In this paper textural parameters resulted from grey level co-occurrence matrices (GLCMs), first ... more In this paper textural parameters resulted from grey level co-occurrence matrices (GLCMs), first order statistics and Fourier power spectrum techniques are used to develop an adaptive and simple to use, texel based classification method for sidescan sonar imagery. Sonar imagery contains textures with no distinct acoustic signatures that moreover vary in space due to many reasons. In addition, GLCM statistics, that are the most capable among the texture analysis techniques, require several parameters to be set a priori as inputs (offset, no of directions, window sizing e.t.c.). The above mentioned facts turn feature calibration and selection processes into issues of great complicity and importance towards the development of a valid classification system. In the present study a methodological scheme according to which variables to be used for classification are chosen between the others through an automated process, is suggested. Throughout this process all possible combinations betwe...
Hydrodynamic numerical models nowadays offer great aid when studying the physical behavior of coa... more Hydrodynamic numerical models nowadays offer great aid when studying the physical behavior of coastal waters. However, the calibration and furthermore the verification of such models, is a difficult process that should be applied carefully, especially when little direct hydrodynamic data has been collected from the study area. This paper suggests a methodology for indirect verification of mathematical coastal circulation models, by means of image processing and interpretation of Landsat's TM reflective bands 3 and 6 imagery. This approach is an efficient practice and is easily available even though no field survey was carried out. This method was successfully applied to Saronikos Gulf and in particular to gulf of Megara, located westwards of Salamis Island, where the dispersion of a plume formed by urban waste waters was examined. The satellite data processing derivatives were found to be in accordance with the results of the circulation simulation and thus the parameters used for the calibration of the model can be considered successfully selected.
Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employin... more Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employing an integrated approach, data from both beach and underwater sites were analyzed. The average litter density on beaches was 2.61 items m − 2 , with plastic being the most common material, notably small polystyrene fragments and cigarette butts. The western part of the Gulf exhibited higher litter density, mainly due to surface circulation patterns. Most beaches fell short of meeting Good Environmental Status criteria for marine litter. Higher litter densities were observed in autumn. Benthic litter density decreased with depth, being 23 times higher in shallower waters, with plastic being the predominant type. This extensive study offers crucial insights into the pollution status and litter distribution in the Saronikos Gulf, contributing significantly to the global understanding of marine litter distribution on coastal ecosystems. Such information is crucial for raising awareness, informing policy decisions, and driving environmental actions.
Global NEST International Conference on Environmental Science & Technology
In the port of Thessaloniki, Greece, benthic megalitter detection was achieved using an Unmanned ... more In the port of Thessaloniki, Greece, benthic megalitter detection was achieved using an Unmanned Surface Vehicle (USV) equipped with a compact high resolution sidescan sonar (SSS) and a single beam echsosounder (SBES). The benthic megalitter survey was organized in two separate phases. Firstly, a systematic hydroacoustic survey using the SBES and SSS managed to outline and map all the acoustic anomalies. The second phase followed using the ROV hovered over these acoustic anomalies and the sites were identified on the video camera. An Automated Target Detection procedure, based on acoustic texture analysis and Independent Component Analysis (ICA), was applied for the automated detection of acoustic anomalies. The ground truth survey attested that the anomalies represent megalitter (metallic items, car tires, wires, e.t.c.). The developed procedure had promising results towards fast detection of the benthic megalitter in coastal areas.
Global NEST International Conference on Environmental Science & Technology
The marine environment is the final recipient and digester of litter. Floating and benthic litter... more The marine environment is the final recipient and digester of litter. Floating and benthic litter constitute the majority of litter items in the marine environment while both remain quite unexploited due to their demand in high-cost and time-consuming surveys. In this paper we propose an integrated approach for assessing in detail the spatial distribution and composition of benthic litter in coastal environments, through the use of underwater towed cameras. The method is showcased in Syros Island, Cyclades, Greece where benthic litter density maps revealed benthic litter sources and environmental drivers controlling their spatial distribution and general pathways.
