1,720,960 research outputs found
Understanding effects of atmospheric variables on spectral vegetation indices derived from satellite based time series of multispectral images
No full textIn agricultural practices, it is very essential to monitor crops phenological pattern over the time to manage agronomic activities such as irrigation, weed control, pest control, fertilization, drainage system etc. From the past decade, due to free availability of data and large coverage area, satellite based remote sensing has been most popular and widely used among other techniques such as physical ground surveys, ground based sensors and aerial based remote sensing. Sentinel-2 is European based satellite equipped with the state of the art multispectral imager which offers high spectral resolution (13- spectral bands), high spatial resolution (up to 10m pixel -1 ) and good temporal resolution (6 to 10days). Considering these features, time series of multispectral images of sentinel-2 has been used to establish temporal pattern of spectral vegetation indices (i.e. NDVI, SAVI, EVI, RVI) of crops to monitor the phenological behavior over time. In addition, the influence of various atmospheric variables (such as temperature in the air and precipitation ) on the derived spectral vegetation indices has also been investigated in this work. Land use and coverage area frame survey (LUCAS-2015) has been used as ground reference data for this study. This study shows that by using sentinel-2, understanding relation between atmospheric conditions and crops phenological behavior can be useful to manage agricultural activities
Analyzing relationship between maize height and spectral indices derived from remotely sensed multispectral imagery
No full textFor maize crop, biophysical parameters such as canopy height and above ground biomass are the crucial agro-ecological indicator that can be used to describe the crop growth, photosynthetic efficiency and carbon stock. Remote sensing is widely used approach and most appropriate source in terms of area coverage that can be used to monitor vegetative conditions over the large area. In this study, sentinel-2 multispectral imagery is used to calculate spectral vegetation indices over the different maize growth period using some visible bands including near infrared spectrum. The relationship has been established and analyzed between maize biophysical variables (height of the canopy and above ground biomass) collected during the field measurements and derived spectral vegetation indices using simple linear regression and pearson correlation to exploit the possibility of using satellite imagery for estimation of crop biophysical parameters
Reliability of the geometric calibration of an hyperspectral frame camera
Full text linkOne of the main tools for high resolution remote sensing and photogrammetry is the lightweight hyperspectral frame camera, that is used in several application areas such as precision agriculture, forestry, and environmental monitoring. Among these types of sensors, the Rikola (which is based on a Fabry–Perot interferometer (FPI) and produced by Senop) is one of the latest innovations. Due to its internal geometry, there are several issues to be addressed for the appropriate definition and estimation of the inner orientation parameters (IOPs). The main problems concern the possibility to change every time the sequence of the bands and to assess the reliability of the IOPs. This work focuses the attention on the assessment of the IOPs definition for each sensor, considering the impact of environmental conditions (e.g., different time, exposure, brightness) and different configurations of the FPI camera, in order to rebuild an undistorted hypercube for image processing and object estimation. The aim of this work is to understand if the IOPs are stable over the time and if and which bands can be used as reference for the calculation of the inner parameters for each sensor, considering different environmental configurations and surveys, from terrestrial to aerial applications. Preliminary performed tests showed that the focal length percentage variation among the bands of different experiments is around 1%
Geometrical 3D model generation of rock blocks using low-cost photogrammetry [Article@Ricostruzione geometrica 3D di blocchi di roccia mediante fotogrammetria low cost]
No full textICE DETECTION on AIRPLANE WINGS USING A PHOTOGRAMMETRIC POINT CLOUD: A SIMULATION
Full text linkThis study describes some tests carried out, within the European project (reference call: MANUNET III 2018, project code: MNET18/ICT-3438) called SEI (Spectral Evidence of ice), for the geometrical ice detection on airplane wings. The purpose of these analysis is to estimate thickness and shape of the ice that an RGB sensor is able to detect on large aircrafts as Boeing 737-800. However, field testing are not available yet, therefore, in order to simulate the final configuration, a steel panel has been used to reproduce the aircraft surface. The adopted methodology consists in defining a reference surface and modelling its 3D shape with and without ice through photogrammetric acquisitions collected by a DJI Mavic Air drone hosting a RGB camera and processed by Agisoft Metashape software. The comparison among models with and without the ice has been presented and results show that it is possible to identify the ice, even though some noise still remains due to the geometric reconstruction itself. Finally, using 3dReshaper and Matlab software, the authors develop various analysis defining the operative limits, the processing time, the correct setting up of Metashape for a more accurate ice detection, the optimization of the methodology in terms of processing time, precision and completeness. The procedure can certainly be more reliable considering the usage of the hyperspectral sensor technique as future implementation
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
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
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