Vassilia Karathanassi

Vassilia Karathanassi
National Technical University of Athens | NTUA · School of Rural and Surveying Engineering

PhD

About

121
Publications
29,210
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1,534
Citations

Publications

Publications (121)
Article
Sentinel-2 (S2) images have been used in several projects to detect large accumulations of marine litter and plastic targets. Their limited spatial resolution though hinders the detection of relatively small floating accumulations of marine debris. Thus, this study aims at overcoming this limit through the exploration of fusion with very high-resol...
Article
Full-text available
A significant amount of the produced solid waste reaching the oceans is made of plastics. The amount of plastic debris in the ocean and coastal areas is steadily increasing and is now a major global environmental issue. The monitoring of marine plastic litter, ground-based monitoring systems and/or field campaigns are time-consuming, expensive, req...
Article
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Observing phenological changes are important for evaluating the natural regeneration process of forests, especially in Mediterranean areas where the regeneration of coniferous forests depends on seeds and the changes in blossoming time are influenced by climate change. The high temporal resolution of Sentinel-1 data allows the time series analysis...
Preprint
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The modernization of the Common Agricultural Policy (CAP) requires the large scale and frequent monitoring of agricultural land. Towards this direction, the free and open satellite data (i.e., Sentinel missions) have been extensively used as the sources for the required high spatial and temporal resolution Earth observations. Nevertheless, monitori...
Article
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Change detection (CD) through Earth observation techniques can offer very significant information for monitoring tasks in a time-efficient manner. Very high-resolution (VHR) images can display objects in fine detail, thus making it possible to rapidly perceive isolated changes. However, this is a challenging task because of the increased within-cla...
Article
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This study aims to investigate how alternations of the land surface temperature (LST) affects the normalized difference vegetation index (NDVI) in Paphos forest, Cyprus, using Landsat-5 and Landsat-8 imagery for the time periods 1993–2000 and 2013–2018, respectively. A total of 262 Landsat images were processed to compute the mean monthly NDVI and...
Article
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A new automatic, free and open-source python toolbox for the mapping of floodwater is presented. The output of the toolbox is a binary mask of floodwater at a user-specified time point within geographical boundaries. It exploits the high spatial (10m) and temporal (6 days per orbit over Europe) resolution of Sentinel-1 GRD intensity time series and...
Preprint
Full-text available
Effective and efficient control of the agrarian obligations imposed by the Common Agricultural Policy (CAP) and the high-level decision making for national and global food security, requires systematic and timely monitoring of the agricultural land. In this study we focus on rice paddy monitoring in South Korea to ultimately deliver food security r...
Article
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Cultural Heritage (CH) is a domain which has been greatly affected by climate change in the past decades. At the same time Information and Communication Technologies (ICT) have been greatly exploited to contribute to the holistic documentation, to support conservation and preservation actions. In order to move further on from the interdisciplinary...
Poster
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In this study, we present a wavelet-based approach to explore the connections of each driving factor with ground deformation results from interferometric SAR. Youtube presentation at: https://www.youtube.com/watch?v=zt2IjzAjbx4
Article
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Hyperspectral PRISMA images are new and have not yet been evaluated for their ability to detect marine plastic litter. The hyperspectral PRISMA images have a fine spectral resolution, however, their spatial resolution is not high enough to enable the discrimination of small plastic objects in the ocean. Pansharpening with the panchromatic data enha...
Article
Full-text available
During the last decades, massive amounts of satellite images are becoming available that can be enriched with semantic annotations for the creation of value-added Earth Observation products. One challenge is to extract knowledge from the raw satellite data in an automated way and to effectively manage the extracted information in a semantic way, to...
Article
Full-text available
This study seeks to test the predictive performance of a hydraulic model using as reference the flood extent extracted through Sentinel-1 imagery. A precipitation event which took place between the 22nd and 28th of February 2018 in Pineios river basin, Central Greece, was analyzed. A threshold technique was performed to delineate the inundation ext...
Conference Paper
Full-text available
Cloud contamination represents a large obstacle for mapping the earth’s surface using remotely sensed data.Therefore, cloudy pixels should be identified and eliminated before any further data processing can be achieved.Although several threshold, multi-temporal and machine learning applications have been developed to tackle this issue, it still rem...
