Contribution of GPS and GIS assisted spaceborne remote sensing in the morphotectonic research of Central Macedonia (N. Greece)

Earth Observation from space is nowadays an important activity of the European Union within its environmental policies. In this context, spaceborne Remote Sensing has been attracting an increasing attention among the scientific community. In the last few decades, the rapid evolution of space technology has significantly contributed to the recognition of Remote Sensing as an important tool and source of information for Geoscience applications. At the same time, new techniques and advanced capabilities of digital processing of remote sensing data, along with additional technologies such as Geographical Information Systems (GIS) and Global Navigation Satellite Systems (GNSS), have established unprecedented capabilities of collection, synthesis, analysis and representation of extremely inhomogeneous data and information. Among many other implications, this has lead to impressive results regarding the digital representation of the Earth’s relief and the mapping of several geodynamical phenomena. This thesis deals with the contribution of spaceborne Remote Sensing in Geosciences, with emphasis on: (1) the synergy with GIS and GNSS, (2) the topographic-geodetic components of Remote Sensing, with the implementation of SAR Interferometry (InSAR) techniques and (3) the evaluation of Remote Sensing methods and data, such as satellite images, Digital Elevation Models/DEMs and GPS data. The application area primarily concerns the fields of Geomorphology, Morphotectonics and Seismotectonics. In this context, the purpose of the analyses carried out was the processing of satellite data and images of various spatial and spectral resolution (ENVISAT/ASAR, ERS, TerraSAR-X, SPOT-5, LANDSAT) as well as the use and validation of DEMs from various sources (SRTM, GDEM, InSAR etc), in order to study areas in Central Macedonia (Northern Greece). Special attention is given to the broader area of Mygdonia basin (Geomorphology and Morpho-Seismotectonis), the city of Thessaloniki and the broader Kalohori area (subsidence phenomena). The results and conclusions of this study are related to new information about subsidence and deformation phenomena in the study area, the validation of DEMs, the seismotectonic analysis of several important faults, the geodynamics of Central Macedonia as it is drawn from extensive GPS measurements and additional assessment of data and methods implemented.