deforming areas is investigated. Southern Bulg...

Recent studies have indicated that, for the first time since 1950, intense geophysical activity is occurring at the Santorini volcano. Extensive monitoring of the volcano with remote sensing techniques and extended geodetic measurements have quantified a period of unrest of the volcano which began in January 2011 and is shown to have diminished aro...

Santorini, a major caldera volcano in the South Aegean, entered a period of unrest in January 2011. This was characterised by the onset of detectable seismicity and caldera-wide uplift. For the past 360,000 years, the volcano has generated major explosive eruptions every 20,000 to 30,000 years, which are separated by phases during which andesite sh...

A joint approach using satellite techniques was applied to two different regions (Sellas and Chalkeio villages) of Peloponissos (Greece) in order to detect and monitor slope instability. In the context of the research effort, a GPS campaign network, along with one permanent GPS station and a corner reflector (CR) network, was established at each re...

The effective seakeeping performance of any watercraft is vital for safe navigation. Due to the long maritime tradition in Greece, the National Technical University of Athens (NTUA) has been a key player in developing tools and practices for conducting sea trials in open water. Since the introduction of the Mini-Ranger many years ago through to the...

A joint approach using satellite techniques was applied to two different regions (Sellas and Chalkeio villages) of Peloponissos (Greece) in order to detect and monitor slope instability. In the context of the research effort, a GPS campaign network, along with one permanent GPS station and a corner reflector (CR) network, was established at each re...

Recent studies have indicated that for the first time since 1950, intense geophysical activity is occurring at the Santorini volcano. Here, we present and discuss the surface deformation associated with this activity, spanning from January 2011 to February 2012. Analysis of satellite interferometry data was performed using two well-established tech...

Estimation of the ionospheric disturbances behavior is very important in many applications, including efficient Synthetic Aperture Radar (SAR) signal processing through accurate noise modeling and removal, monitoring of environmental evolution and geodynamics SAR Interferometry (InSAR) purposes. Modeling ionospheric disturbances behavior is a chall...

Santorini Volcano, the site of the catastrophic Minoan eruption in Greece, exhibits two distinct eruptive styles: small, effusive eruptions occur relatively frequently and build shields and domes of lava, whereas large explosive eruptions occur rarely, at intervals of 10,000–30,000 years. Both types of eruption were thought to incubate in a shallow...

Santorini Volcano, the site of the catastrophic Minoan eruption in Greece, exhibits two distinct eruptive styles: small, effusive eruptions occur relatively frequently and build shields and domes of lava, whereas large explosive eruptions occur rarely, at intervals of 10,000–30,000 years. Both types of eruption were thought to incubate in a shallow...

Land sliding, as a consequence of slope instability, constitutes a natural catastrophe resulting mainly from geological cause often followed by disastrous impact on both the natural and man-made environment. The reasons causing land slides can vary from purely geological factors, to other relevant or not natural catastrophes, urban or residential e...

In this work, the challenging task of forming cross-interferograms using ERS and ENVISAT satellite imagery is dealt with in detail, for the wider Athens metropolitan area. The main focus lies on the interpretation of the coherence map derived by suitable image pairs, in terms of both the imaging geometry and the underlying land cover of the area of...

eMACnet - the eastern Mediterranean Altimeter Calibration network, is the result of successful collaborative efforts in the Aegean area since the early 2000’s. Originally initiated with the Gavdos permanent absolute calibration facility and over the past four years with a second site at Kasteli, Crete, Greece, both of these sites in collaboration w...

A new set of geodetic velocities for Greece and the Aegean, derived from 254 survey-mode and continuous GPS sites, is used to test kinematic and dynamic models for this area of rapid continental deformation. Modeling the kinematics of the Aegean by the rotation of a small number (3–6) of blocks produces RMS misfits of ~5 mm yr−1 in the southern Aeg...

We present evidence that GPS velocity estimates of plate motions and fault slip rates agree to within uncertainties with geologic estimates during the most recent phase of the geologic evolution of the E Mediterranean region (post-Late Miocene). On this basis, we use the GPS differential velocities to estimate the timing of initiation of the princi...

This paper, published in Coordinates Vol. VI, Issue 5, May 2010 is an abridged version of the original version presented in the European Navigation Conference ENS-GNSS 2009 (4-6 May 2009) and published in the ENC-GNSS Proceedings. The paper presents new algorithms for rhumbline sailing (RLS) and great elliptic sailing (GES) calculations for route p...

This paper, published in Coordinates Vol. VI, Issue 5, May 2010 is an abridged version of the original version presented in the European Navigation Conference ENS-GNSS 2009 (4-6 May 2009) and published in the ENC-GNSS Proceedings. The paper presents new algorithms for rhumbline sailing (RLS) and great elliptic sailing (GES) calculations for route p...

The eastern Mediterranean altimeter calibration network (eMACnet) is the result of the expansion of ongoing collaborative efforts in the Aegean area over the past 10 years funded jointly by the EU, NASA, and regional governments. The initial efforts started with the collaboration with the Tech. Univ. of Crete at Chania, establishing stations on the...

This paper presents a software especially developed for the precise estimation of road horizontal and vertical geometric features, using the GPS/IMU data collected during the digital survey of road nets. The survey is based upon the geodetic positioning of a suitably equipped vehicle, moving along the road in a two way journey (forward/reverse). Fi...