Article
Full-text available
Marine monitoring constitutes one of the main thematic areas of the Sentinel mission. The Sentinel 3 OLCI (S3) sensor provides satellite data for services relevant to the ocean and land. While the spatial resolution of S3 images (300m) is suitable for most marine applications, there are some applications such as floating debris detection, suspended...
Article
Full-text available
Removal of cloud interference is a crucial step for the exploitation of the spectral information stored in optical satellite images. Several cloud masking approaches have been developed through time, based on direct interpretation of the spectral and temporal properties of clouds through thresholds. The problem has also been tackled by machine lear...
Article
Full-text available
Time Series Interferometric Synthetic Aperture Radar (TSInSAR) methods have been widely and successfully applied for spatiotemporal ground deformation monitoring. The main groups of methodological approaches are often referred to as Persistent Scatterer (PS), Small Baseline (SB), and hybrid approaches that incorporate PS and SB concepts. While TSIn...
Article
Cloudy regions in optical satellite images prevent the extraction of valuable information by image processing techniques. Several threshold, multi-temporal and machine learning approaches have been developed for the separation of clouds in land and ocean applications, but this task still remains a challenge. Concerning deep water marine application...
Data
This dataset includes 2.133.324 reflectance water spectra which were manually extracted by visual observation from 30 Sentinel 2 level 1C satellite images. The spectra were extracted from deep water areas with high noise levels and sunglint. The Sentinel 2 images depicted 2 tiles of the same orbit and were collected in 2016 (2 images), 2017 (19 ima...
Chapter
The use of airborne imaging spectrometers has become increasingly popular in the past few years. In order to eliminate spectral distortions in hyperspectral data, regular spectral recalibration of the sensor is needed, but this is not always possible due to the high cost and the time needed. One important spectral distortion is spectral smile. Seve...
Conference Paper
SENTINEL-2 (S2) is a European wide-swath, high-resolution, multi-spectral imaging mission consisting of two twin satellites with a high revisit frequency that contributes to ongoing multispectral observations and enhances Copernicus services and applications such as continuous coverage of overseas and oceans with the production of global maps of ph...
Conference Paper
Full-text available
This paper illustrates the capabilities of distributed scatterer satellite Synthetic Aperture Radar Interferometry (InSAR) to monitor time-varying land deformation on mines. Due to continuous mining activities, monitoring ground deformation in and around mine areas has great importance to prevent possible slope instabilities that may lead to consid...
Conference Paper
Full-text available
Fronts, which are sharp boundaries between distinct water masses, play a substantial role in managing biodiversity of marine species and preserving a resilient ecosystem. The overarching aim of this study is to compare different methodologies for detecting marine fronts. Many marine fronts are identifiable by their strong temperature gradient. For...
Article
The aim of this study is to investigate the potential of Sentinel-2 imagery for the identification and determination of forest patches of particular interest, with respect to ecosystem integrity and biodiversity and to produce a relevant biodiversity map, based on Simpson’s Diversity Index in Taxiarchis university research forest, Chalkidiki, North...
Article
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Two object-based image analysis methods are developed for detecting oil spills from known natural outflows as well as light oil spill events using Sentinel 2 imagery. The methods are applied to Sentinel 2 images of a known area of natural oil outflow as well as on a Sentinel 2 image of a recent oil spill event along the south coast of Athens, Greec...
Article
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Coastal zones are vulnerable to erosion and loss by level sea rise. Subsidence caused by the reduction of fluvial sediments in coastal zones found close to dams, is another important deformation factor. Quantification of the deformation rate of coastal region is essential for natural and anthropogenic activities. The study utilizes Interferometric...
Article
Full-text available
In this study the usefulness of the ALOS optical and radar data for landslide monitoring is examined. ALOS contains three sensors, commonly referred to as the “three eyes” of ALOS. These sensors are: the Panchromatic Remote-Sensing Instrument for Stereo Mapping (PRISM), the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2), and the Pha...
Article
Carbon sequestration service of Mediterranean forest and other wooded land is threatened by their fragile, complex, and highly evolving nature, due to both human disturbances and climate change. Remote-sensing methods for forest biomass estimation have gained increased attention, and substantial research has been conducted worldwide over the past f...
Conference Paper
The accuracy of InSAR DEMs is affected by the temporal decorrelation of SAR images which is due to atmosphere, land use/cover, soil moisture, and roughness changes. Elimination of the temporal decorrelation of the master and slave image improves the DEMs accuracy. In this study, the Independent Component Analysis was applied before interferometric...