Bulletin of the Geological Society of Greece, 2007
Οι πeριβαλλοντικές βάσeις δeδομένων συχνά αντιμeτωπίζουν τα προβλήματα της άτακτης δeιγματοληψίας... more Οι πeριβαλλοντικές βάσeις δeδομένων συχνά αντιμeτωπίζουν τα προβλήματα της άτακτης δeιγματοληψίας στον χρόνο και της έλλeιψης μeτρήσeων για κάποιeς πeριόδους. Το γeγονός αυτό eμποδίζeι τη χρήση των κλασικών μeθόδων ανάλυσης χρονοσeιρών, οι οποίeς απαιτούν σταθeρό χρονικό βήμα eνώ ταυτόχρονα τα χρονικά κeνά eισάγουν δυσκολίeς στην χρήση των πeρισσοτέρων μeθόδων πολυδιάστατης σταπστικής ανάλυσης. Η παρούσα eργασία προτeίνeι ένα πλήρeς μeθοδολογικό σχήμα ανάλυσης χρονικών πeριβαλλονπκών δeδομένων μe δeιγματοληπτική ανομοιογένeια, στο οποίο γίνeται χρήση του αλγορίθμου CLEAN και της Παραγοντικής ανάλυσης (Factor Analysis). Ο αλγόριθμος CLEAN έχeι την ικανότητα να αναπλάθeι τις αρχικές χρονοσeιρές της βάσης δeδομένων χρησιμοποιώντας φασματική ανάλυση και να δημιουργeί καινούργιeς μe σταθeρό χρονικό βήμα και έλλeιψη κeνών. Λαμβάνeι χώρα δηλαδή τόσο συμπλήρωση των κeνών τ?/ς βάσης, όσο και «eξυγίανση» της δeιγματοληψίας της. Η παραγοντική ανάλυση ομαδοποιeί τις μeταβλητές, ανάλογα μe τον π...
The documentation of underwater cultural heritage (UCH) is the basis for sustainable maritime dev... more The documentation of underwater cultural heritage (UCH) is the basis for sustainable maritime development including its protection, preservation, and incorporation in coastal zone management plans. In this study, we present a multidisciplinary, non-intrusive downscale approach for the documentation of UCH implemented on the coastal area of Aegina Island, Greece, where a unique submerged harbour complex is preserved. This approach succeeded in obtaining information that serves both geomorphological and archaeological purposes in a time- and cost-effective way, while obtaining information of centimeters to millimeters scale. The geomorphology of the area was mapped in detail through marine geophysical means while ancient submerged conical rubble structures and breakwaters were documented using automatic seafloor segmentation techniques, revealing previously unknown sites of archaeological interest. The structures’ parameters were extracted from the acoustic data to analyze their morph...
The distribution of the natural radionuclides (238 U, 232 Th, 226 Ra, 40 K) and the artificial 13... more The distribution of the natural radionuclides (238 U, 232 Th, 226 Ra, 40 K) and the artificial 137 Cs was studied in sediment cores collected from Amvrakikos Gulf, a seasonal anoxic marine basin, using gray spectrometry. The activity of radionuclides, along with the concentrations of Fe and Mn, were also studied in relation to the total organic carbon and the granulometric fractions of the sediments. The results obtained revealed higher 238 U activity concentrations in all the examined sediment samples compared to the world and Greek average values for soil. The high activity values of 238 U are attributed, besides the lattice-held fraction, to phosphate fertilizer inputs in the Gulf via major rivers and/or to alteration processes of phosphate ores located mainly in the drainage basin of the river Louros. The elevated activity values of 40 K could be attributed to the mineralogical composition of the sediments and to phosphate fertilizers containing potassium. Organic matter seems to be a more efficient sorbent for U than clay minerals and amorphous Fe and Mn-oxyhydroxides. Scanning electron microscopy, together with qualitative analysis of some smectites, reveals the occurrence of U, suggesting a limited absorption of U onto clay minerals. The applied BCR sequential extraction procedure revealed that U was found mainly in the refractory phase or associated with organic matter and to a lesser extent as surface-coating oxides, with the exception of one sediment core which is characterized by high content of fresh marine organic matter and presents high percentage of U in the exchangeable fraction.
