1,721,044 research outputs found
Monitoring of marine litter through remote sensing and hydrodynamic Lagrangian models
Full text linkMarine pollution is a growing global issue. Following the proof of the significant impacts of marine debris on the ecosystem worldwide, in the last decades, the scientific community has focused the efforts on monitoring and detection to assess more effective management strategies. The first efforts were focused on the quantification and characterisation of pollutants, mostly performing in-situ campaigns both in the beach and sea environments. Up to now, the characterisation of the debris fractions has shown that the most commonly portion is represented by plastic items. These polymers are characterised by long residence times and the predisposition to be degraded in smaller items, causing even greater impact on several marine fauna species and, consequently, on humans. Recently, due to the difficulties to perform intensive in-situ sampling campaigns especially over large areas, the growing of new observation technologies has driven the scientific community to develop remote sensing techniques for marine litter detection. Several applications carried out using unmanned aerial vehicles and satellite data highlighted that there is a lack of knowledge about the spectral response of marine litter and plastic items. Additionally, their detection could be also more difficult by considering their temporal evolution due to degradation processes in the marine environment.The issue concerns marine pollution is even worse considering that once at the sea marine litter debris could be drifted by the sea currents to areas which can be very far from the source points. Thus, there is high uncertainty about the areas which can be more impacted by these kinds of pollution both at the sea (accumulation areas) and at the coast (beaching). In this framework, the existing monitoring actions (i.e. in-situ or remote detection) could be not enough to study and thus deal with the marine litter pollution problem.In this context, this thesis has been designed to test, and then to provide new insights into the marine litter issue through an integrated approach which include the in-situ monitoring campaigns, the application of remote sensing techniques following a bottom-up approach, the setup of numerical Lagrangian models to determine areas were these kinds of pollutions could be severe (accumulation and beaching areas). A monitoring campaign conducted in two urban beaches, with different management, allowed to quantify and characterise the pollution status of those areas. Results show the need to manage the beaches, organising frequently beach cleaning activities. Some of the samples collected during the monitoring, have been spectrally characterised via a Laboratory experiment, and the wavelengths/bands useful for the detection as well as the best sensors to use, were identified. Some bands in the visible, red-edge, and in some infrared bands, appear effective for the beach litter detection. WorldView-3 resulted the sensor more useful for this purpose among the nowadays operating satellite platforms.Furthermore, the interconnection between sea and beach environments was studied applying Lagrangian hydrodynamic models able to identify accumulation and beaching area. Outcomes of the models have confirmed as the marine litter is a transboundary issue that only a joint action of the countries can mitigate. Finally, the potentiality of hyperspectral satellite data was tested analysing PRISMA images evaluating the capability to detect an artificial floating target deployed at the Aegean Sea. Results showed that satellite hyperspectral images represent a useful tool for marine litter detection, although their spatial resolution limits their applicability
Marine plastic detection using PRISMA hyperspectral satellite imagery in a controlled environment
No full textThe amount of plastics on seawater is causing ecosystem damage
to both land areas and water bodies. It is proven that once plastic
particles reach the sea, they will be degraded. As their detection is
not easy with in situ sampling, remote sensing techniques could
help detect and evaluate their impact on ecosystems. To under stand the main limitations of detecting floating plastic material
through remote images, an a pilot experiment was carried out on
an artificial floating plastic target deployed at the Aegean Sea
(Greece) within the Plastic Litter Project 2021. Hyperspectral
PRISMA, multispectral PlanetScope and visible Unmanned Aerial
Systems (UAS) acquisitions were analysed. A nonlinear unmixing
technique was applied to derive the spectral signature of the plastic
target; finally, the linear unmixing approach allowed for determin ing the plastic percentage occupation at the pixel level. Different
band combinations of the PRISMA data were selected to evaluate
which provided the best result for the detection; one of these band
combinations was retrieved via the principal component analysis.
