1,720,958 research outputs found
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
High-resolution UAV remote sensing for complex aquatic environments: from planning to data processing
No full textDOTTORATOIl declino globale delle zone umide e degli ecosistemi delle acque interne,
causato dal disturbo antropico e dai cambiamenti climatici, sta portando
un grave deterioramento ecologico e alla perdita di servizi ecosistemici
essenziali. In quanto componente funzionale chiave, la vegetazione acquatica
è gravemente colpita dal degrado degli habitat, danneggiando la biodiversità
e i processi ecologici connessi. Pertanto, il monitoraggio delle dinamiche
della vegetazione acquatica è importante per comprendere la sua risposta ai
fattori di stress ambientale e per aiutare gli sforzi di ripristino. Sebbene i progressi
nelle tecniche di telerilevamento, in particolare per piattaforme drone
(Unmanned Aerial Vehicles, UAV) equipaggiate con sensori iperspettrali, forniscano
strumenti preziosi con risoluzioni spaziali e spettrali senza precedenti,
la loro applicazione negli ecosistemi acquatici rimane poco esplorata, a causa
di diverse sfide e limitazioni. L’obiettivo della presente tesi è identificare i
potenziali fattori di distorsione radiometrica e geometrica nelle immagini iperspettrali
da UAV, e sviluppare metodi per mitigarli, migliorando l’accuratezza
e l’affidabilità dei dati nelle zone umide. Riguardo le distorsioni radiometriche,
abbiamo investigato come le condizioni di illuminazione e le configurazioni
angolari durante i voli UAV contribuiscono a potenziali distorsioni
nelle quantità derivate dalla riflettanza (Capitolo 2). E’ stato riscontrato che il
cielo nuvoloso riduce la riflettanza spettrale nelle bande altamente riflettenti,
in particolare per le piante flottanti. In generale, questo effetto diminuisce il
valore di indici spettrali (Spectral Index, SI) rispetto alle condizioni di cielo
sereno, con minor impatto per l’ indice Normalized Difference Vegetation Index (NDVI). I risultati hanno rivelato che bassi valori di angolo solare zenitale
(Sun Zenith Angle, SZA) e angolo relativo azimutale (Relative Azimuth Angle,
RAA) causano anisotropia spettrale nel range del visibile (visible, VIS),
con un incremento di riflettanza in porzioni specifiche dell’immagine, in base
ai gruppi funzionali. Le piante flottanti hanno mostrato un aumento di riflettanza
nella direzione forward, mentre la vegetazione emergente riflette maggiormente
in direzione backward, coerente con i pattern comuni nella vegetazione
terrestre. NDVI rimane più stabile SI rispetto alla variazione della
configurazione angolare sole-target-sensore. Sulla base di questi risultati, abbiamo
eseguito un esperimento empirico, concentrato sulla mitigazione delle
distorsioni dovute alla configurazione angolare sole-target-sensore durante i
sorvoli UAV (Capitolo 3). Abbiamo riscontrato che il posizionamento laterale
del sole e gli angoli elevati sopra l’orizzonte, causano distorsioni spettrali più
elevate. Per la vegetazione flottante, l’anisotropia spettrale si è verificata sia a
scala fogliare che di chioma, influenzata dalla riflessione quasi speculare della
superficie d’acqua, che funge da substrato o da goccioline sopra le foglie. Al
contrario, la vegetazione emergente dimostra un’aumento di riflettanza della
direzione backward solo a scala di chioma, attribuito all’effetto shadow-hiding
comunemente visibile nelle chiome terrestri. I sorvoli UAV effettuati in momenti
diversi hanno dimostrato che, transitando ad una condizione di azimuth
solare consistente con la direzione di volo (RAA ±90°), oppure volando sotto
un angolo più alto di SZA (> 60°), riduce gradualmente l’anisotropia spettrale,
minimizzando distorsioni significative. Riguardo le distorsioni geometriche
abbiamo introdotto AQUA-LIDAR, un approccio innovativo per la ricostruzione
di un modello digitale di superficie (Digital Surface Model, DSM)
ad alta risoluzione, utilizzando dati LiDAR (Light Detection and Ranging),
come input ausiliario per l’ortoproiezione dei dati iperspettrali (Capitolo 4). Il
metodo ha utilizzato le caratteristiche derivate dal LiDAR per mappare i pixel
della superficie dell’acqua ed estrarre i valori di elevazione corrispondenti,
e usa l’informazione per riempire i buchi del DSM in corrispondenza di altri
pixel appartenenti alla superficie d’acqua. L’approccio ha dimostrato un’ accuratezza
superiore nella ricostruzione delle elevazioni del DSM, in particolare
ai confini dell’acqua, superando i prodotti open-source disponibili. Infine, abbiamo
esaminato l’effetto dell’utilizzo di un DSM ad alta risoluzione rispetto
ad una superficie planare per l’ortoproiezione di immagini iperspettrali, in termini
di errore di georeferenziazione (Capitolo 5). L’analisi ha evidenziato che
l’inclinazione della piattaforma (angolo di rollio) e l’altezza di volo sono le
principali fonti di potenziali distorsioni geometriche. Inoltre, anche l’interazione tra la topografia del terreno e la direzione di scansione contribuisce alle
imprecisioni geometriche, anche in aree prevalentemente pianeggianti. Nel
complesso, la tesi indaga sulle potenziali distorsioni nei dati iperspettrali UAV
per ecosistemi acquatici, concentrandosi sull’accuratezza radiometrica e geometrica.
