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Publications (100)
Context. Gravitational waves from black-hole (BH) merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models – and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are...
Geoscientists make huge efforts in order to develop techniques by the use of real-time predictive and analytical methods, in order to achieve better planning for constructions, Earth exploitation and prevention of natural hazard. A newly emerging approach for understanding remote sensing data, which is gradually becoming widely available, comes by...
In this work, very deep super-resolution (VDSR) method is presented for improving the spatial resolution of remotely sensed (RS) images for scale factor 4. The VDSR net is re-trained with Sentinel-2 images and with drone aero orthophoto images, thus becomes RS-VDSR and Aero-VDSR, respectively. A novel loss function, the Var-norm estimator, is propo...
Deep learning techniques are applied so as to increase the spatial resolution of Sentinel2 satellite imagery, depicting the Amynteo lignite mine in Ptolemaida, Greece. Resolution enhancement by factors 2 and 4 as well as by factors 2 and 6 using Very-Deep SuperResolution (VDSR) and DSen2 networks, respectively, provides fairly well results on Amynt...
Artificial Neural Networks (ANN) are mathematical computing paradigms imitating the operations of biological neural systems. Their nonlinear nature and ability to learn from the environment make them highly suited to solve real-world problems from those that are still under development. In the field of Physics there are many problems which cannot b...
We investigate Titan's low- and mid-latitude surface using spectro-imaging near-infrared data from Cassini/VIMS. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite...
The detailed three-dimensional modeling of buildings utilizing elevation data, such as those provided by light detection and ranging (LiDAR) airborne scanners, is increasingly demanded today. There are certain application requirements and available datasets to which any research effort has to be adapted. Our dataset includes aerial orthophotos, wit...
In a great variety of applications, such as real-time robot localization and visual navigation, architectural design, 3D city reconstruction, building recognition in urban environments is required. In this work a comparative study of visual feature extraction methods for building retrieval on urban databases is performed. To this end, a database of...
Urban density is an important factor for several fields, e.g. urban design, planning and land management. Modern remote sensors
deliver ample information for the estimation of specific urban land classification classes (2D indicators), and the height of urban land
classification objects (3D indicators) within an Area of Interest (AOI). In this rese...
Nowadays there is an increasing demand for detailed 3D modeling of buildings using elevation data such as those acquired from LiDAR airborne scanners. The various techniques that have been developed for this purpose typically perform segmentation into homogeneous regions followed by boundary extraction and are based on some combination of LiDAR dat...
We investigate the nature and possible formation processes of three areas on Titan's surface which have been suggested as geologically interesting: Hotei Regio, Tui Regio and Sotra Patera. We also re-analyze the spectral characteristics of the Huygens Landing Site. We apply a statistical Principal Component Analysis (PCA) and a radiative transfer (...
Building detection has been a prominent area in the area of image classification. Most of the research effort is adapted to the specific application requirements and available datasets. In this paper we present a comparative analysis of different classification techniques for building block extraction. Our dataset includes aerial orthophotos (with...
We present a study on Titan's possibly cryovolcanic and varying regions
as suggested from previous studies [e.g. 1;2;7]. These regions, which
are potentially subject to change over time in brightness and are
located close to the equator, are Tui Regio, Hotei Regio, and Sotra
Patera. We apply two methods on Cassini/VIMS data in order to retrieve
the...
We present a study of Titan's complex geology with a focus on the
satellite's surface regions that are showing spectral variations with
time possibly linked to geological activity. We apply a statistical
method, the Principal Component Analysis (PCA) [1] and a radiative
transfer method (RT) [1,2] on three potentially 'active' regions on
Titan, i.e....
The Cassini Visual and Infrared Mapping Spectrometer (VIMS) obtained
data of Titan's surface from flybys performed during the last eight
years. In the 0.8-5.2 µm range, these spectro-imaging data showed
that the surface consists of a multivariable geological terrain hosting
complex geological processes. The data from the seven narrow methane
spectr...
