1,720,999 research outputs found
A Far Range Image Processing Method for Autonomous Tracking of an Uncooperative Target
Full text linkThis paper proposes an image processing method for far range rendezvous. A target spacecraft at distances up to ~km is tracked from camera images. The method is based on linking bright, connected sets of pixels over sequences of images. Stars and the target spacecraft are identified by using a star catalog and performing motion segmentation. The algorithm is illustrated in detail and
%the visibility of stars and of the target are analyzed which is a prerequisite to perform far range image processing. Further,
results of a flight experiment called ARGON are presented. The experiment took place in the extended phase of the PRISMA mission. The image processing method was employed and a successful rendezvous from ~km to ~km was accomplished using optical navigation
Flight Demonstration of Non-Cooperative Rendezvous using Optical Navigation
No full textThe ultimate goal of this work is to demonstrate the capability of a maneuverable servicer spacecraft to rendezvous with a non-cooperative space resident object from far-range distance using optical angles-only measurements. To this end, the Advanced Rendezvous experiment using GPS and Optical Navigation (ARGON) has been executed during the extended phase of the PRISMA formation-flying mission in April 2012. This paper addresses the experiment design, the developed flight dynamics system, the obtained flight results, and the lessons learned. Furthermore the evaluation of the rendezvous tracking, navigation and control accuracy is performed by means of GPS-based precise relative orbit determination products. The presented results give a clear demonstration of the high readiness level reached by key technologies which are needed by future on-orbit servicing and debris-removal missions
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
End-to-End Simulation and Verification of Rendezvous and Docking/Berthing Systems using Robotics
No full textThe rendezvous and docking/berthing (RvD/B) phase is one of the most complex and critical parts of future on-orbit servicing missions. Especially the operations during the final approach (separation distance < 20m) have to be verified and tested in detail. Such tests involve on-board systems, communication systems and ground systems.
In the framework of an end-to-end simulation of the final approach to and capture of a tumbling client satellite, the necessary components are developed and the entire chain will be tested and verified.
Concerning the on-board system, this involves the robotic arm for grasping the client, a stereo camera for visual servoing mounted on the robotic arm, the rendezvous sensors (CCD camera and LiDAR), and the on-board navigation and control software.
A software satellite simulator is employed which emulates the physical environment of the two spacecraft. Two robotic test facilities, the European Proximity Operations Simulator (EPOS 2.0) at DLR-GSOC and the OOS Grasping Simulator (OOS-Sim) at DLR-RMC are used. The
hardware components are mounted on the robots of the two facilities. The robots move according to the resulting relative position and orientation of the two satellites computed by the numerical satellite simulator.
The communication infrastructure is simulated, and the ground infrastructure is established including three consoles: a standard satellite bus console, a rendezvous console and a robotic console.
Finally, a series of end-to-end tests will be conducted; different approaches will be simulated. The first part, the approach to the final hold point will be performed using the EPOS facility. Then a switch to the OOS-Sim facility will be done, followed by a capture of the target
Parametric methods for image processing using active contours with topology changes
Full text linkIn this thesis we consider parametric methods for image processing based on active contours. We introduce an efficient scheme for image segmentation by evolving parametric hypersurfaces. More precisely, we present methods for segmentation of 1) two-dimensional, planar images, of 2) images on curved surfaces and of 3) three-dimensional images.
The developed methods can handle complex curve networks with possible triple junctions and intersections of the curves with the image boundary. Also curves with free endpoints are supported. The methods can be used to segment a given image in regions of arbitrary number, separated by hypersurfaces.
Numerically, the evolving curves and surfaces are discretized and the resulting schemes are solved by finite differences and finite elements. We show that the parametric approach for curve evolution in the plane and on surfaces has good properties concerning the equidistribution of mesh points along the discretized curves. For evolving surfaces, we observe problems with the quality of the triangulated meshes in rare cases only. We propose a method for an efficient mesh regularization which is incorporated into the evolution scheme for surfaces.
Standard parametric approaches cannot automatically handle topology changes like splitting and merging of curves and surfaces, creating and deleting triple junctions and boundary intersection points of curves as well as changing the genus of a surface. Therefore, we introduce an efficient method to detect and execute such topology changes. Using our approach, the computational effort to detect a topology change depends only linearly on the number of mesh points.
In addition to image segmentation, we propose a method for edge-preserving image smoothing. The denoising of the image is executed as a postprocessing step, subsequently to the segmentation. Thereby, diffusion equations with Neumann boundary conditions are solved in the already segmented regions. In the case of images defined on surfaces, this results in partial differential equations on manifolds.
Finally, we demonstrate the developed methods on various artificial and real images and show the efficiency of the methods and their application to real, practical image processing tasks arising in medicine, navigation, Earth observation and in many other areas
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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