Oltre ad identificare questi problemi, propone soluzioni pratiche
per mitigarli e correggerli, fornendo anche una preziosa guida operativa sulle
pratiche ottimali di acquisizione ed elaborazione dei dati, in condizioni ambientali
complesse. Inoltre, questo lavoro getta le basi per la ricerca futura,
con l’obiettivo di sviluppare soluzioni di monitoraggio più efficaci verso la
protezione e la conservazione delle zone umide.The global decline of wetlands and inland water ecosystems, driven by
human disturbance and climate change, is leading to severe ecological
deterioration and loss of essential ecosystem services. As a key functional
component, aquatic vegetation is heavily impacted by habitat degradation,
harming biodiversity and connected ecological processes. Therefore,
monitoring aquatic vegetation dynamics is important for understanding its response
to environmental stress and aiding restoration efforts. While advancements
in remote sensing, particularly for Unmanned Aerial Vehicles (UAV)
equipped with hyperspectral sensors, provide valuable tools with unprecedent
spatial and spectral resolutions, their application in aquatic ecosystems remains
underexplored, due to several challenges and limitations. The aim of
this thesis is to identify potential radiometric and geometric distorting factors
in UAV hyperspectral imaging, and to develop methods to mitigate them, enhancing
data accuracy and reliability in wetlands. Dealing with radiometric
distortions, we investigated how illumination conditions and angular configurations
during UAV flights contribute to potential distortions in reflectancebased
quantities (Chapter 2). Overcast sky was found to reduce spectral reflectance
in highly reflective bands, particularly for floating plants. Overall,
this effect lowers Spectral Indices (SI) values compared to clear sky, with
lower impacts on the Normalized Difference Vegetation Index (NDVI). Findings
revealed that low values of Sun Zenith Angle (SZA) and Relative Azimuth
Angle (RAA) caused spectral anisotropy in the visible, with increasing
reflectance in specific image regions, depending on plant functional types. Floating plants showed increased reflectance towards forward direction, while
emergent vegetation reflected more in backward direction, consistent with
common patterns in terrestrial vegetation. NDVI remained the most stable
SI versus sun-target-sensor angular configuration changes. Building on these
findings, we performed an empirical experiment focused on mitigating biases
from sun-target-sensor angular configuration during UAV flights (Chapter
3). We found that lateral sun positioning and high angles above the horizon,
caused higher spectral distortions. For floating vegetation, spectral anisotropy
occurred at both leaf and canopy scale, influenced by water near-specular reflection,
acting as a canopy background or droplets on leaves. In contrast,
emergent vegetation showed increased reflectance in backward direction only
at canopy level, attributed to shadow-hiding effect commonly seen in terrestrial
canopies. UAV flights conducted at different times revealed that transitioning
to a sun azimuth consistent with flight direction (RAA ±90°), or
flying under a higher SZA (> 60°), gradually reduced reflectance anisotropy,
minimizing significant biases. Dealing with geometric distortions we introduced
AQUA-LIDAR, a novel approach for high-resolution Digital Surface
Model (DSM) reconstruction using Light Detection and Ranging (LiDAR)
data, as ancillary input for hyperspectral data ortho-projection (Chapter 4).
