Oil Spill Detection and Mapping Using Sentinel 2 Imagery

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, Greece. The preliminary results are considered very successful and consistent, with a high degree of applicability to other Sentinel 2 satellite images. Further testing and fine tuning of the proposed object-based methodology should be carried out using atmospheric correction and ground truth

Oil Spill Detection and Mapping Using Sentinel 2 Imagery

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, Greece. The preliminary results are considered very successful and consistent, with a high degree of applicability to other Sentinel 2 satellite images. Further testing and fine tuning of the proposed object-based methodology should be carried out using atmospheric correction and ground truth

Development of an integrated system of hyperspectral and thermal remote sensing sensors for the detection of coastal and submarine springs

It is estimated that in Greece often karstic water flows via submarine and coastal springs into the sea causing enormous losses of this most precious natural resource. Thus, the exploitation of water that is lost in the sea is of critical importance, mainly for the islands of our country which face the most severe problems of water shortage but also for the continental regions in which the dramatic water shortage becomes more decisive. The research which led to the particular doctoral thesis deals with the development, application and evaluation of methods and techniques for the detection of coastal and submarine springs of water in coastal and island regions with exploitation of airborne thermal and hyperspectral remote sensing acquisition systems. In the framework of the relevant research, it was designed, documented and implemented the first in Greece airborne system for the acquisition of thermal and hyperspectral remote sensing imagery. The system is constituted by the thermal sensor TABI-320 and the hyperspectral sensor CASI-550, constructed by the Canadian company ITRES, as well as the INS/GPS unit CMIGITS III, constructed by BEI Technologies. Moreover, the most adequate methodology has been developed for the detection of coastal and/or submarine springs of natural/brackish water with the use of this system. Aerial acquisitions of thermal and hyperspectral remote sensing imagery have been carried out in parallel with oceanographic and in situ hyperspectral measurements in regions of known coastal and submarine springs near the city of Halkis. Cross-correlations of aerial imagery and in situ measurements were used for the development of the most suitable methodology for the detection of coastal and/or submarine springs based on the most optimal combined exploitation and integration of the thermal and hyperspectral imagery. The first phase of the research aimed at the complete comprehension and explanation of the way that the coastal or submarine springs affect the surrounding sea water and moreover, the way, the sizes and the qualities of their influences on the thermal and hyperspectral remote sensing imagery. Based on the analysis and processing that has been carried out, the methodology for the detection of coastal and submarine springs of natural/brackish water has been documented. The developed methodology encompasses: a) the appropriate planning of the thermal and hyperspectral image acquisition, b) the appropriate setup of the sensors for the remote sensing imagery acquisitions, and c) the detection of the coastal and submarine springs of natural/brackish water and thedetermination of their exact locations. The effectiveness of the developed methodology has been evaluated, verified and confirmed with the detection of new springs in the islands of Skopelos and Kythira. The determination of the exact locations of the coastal and submarine springs in a region, in combination with the relevant hydrogeological study for the region, may help in the determination of the more suitable places for pumping water, as well as the study and manufacture of essential works for its preservation and exploitation.Στη χώρα μας εκτιμάται ότι πολλοί καρστικοί υδροφόροι ορίζοντες εκφορτίζονται μέσωυποθαλασσίων και παρακτίων πηγών στη θάλασσα με αποτέλεσμα να έχουμε τρομακτικέςαπώλειες του πολυτιμότατου φυσικού πόρου του νερού. Έτσι, η αξιοποίηση του νερού που χάνεται στη θάλασσα αποκτά ιδιαίτερα κρίσιμη σημασία, κυρίως για τα νησιά της χώρας μας τα οποία αντιμετωπίζουν σημαντικότατα προβλήματα λειψυδρίας αλλά και γενικότερα για τις ηπειρωτικές περιοχές στις οποίες γίνεται όλο και πιο καθοριστική η δραματική μείωση των υδατικών διαθεσίμων. Η έρευνα η οποία οδήγησε στη συγκεκριμένη διδακτορική διατριβή πραγματεύεται την ανάπτυξη, εφαρμογή και αξιολόγηση μεθόδων και τεχνικών ανίχνευσης παρακτίων και υποθαλασσίων πηγών νερού σε παράκτιες και νησιωτικές περιοχές με αξιοποίηση αερομεταφερόμενων θερμικών και υπερφασματικών τηλεπισκοπικών δεκτών. Στο πλαίσιο της σχετικής έρευνας, σχεδιάστηκε, τεκμηριώθηκε και υλοποιήθηκε το πρώτο στην Ελλάδα αερομεταφερόμενο σύστημα λήψης θερμικών και υπερφασματικών τηλεπισκοπικών απεικονίσεων, το οποίο αποτελείται από τον θερμικό δέκτη TABI-320 και τον υπερφασματικό δέκτη CASI-550 της Καναδικής εταιρίας ITRES καθώς και μία αδρανειακή/GPS μονάδα CMIGITS III της εταιρίας BEI Technologies. Επιπλέον, αναπτύχθηκε η πλέον ενδεικνυόμενη μεθοδολογία για την ανίχνευση παρακτίων ή/και υποθαλασσίων πηγών γλυκού/υφάλμυρου νερού με χρήση του συστήματος αυτού. Πραγματοποιήθηκαν εναέριες λήψεις θερμικών και υπερφασματικών τηλεπισκοπικών απεικονίσεων παράλληλα με ωκεανογραφικές και επίγειες υπερφασματικές μετρήσεις σε περιοχές άγνωστών παρακτίων και υποθαλασσίων πηγών κοντά στην πόλη της Χαλκίδας. Οι συσχετίσεις εναερίων και επιγείων καταγραφών χρησιμοποιήθηκαν για την ανάπτυξη της καταλληλότερης μεθοδολογίας ανίχνευσης των παρακτίων ή/και υποθαλασσίων πηγών με βάση τη βέλτιστη συνδυαστική αξιοποίηση και ολοκλήρωση των δυνατοτήτων των θερμικών και των υπερφασματικών τηλεπισκοπικών απεικονίσεων. Κατά την πρώτη φάση της έρευνας, επιδιώχθηκε η πλήρης κατανόηση και εξήγηση του τρόπου με τον οποίο επιδρούν οι παράκτιες ή υποθαλάσσιες πηγές στο περιβάλλον θαλασσινό νερό και επιπλέον, ο τρόπος, τα μεγέθη και οι ποιότητες της καταγραφής της επίδρασης αυτής στις θερμικές και στις υπερφασματικές τηλεπισκοπικές απεικονίσεις. Με βάση τις αναλύσεις και τις επεξεργασίες οι οποίες πραγματοποιήθηκαν τεκμηριώθηκε στησυνέχεια η μεθοδολογία ανίχνευσης των παρακτίων και υποθαλασσίων πηγών γλυκού/υφάλμυρου νερού η οποία αφορά: α) στο σωστό προγραμματισμό των λήψεων των θερμικών και υπερφασματικών τηλεπισκοπικών απεικονίσεων, β) στις ρυθμίσεις των δεκτών για την πραγματοποίηση των λήψεων, και γ) στον τρόπο ανίχνευσης των πιθανών παρακτίων και υποθαλασσίων πηγών γλυκού/υφάλμυρου νερού και τον προσδιορισμό της ακριβούς θέσης τους. Η αποτελεσματικότητα της μεθοδολογίας η οποία αναπτύχθηκε αξιολογήθηκε και επιβεβαιώθηκε με την ανίχνευση νέων πηγών στα νησιά της Σκοπέλου και των Κυθήρων. Ο προσδιορισμός της ακριβούς θέσης των υποθαλασσίων και παρακτίων πηγών νερού σε μια περιοχή, σε συνδυασμό με την υδρογεωλογική μελέτη της περιοχής, είναι δυνατό να βοηθήσουν στον καθορισμό των καταλληλότερων σημείων άντλησης του νερού, αλλά και μελέτης και κατασκευής των απαραίτητων έργων συγκράτησης και αξιοποίησής του