Only slight differences were achieved using the different PRISMA
band-sets. As expected, since the artificial plastic target had
a diameter comparable with the PRISMA spatial resolution (~30
m), its detection was a challenging task caused by the water influ ence in the pixel (mixed pixels). The detection was realized by
benefitting from the high amount of available spectral bands, as
confirmed by the comparative test with a PlanetScope image used
at its original spatial resolution (3 m) and after degrading it at the
PRISMA level. Results demonstrated that an optimal target detec tion was possible with few spectral bands, only taking advantage of
the high spatial resolution (compared with the target dimension).
Indeed, unreliable plastic fractions were derived at the PRISMA
spatial resolution with a limited number of spectral bands
Large-Eddy Simulation e tecnica LS-PIV: lo studio della turbolenza superficiale
Full text linkGli avanzamenti tecnologici degli ultimi decenni hanno fatto registrare la rapida diffusione di tecnologie innovative con cui condurre un monitoraggio ambientale più efficiente ed efficace. Nel campo del monitoraggio fluviale sono sempre più utilizzate le tecniche basate sull’elaborazione di immagini, fornendo una valida alternativa alle metodologie tradizionalmente adottate. Le tecniche ottiche restituiscono infatti misure non intrusive, assicurando migliori condizioni di sicurezza per gli operatori. I metodi ottici più utilizzati sono la Large-Scale Particle Image Velocimetry (LS-PIV) [1] e la Large-Scale Particle Tracking Velocimetry (LS-PTV) [2].
Le tecniche LS-PIV e LS-PTV si basano sulla registrazione video del movimento di un tracciante opportunamente introdotto sulla superficie libera di un corso d’acqua assumendo che le particelle traccianti si muovano in maniera solidale con i filetti liquidi superficiali. I dispositivi di registrazione generalmente utilizzati sono costituiti dalle comuni fotocamere digitali, o dai più moderni smartphone, o ancora dai droni. I video risultanti sono successivamente elaborati attraverso software open-source, i quali applicano un’analisi di cross-correlazione statistica al fine di stimare il campo di velocità superficiale istantaneo.
L’obiettivo di questo lavoro è analizzare le performance dei software LS-PIV più largamente utilizzati nella stima del campo di velocità superficiale di un corso d’acqua, tenendo in considerazione la presenza di strutture turbolente. I vortici turbolenti sono elementi frequentemente osservabili nei corsi d’acqua naturali che possono rendere senz’altro complesso il tracciamento degli spostamenti delle particelle traccianti sulla superficie libera. La valutazione dello spostamento di ogni singolo elemento tracciante è resa ancor più difficoltosa dal fenomeno negativo dell’aggregazione tra le particelle, portando spesso a stime incorrette dei vettori velocità.
In questo lavoro, lo studio della turbolenza idraulica di un corso d’acqua naturale è stato condotto da un punto di vista numerico. È stato utilizzato uno dei software di fluidodinamica computazionale più conosciuti, ANSYS Fluent, adottando la Large-Eddy Simulation come schema risolutivo per la turbolenza. ANSYS Fluent risolve le equazioni del moto tridimensionale per fluidi incomprimibili utilizzando il metodo ai volumi finiti. Le analisi sono state condotte su casi reali opportunamente modellati con ANSYS Fluent. I domini idraulici presi in esame sono caratterizzati da sezioni trasversali regolari, accuratamente derivate da campagne di rilievi topografici, e da scabrezze del fondo alveo piuttosto ridotte.
La modellazione numerica ha permesso di derivare diverse sequenze sintetiche del moto del tracciante sulla superficie libera, successivamente elaborate con i software di analisi LS-PIV. I risultati di queste analisi numeriche hanno permesso una valutazione delle performance della tecnica LS-PIV, espresse in termini di errori valutando la velocità media superficiale e le velocità lungo transetti trasversali
Assessing the performance of different model-based techniques to estimate water content in the upper soil layer
Full text linkThe knowledge of soil water content (SWC) of the upper soil layer is important for most hydrological processes
occurring over vegetated areas and under dry climate. Because direct field measurements of SWC are difficult, the
use of different type of sensors and model-based approaches have been proposed and extensively used during the
last decade.