Η «Παρατήρηση της Γης» (Earth Observation) από το διάστημα αποτελεί σήμερα κεντρικό άξονα της Ευρωπαϊκής περιβαλλοντικής πολιτικής. Στο πλαίσιο αυτό, το γνωστικό αντικείμενο της Τηλεπισκόπησης και ιδιαίτερα η διαστημική του έκφανση γνωρίζει ιδιαίτερη ανάπτυξη. Η αλματώδης πρόοδος της διαστημικής τεχνολογίας, υπήρξε καθοριστική στην καθιέρωση της Τηλεπισκόπησης στο χώρο των Γεωεπιστημών. Παράλληλα, νέες τεχνικές και προηγμένες δυνατότητες ψηφιακής επεξεργασίας των τηλεπισκοπικών δεδομένων, σε συνδυασμό με πρόσθετα εργαλεία της σημερινής τεχνολογίας, όπως τα Συστήματα Γεωγραφικών Πληροφοριών (Geographical Information Systems/GIS) και τα Παγκόσμια Δορυφορικά Συστήματα Πλοήγησης (Global Navigation Satellite Systems/GNSS), έχουν θεμελιώσει άνευ προηγουμένου δυνατότητες συλλογής, σύνθεσης, ανάλυσης και αναπαράστασης εξαιρετικά ετερόκλητων δεδομένων και πληροφοριών, με εντυπωσιακά αποτελέσματα στην ψηφιακή αναπαράσταση του γήινου αναγλύφου και τη χαρτογράφηση διαφόρων γεωδυναμικών φαινομένων στην επιφάνεια της Γης. Το αντικείμενο, το οποίο πραγματεύεται η παρούσα διδακτορική διατριβή, είναι η συμβολή της διαστημικής/δορυφορικής Τηλεπισκόπησης στις Γεωεπιστήμες, με έμφαση: (1) στις δυνατότητες συνέργιας με τα Συστήματα Γεωγραφικών Πληροφοριών (Geographical Information Systems/GIS) και τα Παγκόσμια Δορυφορικά Συστήματα Πλοήγησης (Global Navigation Satellite Systems/GNSS), (2) στις τοπογραφικές-γεωδαιτικές δυνατότητες της Τηλεπισκόπησης με την εφαρμογή τεχνολογιών αιχμής όπως η συμβολομετρία SAR (SAR Interferometry/InSAR) και (3) στην αξιολόγηση των τηλεπισκοπικών τεχνικών και δεδομένων (εικόνες, ψηφιακά μοντέλα εδάφους, δεδομένα GPS) στις Γεωεπιστήμες. Το πεδίο εφαρμογής αφορά κυρίως τους κλάδους της Γεωμορφολογίας, Μορφοτεκτονικής και Σεισμοτεκτονικής. Ειδικότερα, σκοπός ήταν η ειδική επεξεργασία και ανάλυση δορυφορικών εικόνων διαφορετικής χωρικής και φασματικής ανάλυσης (ENVISAT/ASAR, ERS, TerraSAR-X, SPOT-5, LANDSAT) σε συνδυασμό με τη συλλογή και επεξεργασία άλλων δεδομένων (π.χ. εκτεταμένων κινηματικών δεδομένων GPS), καθώς και η χρήση και αξιολόγηση ψηφιακών μοντέλων εδάφους (Digital Elevation Models/DEMs) από διάφορες πηγές (SRTM, GDEM, InSAR κ.α.), στο χώρο της Κεντρικής Μακεδονίας. Το επίκεντρο του ενδιαφέροντος εντοπίζεται στην ευρύτερη περιοχή της Μυγδονίας Λεκάνης (μορφο-σεισμοτεκτονικού ενδιαφέροντος), στο οικιστικό συγκρότημα της Θεσσαλονίκης και τέλος στην ευρύτερη περιοχή του Καλοχωρίου, όπου απαντούν φαινόμενα καθίζησης. Τα αποτελέσματα της διατριβής αφορούν νέα στοιχεία που προέκυψαν για τα φαινόμενα καθίζησης και παραμόρφωσης γύρω από τη Θεσσαλονίκη, την αξιολόγηση της ακρίβειας των DEM, τη σεισμοτεκτονική ανάλυση σημαντικών ρηγμάτων της περιοχής μελέτης, το γεωδυναμικό καθεστώς στην Κεντρική Μακεδονία, όπως αυτό προκύπτει από μετρήσεις GPS, καθώς και τις επιμέρους αξιολογήσεις των χρησιμοποιούμενων δεδομένων και τεχνικών

