1,720,970 research outputs found
Joint exploitation of spaceborne SAR images and GIS techniques for urban coherent change detection
No full textThis paper proposes a simple and fast method for the identification of structural changes affecting buildings in urban environments by using a combination of Synthetic Aperture Radar (SAR) imagery and Geospatial Information System (GIS) processing. The identification of changes in urban settlements is of great interest for damage assessment after natural disasters, cadastral mapping and monitoring urban development or illegal activities, such as the construction of unauthorized buildings. Satellite remote sensing is useful in this scenario and SAR data is attractive due to its wide and ubiquitous coverage, the day and night all-weather availability, the exact repetition of the acquisition geometry, the repeated illumination and the sensitivity to slight changes in the geometrical structure of the targets in the scene. This sensibility is an advantage, but turns into a drawback especially in an urban environment where every subtle change may cause an unwanted detection. This environment is indeed one of the most challenging for the detection of those changes that are of any real interest since these events are masked by thousands of irrelevant detections. This paper tackle this problem with a combination of an improved, high-resolution coherent change detection technique called M-CCD and with a GIS post-processing. The result is a map of changes affecting buildings that are of a significant scale and consequently of a certain interest in an urban environment. In this contribution, the complete workflow is detailed and an assessment of the detected changes is done with high resolution optical images through visual photo-interpretation. A comparison with other SAR and optical change detection methods is also carried out
High-resolution SAR coherent change detection in urban environment
Full text linkThe identification of changes in urban settlements is of great interest for damage assessment after natural disasters, cadastral mapping and monitoring urban development and illegal activities. Radar-based remote sensing from space-borne platforms is quite useful in this scenario and Synthetic Aperture Radar (SAR) data is attractive due to its wide coverage, the day and night all-weather availability, and the sensitivity to slight changes in the scene structure. In this context, the launch of the European Space Agency (ESA) constellation Sentinel-1 has played a significant role: the exact repetition of the acquisition geometry, the repeated illumination and the sensitivity to centimetric changes thanks to the C-Band (5.4GHz) radar payload make Sentinel-1 the perfect instrument to monitor urban settlements. Coherent Change Detection (CCD) techniques are able to detect even the finest change in the structure of a target, so small to be comparable with the wavelength. This sensibility is an advantage, but turns into a drawback especially in an urban environment where every subtle change may cause an unwanted detection. This paper tackles the problem of the huge amount of triggered detections over urbanized areas with a combination of a high-resolution coherent multi-change detection technique and Geospatial Information System (GIS) post-processing. The final result is a map of buildings that are changed in the scene due to relevant variation of their structure. In this contribution, the complete workflow is explained, and a preliminary validation is carried out by means of a set of images gathered by Sentinel-1 and a set of optical images over the city of Manchester.
A novel index for temporal stability analysis in space and time of sar-derived scenes
Full text linkDetecting temporal changes is one of the most important applications of satellite sensors. In recent years, the increasing availability of regular time-series of SAR imagery, provided by the Sentinel-1 mission of the European Space Agency (ESA), has drawn increasing attention to these techniques, especially in earth environment monitoring and risk management. Within this paper, a coherent change detection analysis for evaluating the risk due to movements of dunes and sand sheets in desertic areas is proposed. To this purpose, we introduce a novel, coherence-based index, named Temporal Stability Index (TSI), that is suited for characterizing the percentage of stability of a target with time. TSI maps can be generated over areas as wide as hundreds of kilometers, in a short time, and mostly by exploiting available software tools (plus some simple coding). The information provided is complementary to the average of the short-term coherence, here shown. Results of analysis performed on two desertic regions (the United Arab Emirates and Egypt) document the usefulness of TSI for the identification of dune movements and areas subject to sand accumulation, supporting risk mitigation measures
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
A FREE AND OPEN SOURCE TOOL TO ASSESS THE ACCURACY OF LAND COVER MAPS: IMPLEMENTATION AND APPLICATION TO LOMBARDY REGION (ITALY)
Full text linkThe availability of thematic maps has significantly increased over the last few years. Validation of these maps is a key factor in assessing their suitability for different applications. The evaluation of the accuracy of classified data is carried out through a comparison with a reference dataset and the generation of a confusion matrix from which many quality indexes can be derived. In this work, an ad hoc free and open source Python tool was implemented to automatically compute all the matrix confusion-derived accuracy indexes proposed by literature. The tool was integrated into GRASS GIS environment and successfully applied to evaluate the quality of three high-resolution global datasets (GlobeLand30, Global Urban Footprint, Global Human Settlement Layer Built-Up Grid) in the Lombardy Region area (Italy). In addition to the most commonly used accuracy measures, e.g. overall accuracy and Kappa, the tool allowed to compute and investigate less known indexes such as the Ground Truth and the Classification Success Index. The promising tool will be further extended with spatial autocorrelation analysis functions and made available to researcher and user community
VALIDATION OF THE GLOBAL HIGH-RESOLUTION GLOBELAND30 LAND COVER MAP IN EUROPE USING LAND COVER FIELD SURVEY DATABASE - LUCAS
Full text linkHigh-resolution land cover maps are one of the technological innovations driving improvements in many fields influenced by Geographic Information Systems (GIS) and Remote Sensing. In particular, the GlobeLand30 (GL30), global LC map with spatial resolution of 30 m, is thought to be one of the highest quality high-resolution products. However, these LC maps require validation to determine their suitability for a particular purpose. One of the best ways to provide useful validation reference data is to do a high-level accuracy field survey, but this is time consuming and expensive. Another option is to exploit already available datasets. This study assesses thematic accuracy of GL30 in Europe using LUCAS as a validation reference, because it is a free and open field survey database. The results were generally not good, and very bad for some classes. Analysis was then restricted to a small region (Lombardy, Italy) where LC data of higher resolution than those of GL30 were available. LUCAS was also found to be incoherent with this product. Further comparisons of LUCAS with other independent sources confirmed that the LC attributes of LUCAS are inconsistent with expectations. Although these findings may not be generalized to other regions, the results warn against the suitability of LUCAS as ground truth for LC validation. The paper discusses the process of thematic accuracy assessment of the GL30 and the applicability of LUCAS for high-resolution global LC validation
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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