The main objective of this work is to assess the performance of two models estimating SWC of the upper soil
layer: the transient line heat source method and the physically based Hydrus-1D model. The models’ performance
is assessed using field measurements acquired through a Time Domain Reflectometer (TDR).
The experiment was carried out on an olive orchard located near the town of Castelvetrano (South-West of Sicily
- latitude 37.6429◦
, longitude 12.8471◦
). The temporal dynamic of topsoil water content was investigated in two
samplers, under wet and dry conditions. The samplers were opened at the upper boundary and inserted into the
soil to ensure the continuity of the soil surface.
A K2D Pro sensor allowed to measure the soil thermal properties allowing to estimate soil thermal inertia and
then SWC. The physically based Hydrus-1D model was also used to estimate SWC of both samples. Hourly
records of soil water contents, acquired by a TDR100 probe, were used to validate both the considered models.
The comparison between SWCs simulated by Hydrus-1D and the corresponding values measured by the TDR
method evidenced a good agreement. Similarly, even SWCs derived from the thermal diffusion model resulted
fairly close to those measured with the TDR
Validation of HF radar sea surface currents in the Malta-Sicily Channel
No full textA network of High-Frequency radar (HFR) stations runs operationally in the Malta-Sicily Channel (MSC), Central Mediterranean Sea, providing sea surface current maps with high temporal (1 h) and spatial (3 × 3 km) resolutions since August 2012. Comparisons with surface drifter data and near-surface Acoustic Doppler Current Profiler (ADCP) observations, as well as radar site-to-site baseline analyses, provide quantitative assessments of HFR velocities accuracy. Twenty-two drifters were deployed within the HFR domain of coverage between December 2012 and October 2013. Additionally, six ADCP vertical current profiles were collected at selected positions during a dedicated field survey. External radio-frequency interferences lead to significant gaps in the HFR coverage, which were minimized by an interpolation technique applied to the surface current fields. The validation of HFR velocities was first performed for each individual station in the network, using data generated with both the ideal and the measured antenna patterns. The validation was then repeated with pairs of HFR stations using the site-to-site baseline error analysis. The analysis confirms that the baseline error estimations and the full validation metrics for this HFR frequency band are consistent, and in some aspects superior, when compared to results from similar studies in other regions. The validation with drifter tracks suggests that the adopted interpolation procedure does not in general impact on the comparison metrics, but may introduce biases when used to extrapolate currents in regions where radar geometrical constraints are suboptimal. The analysis of the percentage of contribution of individual HFR stations shown that the quality of HFR data is influenced by the network geometry
Downscaling hydrodynamics features to depict causes of major productivity of Sicilian-Maltese area and implications for resource management
No full textChlorophyll-a (CHL-a) and sea surface temperature (SST) are generally accepted as proxies for water quality. They can be easily retrieved in a quasi-near real time mode through satellite remote sensing and, as such, they provide an overview of the water quality on a synoptic scale in open waters. Their distributions evolve in space and time in response to local and remote forcing, such as winds and currents, which however have much finer temporal and spatial scales than those resolvable by satellites in spite of recent advances in satellite remote-sensing techniques. Satellite data are often characterized by a moderate temporal resolution to adequately catch the actual sub-grid physical processes. Conventional pointwise measurements can resolve high-frequency motions such as tides or high-frequency wind-driven currents, however they are inadequate to resolve their spatial variability over wide areas. We show in this paper that a combined use of near-surface currents, available through High-Frequency (HF) radars, and satellite data (e.g., TERRA and AQUA/MODIS), can properly resolve the main oceanographic features in both coastal and open-sea regions, particularly at the coastal boundaries where satellite imageries fail, and are complementary tools to interpret ocean productivity and resource management in the Sicily Channel
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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