Abstract Posidonia oceanica, a key seagrass spe-cies of the Mediterranean Sea, shows clear signs ... more Abstract Posidonia oceanica, a key seagrass spe-cies of the Mediterranean Sea, shows clear signs of regression throughout the Mediterranean and illegal trawling is recognized as one of the main causes. We examined the condition of a P. oceanica meadow in Alykes Bay ( ...
Seafloor segmentation and characterization based on local textural properties of acoustic backsca... more Seafloor segmentation and characterization based on local textural properties of acoustic backscatter has been a subject of extensive research since 1980s due to highly textured appearance of sonar images. The approach consists of subdivision of sonar image in a set of patches of certain size and calculation for each patch a set of features reflecting the patch texture. Patch size is chosen as a trade-off between locality of a point being characterized and accuracy in feature calculation. At first these techniques have been applied to backscatter from sidescan sonars which lacked accurate geo-referencing and had qualitative character. Later, with advance of multibeam echosounders (MBES) it became possible to spatially locate every individual. This allowed application of texture-based techniques to real geographical space, so that predicted boundaries between different acoustic facies became experimentally verifiable. However, acoustic return from uncalibrated MBES influenced by a va...
Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employin... more Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employing an integrated approach, data from both beach and underwater sites were analyzed. The average litter density on beaches was 2.61 items m − 2 , with plastic being the most common material, notably small polystyrene fragments and cigarette butts. The western part of the Gulf exhibited higher litter density, mainly due to surface circulation patterns. Most beaches fell short of meeting Good Environmental Status criteria for marine litter. Higher litter densities were observed in autumn. Benthic litter density decreased with depth, being 23 times higher in shallower waters, with plastic being the predominant type. This extensive study offers crucial insights into the pollution status and litter distribution in the Saronikos Gulf, contributing significantly to the global understanding of marine litter distribution on coastal ecosystems. Such information is crucial for raising awareness, informing policy decisions, and driving environmental actions.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ABSTRACT Litter that accumulates in the marine environment is recognized as a global environmenta... more ABSTRACT Litter that accumulates in the marine environment is recognized as a global environmental problem with numerous adverse effects. Despite Greece having more than 16,000 km of coastline, studies on litter composition and sources on its beaches are scarce and fragmentary. Therefore, this study aimed to quantify beach-stranded litter by type of material (plastic, glass, paper, aluminum, other metals, building materials, rope) on 80 Greek beaches, and to explore the relationships between different litter materials and marine- and land-based sources. Field work and data collection were accomplished with the participation of 10,938 and 15,748 volunteers in 2006 and 2007, respectively, and were integrated in the nationwide campaign of voluntary beach clean-ups: “Clean up the Med.” The participation of thousands of volunteers of different ages and social backgrounds in the data collection process not only led to the realization of a national level survey, but also played a significant role in raising public awareness on marine environmental issues, and in promoting a sense of responsibility in protecting marine resources. Plastic was the most abundant litter material found on the surveyed beaches (43–51%), followed by paper (13–18%) and aluminum (7–12%). Onshore and nearshore recreational activities, such as bathing and recreational boating, appeared to be the most dominant litter sources, as they affect the majority (56) of the surveyed beaches, suggesting that environmental education and awareness could reduce the beach-litter pollution problem. Navigation seemed to be the dominant source of marine-based litter, affecting more than half (46) of the surveyed beaches.