Mapping of forest tree distribution and estimation of forest biodiversity using Sentinel-2 imagery in the University Research Forest Taxiarchis in Chalkidiki, Greece

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 Greece. The research is based on OBIA being developed on to bi-temporal summer and winter Sentinel-2 imagery. Fuzzy rules, which are based on topographic factors, such as terrain elevation and slope for the distribution of each tree species, derived from expert knowledge and field observations, were used to improve the accuracy of tree species classification. Finally, Simpson’s diversity index for forest tree species, was calculated and mapped, constituting a relative indicator for biodiversity for forest ecosystem organisms (fungi, insects, birds, reptiles, mammals) and carrying implications for the identification of patches prone to disturbance or that should be prioritized for conservation

Time Series Analysis of Landsat Data for Investigating the Relationship between Land Surface Temperature and Forest Changes in Paphos Forest, Cyprus

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 LST values and create a time series. Using the Cook’s distance, the effect of missing values in the analysis of the time series were examined. Results from the cross‐correlation and cross‐variograms, decomposition model, and the BFAST algorithm were compared to produce reliable conclusions on forest changes and satellite, meteorological, and environmental data were combined to interpret the changes that occurred inside the forest. The decomposition analysis showed a decrease of 2.7% in the LST for the period 1993–2000 and an increase of 4.6% in the LST during the period 2013–2018. The NDVI trend is negatively correlated to the LST trend for both time periods. An increase in the LST trend was identified in November 1998 as well as in the NDVI trend in October 1994 and May 2014 that was caused by favorable climatic conditions. An increase in the NDVI trend from May 2014 to December 2015 may be related to reduced pityocampa attacks. An abrupt decrease was detected in December 2015 that was probably caused by the locust invasion that occurred in the island earlier that year. A positive correlation appears for LST and NDVI variables for time lags 4, 5, 6, 7, and 8 months. Overall, it was shown that LST and NDVI analysis is very promising for identifying potential forest decline

