1,721,111 research outputs found
Automated selection of suitable atmospheric calibration sites for satellite imagery
No full textGround calibration targets (GCTs) play a vital role in atmospheric correction of satellite sensor data in the optical region, but selecting suitable targets is a subjective and time-consuming task. This paper describes a method to automatically select suitable GCTs, using a combination of remotely sensed multispectral and topographic data. Desirable characteristics for GCTs sites were identified from the literature, and used to devise a semi-automated workflow based on programs written in IDL combined with routines offered by ITTVIS ENVI and Definiens eCognition. Spatial statistics were used to assess local patterns of spatial uniformity, and endmember abundances (extracted using the SMACC algorithm) were used in a novel method to ensure a spread of calibration sites throughout the brightness range for each band. The result of this process was a map of candidate GCTs, classified according to their suitabilit
Spatial variability of the atmosphere across southern England and the resulting error in assuming a uniform atmospheric correction
No full textThere is an increasing trend towards the use of large-swath satellite sensors, such as those on the Disaster Monitoring Constellation (DMC), for monitoring environmental change due to their significant advantages over systems such as Landsat. Before imagery can be used quantitatively it must undergo atmospheric correction, where most techniques assume a uniform atmosphere across the image – an assumption that is likely to be invalid for 600km wide images from DMC. To assess the significance of the error caused by this assumption, spatial variability over southern England on a clear day is assessed from a number of data sources and the results are used in simulations with the 6S Radiative Transfer Model to examine the effects on NDVI, and Net Primary Productivity values calculated from these NDVI data using the CASA ecosystem model.Results show that the AOT variation during the study period was approximately 0.1-0.5 and that this could cause an error in NDVI of 2.9-4.5%. A conservative estimate of the error in NPP values which could be caused by this over southern England is 7.6Mt C, or 3%. Further work should focus on spatially-variable atmospheric correction techniques
Automated identification of invariant ground targets: towards a UK environmental change space observatory (UK-ECSO)
No full textWilson, R.T. — Ecophysiology of the Camelidae and Desert Ruminants. Berlin, Heidelberg, New York. Adaptations of Desert Organisms. J.L. Cloudsley-Thompson (Ed.), Springer-Verlag, 1989
No full textGrenot Claude. Wilson, R.T. — Ecophysiology of the Camelidae and Desert Ruminants. Berlin, Heidelberg, New York. Adaptations of Desert Organisms. J.L. Cloudsley-Thompson (Ed.), Springer-Verlag, 1989. In: Revue d'Écologie (La Terre et La Vie), tome 46, n°1, 1991. pp. 92-94
Spatial variability of the atmosphere over southern England, and its effect on scene-based atmospheric corrections
Get PDFEarth observation data acquired in the optical region require atmospheric correction before they can be used quantitatively. Most operational methods of atmospheric correction assume that the atmospheric properties are uniform across the image, but this assumption is unlikely to be valid for large images. This study aims to characterize the spatial variation in atmospheric properties over a typical mid-latitude area (southern England), and to assess the errors that would result from applying a scene-based atmospheric correction to data collected under this variable atmosphere. Two key atmospheric properties – aerosol optical thickness (AOT) and precipitable water content (PWC) – are assessed over two clear days in June 2006, and results show an AOT range of approximately 0.1–0.5 and a PWC range of 1.5–3.0 cm. Radiative transfer modelling shows that errors in reflectance of up to 1.7 percentage points, and up to a 5% change in normalized difference vegetation index, can be caused by AOT variability, but that PWC variability has minimal effects. Sensitivity analyses also show that the high uncertainty of many data sources used to provide AOT values for atmospheric correction may also lead to significant errors in the resulting products. The spatial variability of the atmosphere cannot be ignored, and we are in need of operational, generic methods to perform a spatially variable atmospheric correction
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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