Approaches for land cover monitoring over Europe based on backscatter and coherence properties of Envisat and ERS SAR data

The purpose of this study is the exploitation of Synthetic Aperture Radar (SAR) satellite data for land cover monitoring. The properties of the recorded radar data heavily depend on the type of land cover, season and weather conditions. Therefore, it is possible to utilize the variability of these factors, in order to develop various techniques and methodologies that can be used for classifying land surfaces. In this context, this paper proposes approaches, which include the application of mathematical expressions and application of thresholds on multi-temporal data, for recognizing and classifying various types of land cover, on the basis of ERS and Envisat C-band SAR backscatter and coherence properties. These can be useful for any kind of contemporary SAR data, such as those of the current two Sentinel-1 satellites. Although this study focuses on four main land cover types (urban, mountainous, agricultural-low vegetation and forested areas) over specific areas in Europe, the same principles can be extended worldwide, leading to useful insights for designing future SAR satellite missions or for establishing guidelines for in-depth studies of specific land cover types

European Digital Elevation Model Validation against Extensive Global Navigation Satellite Systems Data and Comparison with SRTM DEM and ASTER GDEM in Central Macedonia (Greece)

Digital elevation models (DEMs) are a widely used form of topographic information, with some of the most popular being the Shuttle Radar Topography Mission (SRTM) DEM and the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM). These two sources of topographical information are the main constituents of the European Union Digital Elevation Model (EU-DEM), which is a relatively new dataset of the EU’s Copernicus Land Monitoring Service. In this context, the purpose of this study was to validate EU-DEM for its vertical accuracy and to compare it with SRTM DEM and ASTER GDEM data. This was achieved in a Geographic Information System (GIS) environment, using extensive—in the order of tens of thousands of points—geodetic Global Navigation Satellite System (GNSS) measurements and appropriate pre-processing steps. The absolute elevation errors results had a Root Mean Square Error (RMSE) of 2.7 m at a 90% confidence level and characterize the performance of EU-DEM from local to regional scale, generally confirming that it is an enhanced source of elevation information when compared with its predecessors

Earth Observation Data Synergy for the Enhanced Monitoring of Ephemeral Water Bodies to Anticipate Karst-Related Flooding

With the increasing availability and diversity of satellite imagery, the multisensor fusion of data can more effectively address the improved monitoring of temporary water bodies. This study supports the attempt to apply well established methods to detect spatial and temporal changes in ephemeral shallow lakes in lowland karst terrain, as well as to improve the understanding concerning the dynamics of water storage and hydrological mechanisms during extreme precipitation events. Based on the joint analysis of Copernicus Sentinel SAR and optical mission data, as well as soil moisture and EO-based rainfall observations over the period of 2015–2020, we demonstrated the control of the karst system on the ephemeral lake appearances in the broader area of Chalkida (Evvia, Greece). A connection between the prolonged and extended water coverage in the ephemeral lakes and flooding in the area is documented. Our EO-supported findings may serve as indicators for flood alerts in future extreme precipitation events, improving responses in cases of emergencies

Advanced InSAR techniques for deformation studies and for simulating the PS-assisted calibration procedure of Sentinel-1 data: case study from Thessaloniki (Greece), based on the Envisat/ASAR archive

Using state-of-the-art InSAR techniques, namely persistent scatterers (PSs) and small baseline subset (SBAS) approaches, this study contributes to open geotechnical questions in the area of Thessaloniki (Greece) from a remote-sensing perspective. It also demonstrates the potential of these techniques for calibration purposes, with reference to the new C-band synthetic aperture radar (SAR) sensor on board the Sentinel-1 mission satellites. By exploiting the historical archive of Envisat/ASAR data, as well as a pair of the first Sentinel-1A SAR images, recent (2004-2010) deformation rates up to 18 mm year(-1) are detected over the study area. These results are then compared to the findings of previous InSAR and geophysical observations, indicating for example, subsidence or tectonic activity. On the other hand, the usefulness of the PS technique is shown over the same region for external SAR calibration purposes. This process simulates the PS-assisted calibration procedure to be applied systematically to Sentinel-1 SAR products

Educational Field Trips as Part of Teaching Methodology in Adult Education

In modern times, adult education is growing at a significant pace as many adults worldwide are actively involved in learning processes to update their knowledge and skills. In adult education, experiential learning plays a central role which renders learners active participants in the learning process. Educational field trips are part of experiential learning. Several scientific studies have been carried out in recent years that highlight the importance of educational field trips in a learning process, but most of them concern school education. This research focuses on the field of adult education, exploring the benefits as well as the conditions for successful visits in this field. By studying a sample of in-service learners and educators, the research demonstrates the importance of educational field trips as a useful tool for promoting experiential and participatory learning in adult education. Participants in this study highlight the main benefits of educational field trips and the preconditions that need to be met for their successful implementation

Land Cover-Specific Local Incidence Angle Correction: A Method for Time-Series Analysis of Forest Ecosystems