Article
Full-text available
In this study, a method called K -F for reducing the filtering effects on the interferometric phase signal is proposed. The method relies on the well-known parametric model for implementing noise reduction, while maintaining a low level of information loss. Relationships between the estimated interferometric information and noise reduction have bee...
Article
In this study, a method called K -F for reducing the filtering effects on the interferometric phase signal is proposed. The method relies on the well-known parametric model for implementing noise reduction, while maintaining a low level of information loss. Relationships between the estimated interferometric information and noise reduction have bee...
Article
Full-text available
This paper introduces a novel distance-based method, for estimating the number of endmembers and extracts them. The method adopts the network concept according to which, every pixel of the image creates a network. The endmembers and the pixel are the nodes of the network while the fractional distance parameter describes and quantifies it. When the...
Conference Paper
Full-text available
This paper proposes an efficient methodology for combining multiple remotely sensed imagery, in order to increase the classification accuracy in complex forest species mapping tasks. The proposed scheme follows a decision fusion approach, whereby each image is first classified separately by means of a pixel-wise Fuzzy-Output Support Vector Machine...
Conference Paper
Full-text available
In this study, a method for reducing the filtering effects on the interferometric phase signal is proposed. Theoretical analysis showed that while noise reduction is maximized after filtering, the loose of interferometric phase signal is also maximized. This state has been also verified by observations on SAR interferometric data where pixels with...
Presentation
Full-text available
This paper proposes a methodology for estimating aboveground forest biomass through remotely sensed data, acquired from both active and passive sensors. The study focuses on a Mediterranean forest ecosystem in northern Greece. Four dominant species have been considered, namely, Hungarian oak (Quercus frainetto), European beech (Fagus sylvatica s.l....
Conference Paper
Full-text available
In recent years, many efforts have been made in order to assess forest stand parameters from remote sensing data, as a mean to estimate the above-ground carbon stock of forests in the context of the Kyoto protocol. Synthetic aperture radar interferometry (InSAR) techniques have gained traction in last decade as a viable technology for vegetation pa...
Conference Paper
Full-text available
This paper presents a new method for automatically determining the optimum regression model, which enable the estimation of a parameter. The concept lies on the combination of k spectral pre-processing algorithms (SPPAs) that enhance spectral features correlated to the desired parameter. Initially a pre-processing algorithm uses as input a single s...
Article
The hydrological network analysis was based for many years on topographic maps or on aerial photos. The evolution of GIS software and the existence of plenty of satellite sensors collecting data with high spatial resolution made possible the creation of quite accurate Digital Surface Models (DSM) and the automatic drainage extraction. In this study...
Article
Cast shadows caused by sparse clouds usually degrade spaceborne and airborne imagery. They result from the decrease of the direct solar beam due to the presence of a non-transparent cloud. The reduction of the downwelling solar flux density can be quantified during an air campaign, if the aircraft flies beneath the cloud and is equipped with an add...
Conference Paper
Full-text available
In spectral unmixing theory, data reduction techniques play an important role as hyperspectral imagery contains an immense amount of data, posing many challenging problems such as data storage, computational efficiency, and the so called "curse of dimensionality". Feature extraction and feature selection are the two main approaches for dimensionali...
Article
For each pixel, the values of the unwrapped phase produced by interferometric pairs can be parameterized and phase components, such as height, atmospheric path delay difference for the dates of every interferometric set image acquisition, and unwrapping error can be estimated through the solution of a rank deficient system of equations. There are s...
Article
This paper introduces a novel approach for estimating the numbers of endmembers in hyperspectral imagery. It exploits the geometrical properties of the noise hypersphere and considers the signal as outlier of the noise hypersphere. The proposed method, called outlier detection method (ODM), is automatic and non-parametric. In a principal component...
Article
Full-text available
Hyperspectral remote sensing exploits the optical properties of materials and provides detailed information about them. From a theoretical point of view, in case of oil spills, it cannot only detect and delineate them, but also provide information about the oil type and oil thickness, significantly contributing at the remediation stage of clean-up....
Article
Full-text available
The concept of a relative radiometric normalization (RRN) for multitemporal multispectral and hyperspectral images is investigated. A new automatic RRN methodology is presented: the Normalized Proximity and Similarity Methodology (NPSM). The NPS methodology introduces two spectral metrics, the absolute normalized difference (AND) and the absolute n...