Spectro-imaging and radar measurements by the Cassini-Huygens mission
suggest that some of the Saturnian satellites may be geologically active
and could support tectonic processes. In particular, Titan, Saturn's
largest moon, possesses a complex and dynamic geology as witnessed by
its varied surface morphology resulting from aeolian, fluvial, and
p...
We present a study of Titan's geology with a view to enhance our current
understanding of some particular regions on the satellite's surface,
which may be varying in brightness and/or in color etc. We apply here a
statistical method, the Principal Component Analysis (PCA) [1] and a
radiative transfer code (RT) [1,2] on three such potentially "activ...
We present a study of Titan's geology with a view to enhance our current
understanding of the satellite's potentially geologically varying
regions. We apply here a statistical method, the Principal Component
Analysis (PCA) [1, 2] and a radiative transfer method [3, 1] on three
potentially "active" regions on Titan, i.e. regions possibly subject to...
The satellites of Jupiter and Saturn have been revealed as extremely
astrobiologically interesting bodies presenting promising conditions for
habitability and the development and/or maintenance of life. Titan and
Enceladus, Saturn's satellites, were found by the Cassini-Huygens
mission to possess active organic chemistries with seasonal variations,...
The Cassini Visual and Infrared Mapping Spectrometer (VIMS) obtained
data of Titan's surface from flybys performed during the last seven
years. In the 0.8-5.2 µm range, these spectro-imaging data showed
that the surface consists of a multivariable geological terrain hosting
complex geological processes. The data from the seven narrow methane
spectr...
Titan, Saturn's satellite, is one of the most interesting planetary
bodies in the Planetary Geology domain. Spectro-imaging and radar
measurements by the Cassini-Huygens, joint ESA/NASA mission, suggest
that it may be geologically active and could support tectonic processes.
In particular, Titan possesses a complex and dynamic geology as
witnessed...
People have always been charmed by the beauty of the starry sky, the
Sun, the Moon, the planets, the Solar System and the mystery of the
birth and the evolution of the Cosmos. As the deep space is believed to
be the only territory unexplored by the mankind, the humanity has always
been looking forward to the discoveries of Space Science. However, d...
The Cassini Visual and Infrared Mapping Spectrometer (VIMS) obtained data of Titan's surface from flybys performed during the last seven years. In the 0.8-5.2 µm range, these spectro-imaging data showed that the surface consists of a multivariable geological terrain hosting complex geological processes. The data from the seven narrow methane spectr...
Cassini synthetic aperture radar (SAR) images of Titan, the largest
satellite of Saturn, reveal surface features with shapes ranging from
quasi-circular to more complex ones, interpreted as liquid hydrocarbon
deposits assembled in the form of lakes or seas. One of the major
problems hampering the derivation of meaningful texture information from
SA...
The Synthetic Aperture Radar (SAR) instrumentation on board the Cassini orbiter has identified large hydrocarbon liquid deposits on the surface of Titan [e.g. 1], distributed mainly around its northern polar regions. Recent studies [2] suggest that the rims of these structures display seasonal changes, where the lakes appear to be shrinking. Howeve...
We present a study of Titan's geology with a view to enhance our current
understanding of the satellite's potentially active zones. We combine
here Principal Component Analysis and "atmosphere substraction" [1;2],
as a prelude to "differential spectroscopy" on three potentially active
regions on Titan, namely Tui Regio, Hotei Regio, and Sotra Facul...
The icy satellites around Jupiter and Saturn have been revealed as
recently or presently active bodies of high interest for geology and
astrobiology. Several of them show promising conditions for internal
structures involving liquid water oceans. The surface features observed
on Jupiter's Europa and Ganymede as well as Saturn's Titan and Enceladus...
Saturn's largest satellite Titan is one of the most interesting
planetary bodies. Since 2004 it is being explored by the Cassini-Huygens
joint ESA/NASA mission, whose results indicate that it might be
geologically active and may support local tectonic processes. Titan
possesses a dynamic, multivariable and Earth-like (albeit with different
material...
A filtering technique is applied to obtain the restored synthetic
aperture radar (SAR) images. One of the major problems hampering the
derivation of meaningful texture information from SAR imagery is the
speckle noise. It overlays "real" structures and causes gray value
variations even in homogeneous parts of the image. Our method, the TSPR
(total...