This study deals with a local incidence angle correction method, i.e., the land cover-specific local incidence angle correction (LC-SLIAC), based on the linear relationship between the backscatter values and the local incidence angle (LIA) for a given land cover type in the monitored area. Using the combination of CORINE Land Cover and Hansen et al.’s Global Forest Change databases, a wide range of different LIAs for a specific forest type can be generated for each scene. The algorithm was developed and tested in the cloud-based platform Google Earth Engine (GEE) using Sentinel-1 open access data, Shuttle Radar Topography Mission (SRTM) digital elevation model, and CORINE Land Cover and Hansen et al.’s Global Forest Change databases. The developed method was created primarily for time-series analyses of forests in mountainous areas. LC-SLIAC was tested in 16 study areas over several protected areas in Central Europe. The results after correction by LC-SLIAC showed a reduction of variance and range of backscatter values. Statistically significant reduction in variance (of more than 40%) was achieved in areas with LIA range >50° and LIA interquartile range (IQR) >12°, while in areas with low LIA range and LIA IQR, the decrease in variance was very low and statistically not significant. Six case studies with different LIA ranges were further analyzed in pre- and post-correction time series. Time-series after the correction showed a reduced fluctuation of backscatter values caused by different LIAs in each acquisition path. This reduction was statistically significant (with up to 95% reduction of variance) in areas with a difference in LIA greater than or equal to 27°. LC-SLIAC is freely available on GitHub and GEE, making the method accessible to the wide remote sensing community

Educational Field Trips as Part of Teaching Methodology in Adult Education

In modern times, adult education is growing at a significant pace as many adults worldwide are actively involved in learning processes to update their knowledge and skills. In adult education, experiential learning plays a central role which renders learners active participants in the learning process. Educational field trips are part of experiential learning. Several scientific studies have been carried out in recent years that highlight the importance of educational field trips in a learning process, but most of them concern school education. This research focuses on the field of adult education, exploring the benefits as well as the conditions for successful visits in this field. By studying a sample of in-service learners and educators, the research demonstrates the importance of educational field trips as a useful tool for promoting experiential and participatory learning in adult education. Participants in this study highlight the main benefits of educational field trips and the preconditions that need to be met for their successful implementation

Interactive Web Mapping Applications for 2D and 3D Geo-Visualization of Persistent Scatterer Interferometry SAR Data

Surface motion is a complex, dynamic phenomenon that draws significant scientific attention. This study focuses on the development of a cartographic toolset for the visualization of space-borne Persistent Scatterer Interferometry (PSI) surface motion measurements. The entire archive of Sentinel-1 Synthetic Aperture Radar (SAR) imagery over the broader Thessaloniki (Greece) area has been exploited to derive the PSI measurements utilizing the Surface motioN mAPPING (SNAPPING) service on the Geohazards Exploitation Platform (GEP). A collection of web map applications, interactive visualization tools, and an animated map were developed based on state-of-the-art approaches. This geo-visualization toolset consists of the following: (i) Three web map applications exploring PSI velocity rates, PSI time series, and a comparison of PSI with geodetic leveling data; (ii) Two interactive map tools focusing on 3D visualization of PSI time series and estimating velocity rates for predefined temporal frames; and (iii) An animated map of PSI time series. The utilization of the aforementioned visualization toolset provided useful conclusions about the variety of land displacement that occurs in different subareas of Northern Greece from different causes. More specifically, certain subareas with significant subsidence rates range from −2 mm/year up to −18 mm/year from 2015 to 2020. The magnitude of displacement and the underlying causes (subsidence, faults, landslides, human processes, etc.) varies across different subareas. On the other hand, a subarea of uplift trend exists in the north of the city of Thessaloniki with displacements up to 5 mm/year for the period between 2015–2020, despite being constrained by the fact that the geo-visualization platform is able to display SNAPPING PSI measurements from any location around the world, making it a useful tool for global exploration. The platform’s contents are available through a user-friendly graphical interface and are mostly addressed to domain experts as well as end-users. Opposed to similar approaches where static 2D maps and velocity rates web applications are presented through this platform, users can monitor and study the dynamic behavior of surface motion to a spatiotemporal extent more thoroughly