This paper presents analytical methods and algorithms for the execution of accurate sailing calculations in a GIS environment (ECDIS and ECS), and in typical navigational receivers.

This paper presents simple contact formulas for the computation of the length of the meridian arc. The proposed alternative formulas are to be primarily used for accurate sailing calculations on the ellipsoid in a GIS environment as in ECDIS and other ECS. Their validity and effectiveness in terms of the accuracy achieved and the CPU time required...

The eastern Mediterranean altimeter calibration network (eMACnet) is the result of the expansion of ongoing collaborative efforts in the Aegean area. By 2003 we had established the Gavdos permanent absolute calibration facility, a joint EU, NASA, and the Swiss Federal Government effort. This was further expanded with NASA funding over the past thre...

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 a...

The Eastern Mediterranean forms the seismically most active region of the Alpine-Mediterranean plate boundary. It is characterized by the collision between the Eurasian and African plates. The collision is closely related to continental subduction and formation of the pronounced Hellenic trench system. In addition to the relatively slow CCW rotatio...

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 int...

The high precision of three to five years of continuous Global Positioning System (GPS) measurements at sites across the southern Aegean enable us to resolve two features of Aegean deformation that have, thus far, tended to be overlooked in favour of analyses of larger-scale regional motions. Firstly, we quantify the rate of extension across the re...

The rationalization of road asset management provides the tools and structure to set goals, identify priorities, advance processes, and measure results to demonstrate an improved performance of a road network. Under this framework, the Greek state initiated a major project for asset data collection in 1000 km of the national road network. The goal...

This paper presents the main recent results obtained by the seismological and geophysical monitoring arrays in operation in the rift of Corinth, Greece. The Corinth Rift Laboratory (CRL) is set up near the western end of the rift, where instrumental seismicity and strain rate is highest. The seismicity is clustered between 5 and 10 km, defining an...

On 7 September 1999 a magnitude M W 55.9 earthquake occurred in the Athens area of Greece producing a subsidence of 6–7 cm detected by radar interferometry. This study introduces a processing technique, which produces a clear deformation pattern of the earthquake, mostly released from artefacts due to orbital effects, unwrapping cycle slipping erro...

We Present a GPS-derived velocity field 1988-2005 for the zone of interaction of the Arabian African Nubian and Somalian and Eurasian plates The Velocity field indicates counterclockwise motion of a broad area of the Earth s surface that includes the Arabian plate adjacent parts of the Zagros and Central Iran Turkey and the Aegean at rates in the r...

Greece and the Aegean Sea form part of one of the most rapidly deforming areas of the Earth's surface and are characterized by a high level of intra-plate seismicity in comparison to neighboring regions. AEGEANET is a geodetic network that we have established in order to consistently measure the geodetic strain in the broader Aegean Sea region, inc...

In respect of the great Sumatra-Andaman earthquake and subsequent tsunami of 26 December 2004, the study of coupling at subduction zones is imperative to understanding the seismic—or otherwise—hazard posed to a region. The Mediterranean Sea includes the Hellenic subduction zone, which accommodates the ~35 mm/yr of convergence between the oceanic li...

Internal soil erosion, hydraulic gradients and stability problems resulting from high pore pressures are common causes of failure of embankment dams. However, the self-weight of a dam and variations in water pressure (resulting from the annual variation in water volume) may be a source of extensive deformation of its embankment and foundation that,...

The Hellenic subduction zone accommodates the convergence between the oceanic lithosphere of the African plate and the extending continental lithosphere of the Aegean. Former studies (e.g. Jackson & McKenzie, 1988) concluded that earthquakes can only account for 10% of the relative motion, suggesting that the subduction is in a stable sliding state...

SUMMARY In this project, a method to extract tectonic activity - induced vertical displacements from InSAR along one-dimensional features (roads, pipelines, aqueducts), is presented and the reliability of this method is evaluated. The evaluation is performed by a comparison of In- SAR results and terrestrial surveying. The test field is in the nort...

GPS (Global Positioning System) data collected in the Corinth Rift during eleven campaigns between 1990 and 2001 provide velocities of 57 points with ∼1.5 mmyr−1 accuracy. Peloponnesos moves at 30 mmyr−1 to the N215° E with respect to a fixed Europe. Extension across the rift is accommodated in a narrow band offshore. Its rate increases from east t...

GPS (Global Positioning System) data collected in the Corinth Rift during eleven campaigns between 1990 and 2001 provide velocities of 57 points with ˜1.5 mm yr-1 accuracy. Peloponnesos moves at 30 mm yr-1 to the N215° E with respect to a fixed Europe. Extension across the rift is accommodated in a narrow band offshore. Its rate increases from east...

This study presents the Ionospheric Total Electron Content (TEC) response during two recent magnetic storms. A mathematical approach based on the observations of the permanent Global Positioning System (GPS) station at Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) was used to obtain temporal evolution of...

The accuracy achieved by permanent GPS networks now allows the detection of strain rate as small as 1 mm/yr over hundreds of kilometres, providing new constraints on how continental domains deform. In this study, we derive a new geodetic velocity field for Europe and the Mediterranean by rigorously combining (1) a selection of ITRF2000 sites, (2) a...