17 research outputs found
Method for estimating clutter limited geosynchronous synthetic aperture radar performance
This paper reviews the geosynchronous synthetic aperture radar (GeoSAR) literature and highlights a gap in land clutter theory.The gap concerns clutter models with weather dependence for incidence angles between 20 and 70 degrees. We update with an improved clutter model the system performance method presented at IGARSS 2016 to estimate the SAR system performance taking into account the weather statistics and the landcover of the target area. The performance statistics obtained with this method allow to estimate the fraction of time (e.g. percentage of a month) in which the SAR system can accomplish the user’s requirement. So far the method has been developed for short vegetation (specifically wheat), as source of clutter, and for bare land and urban area as other target areas. A full clutter model is still under development, but results are presented for the weather dependence of the coherent fraction of the scattered power. Since the azimuth spread of clutter power for GeoSAR can exceed the beam footprint in strong weathe rconditions, we expect improved image quality in these conditions. Two example of the effect of different clutter power probability density function are briefly presente
Geosynchronous synthetic aperture radar : design and applications
Synthetic Aperture Radar (SAR) imaging from geosynchronous orbit has significant potential advantages over conventional low-Earth orbit (LEO) radars, but also challenges to overcome. This thesis investigates both active and passive geosynchronous SAR configurations, presenting their different features and advantages. Following a system design trade-off that involved phase uncertainties, link budget, frequency and integration time, an L band bi-static configuration with 8-hour integration time that reuses the signal from a non-cooperative transmitter has been presented as a suitable solution. Cranfield Space Research Centre looked into this configuration and proposed the GeoSAR concept, an L band bi-static SAR based on the concept by Prati et al. (1998). It flies along a circular ground track orbit, reuses the signal coming from a noncooperative transmitter in GEO and achieves a spatial resolution of about 100 m. The present research contributes to the GeoSAR concept exploring the implications due to the 8-hour integration time and providing insights about its performance and its possible fields of application. Targets such as canopies change their backscattered phase on timescales of seconds due to their motion. On longer time scales, changes in dielectric properties of targets, Earth tides and perturbations in the structure of the atmosphere contribute to generate phase fluctuations in the collected signals. These phenomena bring temporal decorrelation and cause a reduction in SAR coherent integration gain. They have to be compensated for if useful images are to be provided. A SAR azimuth simulator has been developed to study the influence of temporal decorrelation on GeoSAR point spread function. The analysis shows that ionospheric delay is the major source of decorrelation; other effects, such as tropospheric delay and Earth tides, have to be dealt with but appear to be easier to handle. Two different options for GeoSAR interferometry have been discussed. The system is well suited to differential interferometry, due to the short perpendicular baseline induced by the geometry. A GeoSAR has advantages over a Low Earth Orbit (LEO) SAR system to monitor processes with significant variability over daily or shorter timescales (e.g. soil moisture variation). This potential justifies further study of the concept.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Geosynchronous synthetic aperture radar : design and applications
Synthetic Aperture Radar (SAR) imaging from geosynchronous orbit has significant potential advantages over conventional low-Earth orbit (LEO) radars, but also challenges to overcome. This thesis investigates both active and passive geosynchronous SAR configurations, presenting their different features and advantages. Following a system design trade-off that involved phase uncertainties, link budget, frequency and integration time, an L band bi-static configuration with 8-hour integration time that reuses the signal from a non-cooperative transmitter has been presented as a suitable solution. Cranfield Space Research Centre looked into this configuration and proposed the GeoSAR concept, an L band bi-static SAR based on the concept by Prati et al. (1998). It flies along a circular ground track orbit, reuses the signal coming from a noncooperative transmitter in GEO and achieves a spatial resolution of about 100 m. The present research contributes to the GeoSAR concept exploring the implications due to the 8-hour integration time and providing insights about its performance and its possible fields of application. Targets such as canopies change their backscattered phase on timescales of seconds due to their motion. On longer time scales, changes in dielectric properties of targets, Earth tides and perturbations in the structure of the atmosphere contribute to generate phase fluctuations in the collected signals. These phenomena bring temporal decorrelation and cause a reduction in SAR coherent integration gain. They have to be compensated for if useful images are to be provided. A SAR azimuth simulator has been developed to study the influence of temporal decorrelation on GeoSAR point spread function. The analysis shows that ionospheric delay is the major source of decorrelation; other effects, such as tropospheric delay and Earth tides, have to be dealt with but appear to be easier to handle. Two different options for GeoSAR interferometry have been discussed. The system is well suited to differential interferometry, due to the short perpendicular baseline induced by the geometry. A GeoSAR has advantages over a Low Earth Orbit (LEO) SAR system to monitor processes with significant variability over daily or shorter timescales (e.g. soil moisture variation). This potential justifies further study of the concept.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Space Station Systems: a Bibliography with Indexes (Supplement 8)
This bibliography lists 950 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to researchers, designers and managers engaged in Space Station technology development and mission design. Coverage includes documents that define major systems and subsystems related to structures and dynamic control, electronics and power supplies, propulsion, and payload integration. In addition, orbital construction methods, servicing and support requirements, procedures and operations, and missions for the current and future Space Station are included
Abstracts on Radio Direction Finding (1899 - 1995)
The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography).
Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM.
The contents of these files are:
1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format];
2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format];
3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion
Tropospheric scintillation and attenuation on satellite-to-Earth links at Ka and Q band: modeling, validation and experimental applications
Link budget is a crucial step during the design of every communication system. For
this reason it is fundamental to identify and estimate the effects of the atmosphere
on the electromagnetic signal along the path from the source to the sink. Troposphere
represent the bigger source of attenuation and scintillation for signals in the
microwave and upper frequency spectrum. During last years we have participated
in the European Space Agency “AlphaSat Aldo Paraboni” experimental campaigns
to acquire up to date propagation data at two frequencies of interest for future
communication systems. We realized two high performance low-noise receiver located
in Rome, one at Ka and one at Q band (19.701 and 39.402 GHz) to detect the two
signal beacons sent from the AlphaSat geostationary satellite to a wide area over
Europe. Collected data from Rome receiving station have been analysed to measure
excess attenuation and scintillation along the path. Such statistics collected in a
database together with data from other experimenter will be in the near future a
useful instrument, giving professionals updated data for their custom application
design.
Classical link budget techniques rely on climatological atmospheric statistics
based on different time-scales, usually data collected for several years. In the
background of the European Space Agency “STEAM” project, we proposed the use
of high resolution 3D weather forecast models (up to 166m pixel resolution) for the
calculation of excess attenuation and tropospheric scintillation for satellite to earth
link. As a result, the estimation of these electromagnetic parameters to use in link
budgets could be given no more as a statistical analysis of past events as in the
case of Internation Telecommunication Union recommendation but as time-series
forecast specific for the selected receiving station and along the slant path of the
transmitted signal. Case studies for the use of this technique have been deeply
analysed and results compared with data from the AlphaSat measurement campaign
for the Rome and Spino d’Adda receiving station, confirming the validity even in
different geographical regions.
In everyday situations, propagation models based on statistics are often replaced
by the use of easier to apply parametric models. Those have the advantage of
the simplicity and the need of less input parameter to be applied. In particular,
for what concerning the tropospheric scintillation, the Hufnagel-Valley refractive
index structure constant (C2n
) parametric model is actually the most used, due to
the simplicity and the relative accuracy. We here propose a new Cn2 polynomial
parametric model (CPP) based just on the altitude z and a function C2 n0(to,RH0)
that allow to calculate the ground refractive index structure constant just using the
ground temperature (T0) and the relative humidity (RH0). In this work CPP and
Hufnagel-Valley models are applied to different location around the globe to prove
their accuracy. The obtained model could be also used in the future to realize a
simulator able to generate random C2n
vertical profiles specific for the receiver site
Large space structures and systems in the space station era: A bibliography with indexes (supplement 04)
Bibliographies and abstracts are listed for 1211 reports, articles, and other documents introduced into the NASA scientific and technical information system between 1 Jul. and 30 Dec. 1991. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems
Space station systems: A bibliography with indexes (supplement 6)
This bibliography lists 1,133 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1987 and December 31, 1987. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems. The coverage includes documents that define major systems and subsystems, servicing and support requirements, procedures and operations, and missions for the current and future Space Station