The method used LiDAR derived features for mapping water pixel and extract
the corresponding elevation values, and used the information to fill DSM
gaps over other water classified pixels. The approach demonstrated superior
accuracy in DSM elevation reconstruction, especially at water boundaries, outperforming
available open-source products. Finally, we examined the effect of
using a high-resolution DSM versus a planar surface for hyperspectral imagery
ortho-projection, in terms of georeferencing errors (Chapter 5). The analysis
highlighted that the platform’s tilt (roll angle) and flight altitude were primary
sources of potential geometric distortion. Additionally, terrain topography and
scan direction interactions also contributed to geometric inaccuracies, even in
predominantly flat areas. Overall, the thesis investigates potential distortions
in UAV hyperspectral data for aquatic ecosystems, focusing on radiometric
and geometric accuracy. Beyond identifying these issues, it proposes practical
solutions to mitigate and correct them, also providing valuable operational
guidance on optimal data acquisition and processing, in challenging environmental
conditions. Furthermore, this work establishes a foundation for future
research, finally aimed at developing more effective monitoring solutions towards
wetland protection and conservation.DIPARTIMENTO DI INGEGNERIA CIVILE E AMBIENTALEEnvironmental and Hydraulic Engineering and Geomatics37VENUTI, GIOVANNARIVA, MONIC
Mappatura di aree percorse dal fuoco in ambiente mediterraneo mediante un approccio fuzzy applicato ad immagini Sentinel-2
No full textLAUREA MAGISTRALEImmagini satellitari Sentinel-2 Multi-Spectral-Instrument (MSI) vengono utilizzate per mappare le aree bruciate nei confini del Parco Nazionale del Vesuvio durante l’estate del 2017. L’algoritmo implementato in logica fuzzy si discosta dai precedenti che utilizzano dati Landsat, in quanto sfrutta le bande spettrali S-2 per la calibrazione dell’algoritmo in termini di riflettanza post-evento (POST) e differenza temporale di riflettanza (pre- e post-evento, DELTA). Inoltre vengono definite delle funzioni fuzzy di Membership (MF) o di appartenenza alla classe di bruciato, che associano a ciascun pixel un grado di appartenenza alla classe bruciato nel dominio [0,1]. Le bande spettrali, o features in input alle funzioni fuzzy vengono selezionate in base alla loro capacità di discriminare le aree bruciate dalle aree non bruciate (analisi di separabilità). Per ogni features viene definita una MF basata sui valori dei percentili delle distribuzioni dei dati delle aree bruciate e non bruciate. Dopo aver definito le MF queste vengono applicate all’immagine satellitare S-2 per ottenere una mappa di evidenze parziali, variabile in [0,1] di appartenenza alla classe di bruciato (Membership Degree, MD). Ciascuna delle mappe di evidenza parziale viene data in input ad operatori di aggregazione Ordered Weighted Averaging (OWA). Differenti operatori vengono applicati per rappresentare una diversa attitudine dell’operatore nel valutare le aree bruciate: da pessimistica a ottimistica. Il risultato dell’aggregazione mediante OWA è uno score sintetico di MD, o evidenza globale, in [0,1]. Le mappe di evidenza globale saranno successivamente confrontate con il riferimento Copernicus EMSR213 e verranno analizzate le metriche di accuratezza (errore di omissione, commissione e coefficiente di Dice). I risultati mostrano un’accuratezza soddisfacente per la detezione delle aree severamente bruciate da incendio soprattutto per l’operatore OWA quasi OR. Infine verrà testata l’esportabilità dell’algoritmo che sarà applicato in un’area percorsa dal fuoco in Portogallo.Sentinel-2 Multi-Spectral Instrument (MSI) (S-2) images have been used for mapping burned areas within the borders of the Vesuvius National park, severity affected by fires during summer 2017. A fuzzy algorithm, previously developed for Mediterranean ecosystems and Landsat data, have been adapted and applied to S-2 images. Major improvements with respect to the previous algorithm characteristics are the use of S-2 band reflectance in post-fire images and as temporal difference (delta pre- and post-fire); the definition of fuzzy membership function based on statistical percentiles derived from training areas. Input bands were selected based on their ability to discriminate burned vs. unburned areas. For each input, a sigmoid function has been defined based on percentiles of the unburned and burned histogram distributions, respectively, derived from training data. After the definition of fuzzy Membership functions (MF) they’re applied to the S-2 images in order to find the Membership Degree (MD), or the probability to belong to the burned class. Input membership degrees for the selected bands have been integrated to derived pixel-based synthetic scores of burned likelihood with Ordered Weighted Averaging (OWA) operators. Different operators were tested to represent different attitudes/needs of the stakeholders between pessimistic and optimistic way. Output score maps provided as continuous values in the [0,1] domain have been segmented to extract burned/unburned areas; the performance of the combined threshold and OWA operator has been evaluated by comparison with Copernicus fire damage layers from the Emergency Management Service (EMS) (https://emergency.copernicus.eu/). Error matrix, omission, commission error and Dice coefficient metrics have been analysed. Results show satisfactory accuracy is achieved for the identification of the most severely affected areas while lower performance is observed for those areas identified as slightly damage and probably affected by fires of lower intensity. Then the same algorithm is implemented in another burned area situated in Portugal and the exportability is tested
Exploring spectral and phylogenetic diversity links with functional structure of aquatic plant communities
No full textAs freshwater ecosystems are threatened globally, the conservation of aquatic plant diversity is becoming a priority. In the last decade, remote sensing has opened up new opportunities to measure biodiversity, especially across terrestrial biomes, and the combination of spectral features with additional information derived from community phylogeny can further advance the accurate characterisation of plant functional diversity across scales. In this study, we explored the use of spectral features extracted from centimetre resolution hyperspectral imagery collected by a drone and phylogenetic metrics derived from a fully resolved supertree to estimate functional diversity (richness, divergence, and evenness) using non-linear parametric and machine learning models within communities of floating hydrophytes and helophytes sampled from different sites. Our results show that all three functional diversity metrics can be estimated from spectral features using machine learning models (random forest; R2 = 0.90–0.92), while parametric models perform worse (generalised additive models; R2 = 0.40–0.79), especially for community evenness. Merging phylogenetic and spectral features improves modelling performance for functional richness and divergence (R2 = 0.95–0.96) using machine learning, but only significantly benefits community evenness estimation when parametric models are used. The combination of imaging spectroscopy and phylogenetic analysis can provide a quantitative way to capture variability in plant communities across scales and gradients, to the benefit of ecologists focused on the study and monitoring of biodiversity and related processes
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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