Modern underwater remote sensing technology introduces many advantages that extend the range of c... more Modern underwater remote sensing technology introduces many advantages that extend the range of conventional diving work providing the means to survey in a detailed and systematic fashion large seafloor area. There are two general approaches regarding the application of these techniques in underwater archaeology; they are being increasingly used to identify, locate and map (i) ancient and historical shipwrecks lying on the seafloor or partly buried in it and (ii) the coastal palaeogeogra-phy and thus submerged sites of archaeological interest (submerged ancient cities, settlements, ports and man-made structures). The underwater remote sensing techniques most commonly applied to underwater archaeology employ: (i) single and multi-beam echosounders (ii) side scan sonar (acousting imaging), (iii) laser line scan (optical imaging) (iv) subbottom profiler, (v) marine magne-tometer and (vi) undersea vehicles. The objectives of this paper are twofold: (i) to present the results of remote s...
Advances in the Research of Aquatic Environment, 2011
ABSTRACT In the present paper a spectral time series reconstruction approach is demonstrated rega... more ABSTRACT In the present paper a spectral time series reconstruction approach is demonstrated regarding its suitability for treating missing values in long term, daily sampled rainfall time series. The core of the proposed model consists of the CLEAN algorithm, which reconstructs time series after modifying their frequency spectrum to exclude artifacts originated by nonstationarity and missing values. Further filtering and normalization of the predicted values in places where periods of missing observations occur enhance the model’s potentialities. For the validation of the model, eight daily sampled rainfall time series from rain stations located in the Louros basin, NW Greece, were used. Its ability to predict rainfall height for long periods (e.g. a month) of continuous missing observations is tested by introducing several artificial blanks of a month’s duration each in the time series and analyzing the success of the model in order to correctly predict them. The model’s accuracy indicator is built on the basis of a cross correlation function so that time lags of just a few days between observed and predicted values do not affect it. The model performed adequately, especially for the wet months where its accuracy reached levels greater than 75% implying that daily variability in rainfall height can be to some extent described in the frequency domain.
In this paper textural parameters resulted from grey level co-occurrence matrices (GLCMs), first ... more In this paper textural parameters resulted from grey level co-occurrence matrices (GLCMs), first order statistics and Fourier power spectrum techniques are used to develop an adaptive and simple to use, texel based classification method for sidescan sonar imagery. Sonar imagery contains textures with no distinct acoustic signatures that moreover vary in space due to many reasons. In addition, GLCM statistics, that are the most capable among the texture analysis techniques, require several parameters to be set a priori as inputs (offset, no of directions, window sizing e.t.c.). The above mentioned facts turn feature calibration and selection processes into issues of great complicity and importance towards the development of a valid classification system. In the present study a methodological scheme according to which variables to be used for classification are chosen between the others through an automated process, is suggested. Throughout this process all possible combinations betwe...
Hydrodynamic numerical models nowadays offer great aid when studying the physical behavior of coa... more Hydrodynamic numerical models nowadays offer great aid when studying the physical behavior of coastal waters. However, the calibration and furthermore the verification of such models, is a difficult process that should be applied carefully, especially when little direct hydrodynamic data has been collected from the study area. This paper suggests a methodology for indirect verification of mathematical coastal circulation models, by means of image processing and interpretation of Landsat's TM reflective bands 3 and 6 imagery. This approach is an efficient practice and is easily available even though no field survey was carried out. This method was successfully applied to Saronikos Gulf and in particular to gulf of Megara, located westwards of Salamis Island, where the dispersion of a plume formed by urban waste waters was examined. The satellite data processing derivatives were found to be in accordance with the results of the circulation simulation and thus the parameters used for the calibration of the model can be considered successfully selected.
Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employin... more Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employing an integrated approach, data from both beach and underwater sites were analyzed. The average litter density on beaches was 2.61 items m − 2 , with plastic being the most common material, notably small polystyrene fragments and cigarette butts. The western part of the Gulf exhibited higher litter density, mainly due to surface circulation patterns. Most beaches fell short of meeting Good Environmental Status criteria for marine litter. Higher litter densities were observed in autumn. Benthic litter density decreased with depth, being 23 times higher in shallower waters, with plastic being the predominant type. This extensive study offers crucial insights into the pollution status and litter distribution in the Saronikos Gulf, contributing significantly to the global understanding of marine litter distribution on coastal ecosystems. Such information is crucial for raising awareness, informing policy decisions, and driving environmental actions.
Global NEST International Conference on Environmental Science & Technology
In the port of Thessaloniki, Greece, benthic megalitter detection was achieved using an Unmanned ... more In the port of Thessaloniki, Greece, benthic megalitter detection was achieved using an Unmanned Surface Vehicle (USV) equipped with a compact high resolution sidescan sonar (SSS) and a single beam echsosounder (SBES). The benthic megalitter survey was organized in two separate phases. Firstly, a systematic hydroacoustic survey using the SBES and SSS managed to outline and map all the acoustic anomalies. The second phase followed using the ROV hovered over these acoustic anomalies and the sites were identified on the video camera. An Automated Target Detection procedure, based on acoustic texture analysis and Independent Component Analysis (ICA), was applied for the automated detection of acoustic anomalies. The ground truth survey attested that the anomalies represent megalitter (metallic items, car tires, wires, e.t.c.). The developed procedure had promising results towards fast detection of the benthic megalitter in coastal areas.
Global NEST International Conference on Environmental Science & Technology
The marine environment is the final recipient and digester of litter. Floating and benthic litter... more The marine environment is the final recipient and digester of litter. Floating and benthic litter constitute the majority of litter items in the marine environment while both remain quite unexploited due to their demand in high-cost and time-consuming surveys. In this paper we propose an integrated approach for assessing in detail the spatial distribution and composition of benthic litter in coastal environments, through the use of underwater towed cameras. The method is showcased in Syros Island, Cyclades, Greece where benthic litter density maps revealed benthic litter sources and environmental drivers controlling their spatial distribution and general pathways.
Bulletin of the Geological Society of Greece, 2007
Οι πeριβαλλοντικές βάσeις δeδομένων συχνά αντιμeτωπίζουν τα προβλήματα της άτακτης δeιγματοληψίας... more Οι πeριβαλλοντικές βάσeις δeδομένων συχνά αντιμeτωπίζουν τα προβλήματα της άτακτης δeιγματοληψίας στον χρόνο και της έλλeιψης μeτρήσeων για κάποιeς πeριόδους. Το γeγονός αυτό eμποδίζeι τη χρήση των κλασικών μeθόδων ανάλυσης χρονοσeιρών, οι οποίeς απαιτούν σταθeρό χρονικό βήμα eνώ ταυτόχρονα τα χρονικά κeνά eισάγουν δυσκολίeς στην χρήση των πeρισσοτέρων μeθόδων πολυδιάστατης σταπστικής ανάλυσης. Η παρούσα eργασία προτeίνeι ένα πλήρeς μeθοδολογικό σχήμα ανάλυσης χρονικών πeριβαλλονπκών δeδομένων μe δeιγματοληπτική ανομοιογένeια, στο οποίο γίνeται χρήση του αλγορίθμου CLEAN και της Παραγοντικής ανάλυσης (Factor Analysis). Ο αλγόριθμος CLEAN έχeι την ικανότητα να αναπλάθeι τις αρχικές χρονοσeιρές της βάσης δeδομένων χρησιμοποιώντας φασματική ανάλυση και να δημιουργeί καινούργιeς μe σταθeρό χρονικό βήμα και έλλeιψη κeνών. Λαμβάνeι χώρα δηλαδή τόσο συμπλήρωση των κeνών τ?/ς βάσης, όσο και «eξυγίανση» της δeιγματοληψίας της. Η παραγοντική ανάλυση ομαδοποιeί τις μeταβλητές, ανάλογα μe τον π...