The icy moons of the Outer Solar System are extremely interesting planetary bodies since they possess evidence about the origin and evolution of their systems and the Solar System in general. In terms of surface morphology, internal structure as well as their environmental uniqueness, Saturn's moons Titan and Enceladus and Jupiter's Europa and Io a...
The exploration of the systems of the outer planets of the Solar System, in particular Jupiter and Saturn, is in the forefront of contemporary space exploration. Indeed, these two planetary systems host extreme environments which can provide us with information on the origin and evolution and the interactions therein. The major satellites of these...
The determination of Titan's surface chemical composition is critical in order to understand its geology and investigate the interactions between the interior, the surface and the atmosphere. Cassini/VIMS acquired many spectral images taken within the seven atmospheric methane windows (where the methane absorption is weak) that revealed the complex...
Astronomy is the oldest natural science that contributed enormously to the human history and the development of civilizations globally. Without doubt, following the heritage of their ancestors, space scientists offer also nowadays with many spin-offs. Besides, celestial observations, as long as space exploration, can provide the layman public with...
Observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS) in 352 wavelengths show two anomalously bright and possibly geologically active regions on Titan, Tui Regio and Hotei Regio. Both features are imaged in narrow spectral windows centered at 0.93, 1.08, 1.27, 1.59, 2.03, 2.8 and 5 µm, through Titan's dense atmosphere. Despi...
Since 2004, investigations, measurements and data analysis by the Cassini-Huygens mission showed that Titan, Saturn's largest satel-lite, presents complex, dynamic and Earth-like geology. Endogenous, as well, as exogenous dynamic processes, have created diverse terrains with extensive ridges and grooves, impact units, caldera-like structures, layer...
Continuing investigations of Titan's surface have shown that this Earth-like Saturnian satellite presents an extremely complex geology [1, 2, 3]. The Cassini Mission Visual and Infrared Mapping Spectrometer (VIMS) acquires data operating as a multi-spectral camera that allow for a complete analysis of the composition, geology and morphology of Tita...
Synthetic Aperture Radar (SAR) images of Titan, the largest satellite of Saturn, reveal quasi-circular to complex features which are interpreted to be liquid hydrocarbon lakes. One of the major problems hampering the derivation of meaningful texture information from SAR imagery is the speckle noise. It overlays real structures and causes gray value...
Cassini carries a multimode Ku-band (13.78 GHz) radar instrument designed to probe the surface of Titan and that of other targets in the Saturn system in four operating modes: imaging, altimetry, scatterometry, and radiometry. The Synthetic Aperture Radar (SAR) mode is used at altitudes under ~4000 km, resulting in spatial resolution ranging from ~...
Saturn's satellites Titan and Enceladus are few of the most interesting
planetary bodies in the Comparative Planetology domain. Both satellites
have been and are still explored by the Cassini-Huygens joint ESA/NASA
mission, launched in 1997. In particular, Titan is the second largest
moon in the Solar System, with an earth-like atmosphere and a lan...
We present our study on Titan's geology in order to develop our current
understanding of the satellite's active zones [1],[2]. The key aim is to
study Titan's geology holistically, by means of internal activity and
surface properties, in addition to terrestrial comparisons. We have
applied the Principal Components Analysis (PCA) method in order to...
The framework of this study is focused on automatic fast recognition of agricultural interest for TerraSAR-X images. The intended goal is to label regions in an image as fast as possible, into classes significant for a given application, like crop classification. First, a filtering technique is applied to obtain the restored image. Then, two differ...
The photo-gravitational problems of two or more bodies have attracted much attention during the last decades. In this paper,
radiation is considered as an additional factor influencing the particle motion in a regular polygon formation of N big bodies
where the ν=Ν−1 primary bodies have equal masses and are located at the vertices of a regular poly...
The distribution of spectral types in extended stellar systems in galaxies can be a powerful mine of information regarding:
1. not only the properties of the stellar content (such as age, composition) but also
2. the spatial distribution of certain types in order to trace specific structures (such as star forming regions and their geometry)
Objecti...
