1,720,969 research outputs found
Application For Shadow Removal From Geo Eye-1 RGB Composition
No full textShadow is a phenomenon that can’t be avoided and the effects are evident in high resolution images. Humans easily identify shadows, but it is harder to automatically recognize them with detection algorithm because there are a lot of factors that can influence the quality of the result. In this paper the problem of shadow detection and removal is treated for multispectral data of the GeoEye-1 satellite (geometric resolution: 2 m; bands: Blue, Green, Red, Near Infrared). The considered scene includes urban area where shadows originated by buildings and trees are present. An index, named RATIO, is computed using Near Infrared and Blue bands to highlight the affected areas in the images. To restore the luminance of shadow zones the radiometric enhancement technique named Gamma Correction is used
Advantages of Multi GNSS Constellation: GDOP Analysis for GPS, GLONASS and Galileo Combinations
Full text linkPositioning techniques made lots of progress in the last decades, thanks to the wide usage of the Global Navigation Satellite Systems (GNSS). During a satellite survey, interruption or complete absence of positioning service can happen due to obstacle presence or constrained environments. To avoid these problems, it is suitable to simulate a positioning survey determining the number of the GNSS satellites in view and their availability trend for a selected location. Using more than one constellation the number of the observed satellites is increased and the continuity and reliability of positioning significantly improved. The aim of this paper is to assess the impact of multi-GNSS constellation on positioning calculation in terms of number of available satellites and geometrical distribution in the sky. A simulation is conducted for different cut-off angles, ranging from 0° to 30°: satellites visibility predictions are performed for the city of Benevento (Italy) using short observing sessions (96 daily) and considering GPS, GLONASS and GALILEO constellation. The benefits of their combinations are investigated: in order to assess the observation quality, the Geometrical Dilution of Precision (GDOP) is used as criteria to prove how it is possible to reduce degradation of the position accuracy by using multi-GNSS combinations. Particularly, GPS+GLONASS supplies higher performances compared to the other solutions. Because the low number of satellites in view, the contribution of GALILEO is limited, and its presence instead of GPS or GLONASS in the two constellation solutions produces a decrease in positioning accuracy
A New Index to Perform Shadow Detection in GeoEye-1 Images
No full textWith the introduction of new satellites for earth monitoring characterized by very high
resolution (VHR) sensors, new algorithms to recognize shadow in the supplied images are necessary.
Automatic shadow detection can enhance the interpretability of the images in several applications such as
classification and change detection. Several approaches are present in literature for shadow detection and
their adaptation and particularization for VHR satellite images are still in evolution. The goal of this
paper is to propose a new index for shadow detection based on multispectral files processing. GeoEye-1
satellite data are used for this study: IHS pan-sharpening method is applied to transfer pixel dimensions
of the panchromatic image (spatial resolution: 0.5 m x 0.5 m) into the multispectral images (2 m x 2 m);
an index named ERGAS is used to test the quality of the resulting raster files. Dealing with the problem
of the shadow detection, a new index is defined to identify the affected pixels both in the original as well
as pan-sharpened images. The results are compared with them by another index named ratio that is
generally applied for shadow detection in multispectral images: issues and advantages, derived by using
the proposed technique, are discussed
Application of different pan-sharpening methods on WorldView-3 images
No full textIn the field of the remote sensing, the introduction of high resolution satellite sensors has required the
development of several data fusion approaches. Two kinds of images are usually acquired: multispectral and panchromatic.
The first group has a lower spatial resolution but accurate spectral information while the second presents a higher spatial
resolution with a longer band acquisition range. Pan-sharpening permits to combine panchromatic and multispectral data to
create new multispectral images with higher geometric resolution. In this paper nine different pan-sharpening methods are
tested on WorldView-3 images: Brovey, Weighted Brovey, Gram Schmidt, IHS, Fast IHS, Multiplicative, Principal
Component Analysis (PCA), Simple Mean and Zhang. With the aim to rank the techniques efficiency, visual inspections
combined with quantitative evaluations are performed to test spectral qualities of the fused images. This is a difficult task
because the quality of the fused image depends on the considered datasets: RMSE (Root Mean Square Error) and ERGAS
(Relative Dimensionless Global Error) are the accuracy indices used for this scope
Comparison of Methods for IKONOS Images Pan-sharpening Using Synthetic Sensors
No full textAbstract: Many methods are present in literature for pan-sharpening of satellite images: they permit to transfer
geometric resolution of panchromatic data to multispectral ones, but the results of their application are different. To
evaluate the quality of these products, visual analysis is carried out, above all on the RGB composition to detect
colour distortion. To quantize the level of similarity of the pan-sharpened images with them that should be achieved
with effective more effective sensors, several indices are available such as: RMSE, correlation coefficients, UIQI,
RASE. The principal limit of these indices consists in the terms of comparison because they compare the pansharpened
images with the original ones that are with lower resolution. To supply the unavailability of the effective
dataset with the same pixel dimensions of the pan-sharpened files, synthetic sensors can be introduced with lower
resolution than the original ones. The correspondent degraded images can be submitted to pan-sharpening process
and the results can be considered performed if similar to the original multispectral dataset. In this study IKONOS
synthetic sensors are introduced to compare different methods: transforming the digital numbers into the radiance of
the earth surface, original images of Campania Region are degraded and then submitted to some pan-sharpening
approaches. The following methods are considered: multiplicative, simple mean, IHS, Fast IHS, Brovey, Weighted
Brovey, Gram Schmidt, Zhang. Each resulting dataset is compared with the original multispectral one to evaluate
the performance of each method
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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