Time Series Analysis of Landsat Data for Investigating the Relationship between Land Surface Temperature and Forest Changes in Paphos Forest, Cyprus

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 LST values and create a time series. Using the Cook’s distance, the effect of missing values in the analysis of the time series were examined. Results from the cross-correlation and cross-variograms, decomposition model, and the BFAST algorithm were compared to produce reliable conclusions on forest changes and satellite, meteorological, and environmental data were combined to interpret the changes that occurred inside the forest. The decomposition analysis showed a decrease of 2.7% in the LST for the period 1993–2000 and an increase of 4.6% in the LST during the period 2013–2018. The NDVI trend is negatively correlated to the LST trend for both time periods. An increase in the LST trend was identified in November 1998 as well as in the NDVI trend in October 1994 and May 2014 that was caused by favorable climatic conditions. An increase in the NDVI trend from May 2014 to December 2015 may be related to reduced pityocampa attacks. An abrupt decrease was detected in December 2015 that was probably caused by the locust invasion that occurred in the island earlier that year. A positive correlation appears for LST and NDVI variables for time lags 4, 5, 6, 7, and 8 months. Overall, it was shown that LST and NDVI analysis is very promising for identifying potential forest decline

A Selection of Experiments for Understanding the Strengths of Time Series SAR Data Analysis for Finding the Drivers Causing Phenological Changes in Paphos Forest, Cyprus

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 of synthetic aperture radar (SAR) data, but it is still unknown how these data could be utilised for better understanding forest phenology and climate-related alternations. This study investigates the phenological cycle of Paphos forest, Cyprus using SAR data from 1992 to 2021, acquired by ERS-1/2, Envisat and Sentinel-1. An average phenological diagram was created for each space mission and a more detailed analysis was performed from October 2014 to November 2021, using the higher temporal resolution of Sentinel-1 data. Meteorological data were used to better understand the drivers of blooming alternations. Using the interquartile range (IQR), outliers were detected and replaced using the Kalman filter imputation. Forecasting trend lines were used to estimate the amplitude of the summer peaks and the annual mean. The observation of the average phenology from each satellite mission showed that there were two main blooming peaks each year: the winter and the summer peak. We argue that the winter peak relates to increased foliage, water content and/or increased soil moisture. The winter peak was followed by a fall in February reaching the lower point around March, due to the act of pine processionary (Thaumetopoea pityocampa). The summer peak should relate to the annual regeneration of needles and the drop of the old ones. A delay in the summer peak—in August 2018—was associated with increased high temperatures in May 2018. Simultaneously, the appearance of one peak instead of two in the (Formula presented.) time series during the period November 2014–October 2015 may be linked to a reduced act of the pine processionary associated with low November temperatures. Furthermore, there was an outlier in February 2016 with very low backscattering coefficients and it was associated with a drought year. Finally, predicting the amplitude of July 2020 returned high relevant Root Mean Square Error (rRMSE). Seven years of time series data are limiting for predicting using trend lines and many parameters need to be taken into consideration, including the increased rainfall between November 2018 and March 2020

Airborne Spectral Reflectance Dataset of Submerged Plastic Targets in a Coastal Environment

Among the emerging applications of remote sensing technologies, the remote detection of plastic litter has observed successful applications in recent years. However, while the number of studies and datasets for spectral characterization of plastic is growing, few studies address plastic litter while being submerged in natural seawater in an outdoor context. This study aims to investigate the feasibility of hyperspectral characterization of submerged plastic litter in less-than-ideal conditions. We present a hyperspectral dataset of eight different polymers in field conditions, taken by an unmanned aerial vehicle (UAV) on different days in a three-week period. The measurements were carried out off the coast of Mytilene, Greece. The team collected the dataset using a Bayspec OCI-F push broom sensor from 25 m and 40 m height above the water. For a contextual background, the dataset also contains optical (RGB) high-resolution orthomosaics

Detection of marine fronts: a comparison between different approaches applied on the SST product derived from Sentinel-3 data

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 that reason, this study tests how two different edge detection methodologies (Laplacian and Canny) performs on detecting marine once applied on the Sea Surface Temperature (SST) product of the Sentinel-3 SLSTR instrument. In a few words, the results of this study showed that the Laplacian edge detection overestimates fronts, while the Canny Edge detection algorithm underestimates them. It worth highlighting though that the results are significantly improved using the appropriate filtering and/or image enhancements. The results of the Canny Edge detection algorithm were improved when a histogram equalisation image enhancement was applied before the Canny Edge and the results of the Laplacian detector were improved with median filtering