Stellar spectral classification is not only a tool for labeling individual stars but is also useful in studies of stellar population synthesis. Extracting the physical quantities from the digitized spectral plates involves three main stages: detection, extraction, and classification of spectra. Low-dispersion objective prism images have been used a...
In this article we study the N83-84-85 region of the inner wing of the SMC. Direct and low-dispersion objective prism plates taken with the 1.2m UK Schmidt Telescope have been digitized by the SuperCOSMOS machine. Star counts have been performed for our region in selected luminosity slices in the U filter and isodensity contours have been used to i...
There are 509 expanding neutral hydrogen shells catalogued in the Small Magellanic Cloud (SMC), all apparently very young, with dynamical ages of a few Myr. To examine their relationship with young stellar objects we cross-correlated the shell catalogue with various catalogues of OB associations, super giants, Cepheids, WR stars, supernova remnants...
In this article we study the N83-84-85 region of the inner wing of the SMC. Direct and low-dispersion objective prism plates taken with the 1.2 m UK Schmidt Telescope have been digitized by the SuperCOSMOS machine. Star counts have been performed for our region in selected luminosity slices in the $U$ filter and isodensity contours have been used t...
A method for speckle reduction and segmentation of synthetic aperture radar (SAR) images is presented here. As a first step we consider a preclassification to a specific number of labels (classes). The second step (final classificatio) is the relaxation labeling process. The method can be considered as a fast unsupervised technique. We have worked...
An iterative filter that can be used for speckle reduction and restoration of synthetic aperture radar (SAR) images is presented here. This method can be considered as a first step in the extraction of other important information. The second step is the detection of high-reflectance regions and continues with the segmentation of the total image. We...
In this paper we describe an approximation of speckled image observation (attachment to data) laws by generalized Gaussian pdfs. We use Kullback-Leibler (KL) divergence (entropy) for this purpose. This leads to a mathematical model which can be useful for speckled image restoration and for related hyperparameter estimation.
We have acquired new images of Titan in 2002 using the CFHT adaptive optics system PUEO, in Hawaii. With the infrared camera KIR, we have covered the 0.8-2.5 micron range on Titan using narrow-band filters during four nights in November 2002 (covering both the GEE and the GWE with seeing less than 0.6") thus gathering very good resolution data on T...
We have acquired new images of Titan using the adaptive optics system PUEO located at the CFHT in Hawaii. Combined with the infrared camera KIR, we have covered the near-infrared range on Titan using several new narrow-band filters covering the methane bands (pertaining to the atmosphere) and the so-called methane "windows" (containing both atmosph...
A generalized Gaussian model that can be used for speckle reduction and restoration of synthetic aperture radar (SAR) images is presented here. We have worked in 3-look simulated and real ERS-1 amplitude images. A MAP approximation of the a posteriori log-likelihood distribution is given and the results of a local deterministic estimator are presen...
An iterative optimization algorithm which can be used for speckle reduction and segmentation of synthetic aperture radar (SAR) images is presented here. This method contains as a first step a fast restoration and as a second one the segmentation.
We have worked in 3-look simulated and real ERS-1 amplitude images. The iterative filter is based on a...
A speckle reduction method for synthetic aperture radar (SAR) images is presented here. This method can be considered as a first step for the extraction of other important information. The second one is the detection of high reflectance regions which yields an important step to continue the segmentation of the total image. We have worked in 3-look...
In our observations of Titan with the CFHT/PUEO adaptive optics system,
besides the well-known Titan smile (or north-south asymmetry observed
usually), our 1998 J2 and H2 images (of remarkable quality due to a
seeing of 0.35 arcsec) showed a 10-17% brighter western than eastern
limb, that we interpreted as a first detection of possible diurnal
effe...
The success of Richardson-Lucy (RL) algorithm is that it forces the restored image to be non-negative and to conserve global ux at each iteration. The problem with RL algorithm is that it produces solutions that are highly unstable, with high peaks and deep valleys. Our aim is to modify RL algorithm in order to regularize it while preserving positi...