Article
Full-text available
Physically based atmospheric correction is one of the most important but also perilous radiometric corrections in remote-sensing imagery. The main objective of this work was to evaluate the efficiency of atmospheric correction algorithms, based not only on quantification of the changes induced but also on a step-by-step interpretation of the result...
Article
Full-text available
This application paper demonstrates the capabilities of multispectral remote sensing images on detecting oil spills and underwater natural oil outflows in oil potential areas. An object based method for oil spill detection using high or very high multispectral images has been developed. The method exploits the knowledge provided by the systematic p...
Article
In the hyperspectral theory, data reduction techniques play an important role in the classification processing as hyperspectral imagery contains an immense amount of data posing many challenging problems such as data storage, computational efficiency, and the curse of dimensionality. Hyperspectral band selection technique is a well-known dimensiona...
Article
Full-text available
A new unsupervised classification approach for polarimetric synthetic aperture radar (POLSAR) data is proposed in this paper. The Wishart-Chernoff distance is calculated and used in an agglomerative hierarchical clustering approach. Initial segmentation of POLSAR data into clusters is obtained based on the total backscattering power (SPAN) combined...
Conference Paper
Full-text available
This paper presents a new methodology for the discrimination of plant species and their varieties using hyperspectral data. The concept lies on the combination of spectral pre-processing algorithms (SPPA) that enhance spectral discrimination between species and their varieties. SPPA use as input a single spectral signature and transform it accordin...
Article
Full-text available
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 s...
Conference Paper
Η Βελτίωση των φυτών ως τέχνη και επιστήμη βασίζεται στη διαφορετικότητα των ατόμων όπως αυτή εκφράζεται φαινοτυπικά εξαιτίας της αλληλεπίδρασης του γενότυπου με το περιβάλλον. Με δεδομένο ότι η αφαίρεση των επιδράσεων του περιβάλλοντος είναι εξαιρετικά δύσκολη, τα αποτελέσματα της φαινοτυπικής έκφρασης δεν είναι απόλυτα αντικειμενικά ώστε να εξασφ...
Conference Paper
This paper presents a new methodology for automatically labeling extracted endmembers from hyperspectral images, using a reference Spectral Library (SL). The SL is structured with three main layers: main consisting material, semantic meaning, and illumination conditions in order to classify the endmembers. The labeling process is based on two simil...
Conference Paper
The majority of the existing unmixing methods use a unique set of endmembers for spectral mixture analysis of the entire image, failing to account that each pixel may be comprised of a different combination of endmembers. Multiple endmember spectral mixture analysis (MESMA) allows the number and types of endmembers to vary on a per-pixel basis. The...
Conference Paper
Knowing the number of endmembers in a hyperspectral image is a prerequisite for almost all the endmember extraction algorithms and plays a key role for the accuracy of the spectral unmixing. Moreover, in case of data compression, it is important to know the number of endmembers in order to define the appropriate signal subspace. In this paper, a ne...
Conference Paper
Waste management is one of the most critical environmental concerns. SAR interferometry has been widely used in studies related to ground subsidence or ground deformation but it is hardly found in landfill monitoring and waste management applications. In this study the potential of repeat pass SAR interferometry is investigated for extracting addit...
Conference Paper
The last two decades, SAR interferometry is used in order to produce Digital Elevation Model (DEM) for wide areas. However, the DEM produced by only one interferometric pair is characterized by low accuracy, due to several parameters that affect the final result. In this study the improvement of the DEM accuracy is attempted through the production...
Article
This research focuses on the investigation of remote-sensing techniques for the detection of coastal sub-aerial springs and submarine groundwater discharges using airborne thermal and hyperspectral imagery. Very high spatial resolution thermal and hyperspectral images were acquired using Thermal Airborne Broadband Imager 320 (TABI-320) and Compact...
Article
Full-text available
Abstract: This article describes metrics in order to quantify landscape structure. Landscape metrics are offered and designed to be as versatile as possible using several programs. In this paper it is attempted to (a) collect all the metrics found in the literature, (b) classify them, and (c) evaluate them through their use. An extensive investigat...
Article
Full-text available
PARCHARIDIS, I.; KOURKOULI, P.; KARYMBALIS, E.; FOUMELIS, M., AND KARATHANASSI, V., 0000, Time series synthetic aperture radar interferometry for ground deformation monitoring over a small scale tectonically active deltaic environment (Mornos, Central Greece). Journal of Coastal Research, 00(0), 000–000. West Palm Beach (Florida), ISSN 0749-0208. T...