1,721,211 research outputs found
Gathering SAR data under different bistatic angle: a new potential of COSMO/SkyMed constellation
No full textModifications required to a SAR constellation mission are addressed in order to achieve bistatic observations under a range of bistatic angles, in a cost effective and flexible fashion. In particular, the paper investigates achievable performance deriving from an evolution of COSMO/SkyMed towards bistatic applications. A mathematical model is presented, which allows evaluation of bistatic angles as a function of latitude and longitude, on the basis of orbits’ propagation and spherical trigonometry. Results show that while nodal separation increases, a target is observed under a variable bistatic angle, which is not an increasing monotonic function of time due to the varying position of orbits’ intersections and thanks to electronic beam steering capability
Relative motion model including J2: derivation and application to INSAR
No full textIn the growing field of formation flying, most models in literature are devoted to control problems rather than to the issue of designing the orbits on the basis of mission requirements. In this paper, the authors present an analytical model which allows a time-explicit representation
of relative motion on the basis of orbital parameters’ differences between satellites, in the case of a reference satellite moving on a circular or slightly eccentric orbit. Both derivations take into account secular Earth oblateness effects. Numerical analyses show that, in typical cases of interest, equations’ errors are of the order of 0.1% of
relative motion coordinates, and grow very slowly with time. Application of the derived model to interferometric and bistatic missions proposed in literature allows to rediscover and better interpret results of numerical optimization of given formations, and to point out possibilities deriving from the evolution of relative
trajectory
Innovative method of constellation design to enable new arising applications based on space-airborne bistatic SAR
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Future Trend, Potential, Risks
No full textDuring the last decades, the concept of distributed space systems has
significantly progressed in terms of space applications, including Earth remote sensing. This chapter is devoted to a critical analysis of the achieved improvements and of the areas of major key issues in order to analyze potential and risks of distributed space systems. A discussion of future activities needed to prepare more advanced distributed space missions is also provided. In particular, payloads and
applications are first discussed. Then, guidance, navigation, and control as well as other technological challenges, including modularity and architecture, follow
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
ANALYSIS OF FORMATION GEOMETRIES FOR MULTISTATIC SAR INTERFEROMETRY AND TOMOGRAPHY
No full textThis paper analyzes relative orbit design for multi-satellite radar missions aimed at multistatic SAR tomography. To this end, formation requirements and performance parameters are derived by adapting existing models for SAR tomography to single pass techniques. Then, relative trajectory designed is carried out on the basis of an analytical relative motion model including secular J2 effects. By properly scaling the differences in orbital parameters, different formation geometries enable uniform sampling of the effective baseline along the whole orbit. The difference among the possible choices lies in latitude coverage, formation stability, and collision avoidance aspects. A numerical example of relative trajectory design is discussed considering L-band as operating frequency. In particular, achievable height resolution and unambiguous height along the orbit are pointed out for a multi-cartwheel, a multi-pendulum, and a multi-helix formation
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