The documentation of underwater cultural heritage (UCH) is the basis for sustainable maritime dev... more The documentation of underwater cultural heritage (UCH) is the basis for sustainable maritime development including its protection, preservation, and incorporation in coastal zone management plans. In this study, we present a multidisciplinary, non-intrusive downscale approach for the documentation of UCH implemented on the coastal area of Aegina Island, Greece, where a unique submerged harbour complex is preserved. This approach succeeded in obtaining information that serves both geomorphological and archaeological purposes in a time- and cost-effective way, while obtaining information of centimeters to millimeters scale. The geomorphology of the area was mapped in detail through marine geophysical means while ancient submerged conical rubble structures and breakwaters were documented using automatic seafloor segmentation techniques, revealing previously unknown sites of archaeological interest. The structures’ parameters were extracted from the acoustic data to analyze their morph...
The distribution of the natural radionuclides (238 U, 232 Th, 226 Ra, 40 K) and the artificial 13... more The distribution of the natural radionuclides (238 U, 232 Th, 226 Ra, 40 K) and the artificial 137 Cs was studied in sediment cores collected from Amvrakikos Gulf, a seasonal anoxic marine basin, using gray spectrometry. The activity of radionuclides, along with the concentrations of Fe and Mn, were also studied in relation to the total organic carbon and the granulometric fractions of the sediments. The results obtained revealed higher 238 U activity concentrations in all the examined sediment samples compared to the world and Greek average values for soil. The high activity values of 238 U are attributed, besides the lattice-held fraction, to phosphate fertilizer inputs in the Gulf via major rivers and/or to alteration processes of phosphate ores located mainly in the drainage basin of the river Louros. The elevated activity values of 40 K could be attributed to the mineralogical composition of the sediments and to phosphate fertilizers containing potassium. Organic matter seems to be a more efficient sorbent for U than clay minerals and amorphous Fe and Mn-oxyhydroxides. Scanning electron microscopy, together with qualitative analysis of some smectites, reveals the occurrence of U, suggesting a limited absorption of U onto clay minerals. The applied BCR sequential extraction procedure revealed that U was found mainly in the refractory phase or associated with organic matter and to a lesser extent as surface-coating oxides, with the exception of one sediment core which is characterized by high content of fresh marine organic matter and presents high percentage of U in the exchangeable fraction.
Abstract Posidonia oceanica, a key seagrass spe-cies of the Mediterranean Sea, shows clear signs ... more Abstract Posidonia oceanica, a key seagrass spe-cies of the Mediterranean Sea, shows clear signs of regression throughout the Mediterranean and illegal trawling is recognized as one of the main causes. We examined the condition of a P. oceanica meadow in Alykes Bay ( ...
Seafloor segmentation and characterization based on local textural properties of acoustic backsca... more Seafloor segmentation and characterization based on local textural properties of acoustic backscatter has been a subject of extensive research since 1980s due to highly textured appearance of sonar images. The approach consists of subdivision of sonar image in a set of patches of certain size and calculation for each patch a set of features reflecting the patch texture. Patch size is chosen as a trade-off between locality of a point being characterized and accuracy in feature calculation. At first these techniques have been applied to backscatter from sidescan sonars which lacked accurate geo-referencing and had qualitative character. Later, with advance of multibeam echosounders (MBES) it became possible to spatially locate every individual. This allowed application of texture-based techniques to real geographical space, so that predicted boundaries between different acoustic facies became experimentally verifiable. However, acoustic return from uncalibrated MBES influenced by a va...
Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employin... more Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employing an integrated approach, data from both beach and underwater sites were analyzed. The average litter density on beaches was 2.61 items m − 2 , with plastic being the most common material, notably small polystyrene fragments and cigarette butts. The western part of the Gulf exhibited higher litter density, mainly due to surface circulation patterns. Most beaches fell short of meeting Good Environmental Status criteria for marine litter. Higher litter densities were observed in autumn. Benthic litter density decreased with depth, being 23 times higher in shallower waters, with plastic being the predominant type. This extensive study offers crucial insights into the pollution status and litter distribution in the Saronikos Gulf, contributing significantly to the global understanding of marine litter distribution on coastal ecosystems. Such information is crucial for raising awareness, informing policy decisions, and driving environmental actions.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ABSTRACT Litter that accumulates in the marine environment is recognized as a global environmenta... more ABSTRACT Litter that accumulates in the marine environment is recognized as a global environmental problem with numerous adverse effects. Despite Greece having more than 16,000 km of coastline, studies on litter composition and sources on its beaches are scarce and fragmentary. Therefore, this study aimed to quantify beach-stranded litter by type of material (plastic, glass, paper, aluminum, other metals, building materials, rope) on 80 Greek beaches, and to explore the relationships between different litter materials and marine- and land-based sources. Field work and data collection were accomplished with the participation of 10,938 and 15,748 volunteers in 2006 and 2007, respectively, and were integrated in the nationwide campaign of voluntary beach clean-ups: “Clean up the Med.” The participation of thousands of volunteers of different ages and social backgrounds in the data collection process not only led to the realization of a national level survey, but also played a significant role in raising public awareness on marine environmental issues, and in promoting a sense of responsibility in protecting marine resources. Plastic was the most abundant litter material found on the surveyed beaches (43–51%), followed by paper (13–18%) and aluminum (7–12%). Onshore and nearshore recreational activities, such as bathing and recreational boating, appeared to be the most dominant litter sources, as they affect the majority (56) of the surveyed beaches, suggesting that environmental education and awareness could reduce the beach-litter pollution problem. Navigation seemed to be the dominant source of marine-based litter, affecting more than half (46) of the surveyed beaches.
Modern underwater remote sensing technology introduces many advantages that extend the range of c... more Modern underwater remote sensing technology introduces many advantages that extend the range of conventional diving work providing the means to survey in a detailed and systematic fashion large seafloor area. There are two general approaches regarding the application of these techniques in underwater archaeology; they are being increasingly used to identify, locate and map (i) ancient and historical shipwrecks lying on the seafloor or partly buried in it and (ii) the coastal palaeogeogra-phy and thus submerged sites of archaeological interest (submerged ancient cities, settlements, ports and man-made structures). The underwater remote sensing techniques most commonly applied to underwater archaeology employ: (i) single and multi-beam echosounders (ii) side scan sonar (acousting imaging), (iii) laser line scan (optical imaging) (iv) subbottom profiler, (v) marine magne-tometer and (vi) undersea vehicles. The objectives of this paper are twofold: (i) to present the results of remote s...
Advances in the Research of Aquatic Environment, 2011
ABSTRACT In the present paper a spectral time series reconstruction approach is demonstrated rega... more ABSTRACT In the present paper a spectral time series reconstruction approach is demonstrated regarding its suitability for treating missing values in long term, daily sampled rainfall time series. The core of the proposed model consists of the CLEAN algorithm, which reconstructs time series after modifying their frequency spectrum to exclude artifacts originated by nonstationarity and missing values. Further filtering and normalization of the predicted values in places where periods of missing observations occur enhance the model’s potentialities. For the validation of the model, eight daily sampled rainfall time series from rain stations located in the Louros basin, NW Greece, were used. Its ability to predict rainfall height for long periods (e.g. a month) of continuous missing observations is tested by introducing several artificial blanks of a month’s duration each in the time series and analyzing the success of the model in order to correctly predict them. The model’s accuracy indicator is built on the basis of a cross correlation function so that time lags of just a few days between observed and predicted values do not affect it. The model performed adequately, especially for the wet months where its accuracy reached levels greater than 75% implying that daily variability in rainfall height can be to some extent described in the frequency domain.
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