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Sökning: L773:0379 6566 OR L773:9789292213053

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1.
  • Blomberg, Erik, 1987, et al. (författare)
  • Simulated biomass retrieval from the spaceborne tomographic Saocom-CS mission at L-band
  • 2016
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. - 9789292213053 ; 740
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents an evaluation of above-ground biomass (ABG) retrieval in boreal forests using simulated tomographic synthetic-aperture radar (SAR) data corresponding to the future SAOCOM-CS (L-band 1.275 GHz) mission. Using forest and radar data from the BioSAR 2008 campaign at the Krycklan test site in northern Sweden the expected performance of SAOCOM-CS is evaluated and compared with the E-SAR airborne Lband SAR (1.300 GHz). It is found that SAOCOM-CS data produce retrievals on par with those obtained with E-SAR, with retrievals having a relative RMSE of 30% or less. This holds true even if the acquisitions are limited to a single polarization, with HH results shown as an example.
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2.
  • Ulander, Lars, 1962, et al. (författare)
  • Borealscat: A tower experiment for understanding temporal changes in P- and L-band backscattering from a Boreal forest
  • 2016
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. - 9789292213053 ; 740
  • Konferensbidrag (refereegranskat)abstract
    • This paper describes the tower-based radar BorealScat, which is being developed for polarimetric, tomographic and Doppler measurements at the hemi-boreal forest test site in Remningstorp, Sweden. The facility consists of a 50-m high tower equipped with an antenna array at the top of the tower, a 20-port vector network analyser (VNA), 20 low-loss cables for interconnection, and a calibration loop with a switching network. The first version of BorealScat will perform the full set of measurements in the frequency range 0.4-1.4 GHz, i.e. P-band and L-band. The tower is currently under construction at a forest stand dominated by Norway spruce (Picea abies (L.) Karst.). The mature stand has an above-ground dry biomass of 300 tons/ha. Data collections are planned to commence in autumn 2016.
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3.
  • Volski, V., et al. (författare)
  • Overview of the software integration activities within ACE
  • 2006
  • Ingår i: First European Conference on Antennas and Propagation (EuCAP), 2006, Nice, France, 6 - 10 November 2006. - : IEEE. - 0379-6566. - 9789290929376 ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • The ACE project initiated the start of several integration activities between European institutions involved in electromagnetic modeling of antennas with planar or conformal topologies. The goal of the integration activities was / is not to create a global software package that integrates the software of all partners, but to initiate a long term process for antenna software integration activities within the European antenna community. During the first two years of ACE the integration activities were performed in several groups with a rather small number of partners in each group. The groups were formed by partners who wanted to integrate a specific approach developed by one partner into the software code of another partner. This allows increasing the capability and efficiency of a software code. In this paper a short overview of all integration activities is given.
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4.
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5.
  • Ban, Yifang, et al. (författare)
  • EO4Urban : First-year results on Sentinel-1A SAR and Sentinel-2A MSI data for global urban services
  • 2016
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 9789292213053
  • Konferensbidrag (refereegranskat)abstract
    • The overall objective of this research is to evaluate multitemporal Sentinel-1A SAR and Sentinel-2A MSI data for global urban services using innovative methods and algorithms, namely KTH-Pavia Urban Extractor, a robust algorithm for urban extent extraction and KTHSEG, a novel object-based classification method for detailed urban land cover mapping. Ten cities around the world in different geographical and environmental conditions were selected as study areas. Large volume of Sentinel-1A SAR and Sentinel-2A MSI data were acquired during vegetation season in 2015 and 2016. The preliminary urban extraction results showed that urban areas and small towns could be well extracted using multitemporal Sentinel-1A SAR data with the KTH-Pavia Urban Extractor. For urban land cover mapping, multitemporal Sentinel-1A SAR data alone yielded an overall classification accuracy of 60% for Stockholm. Sentinel-2A MSI data as well as the fusion of Sentinel-1A SAR and Sentinel-2A MSI data, however, produced much higher classification accuracies, both reached 80%.
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6.
  • Buchwitz, M., et al. (författare)
  • The GHG-CCI project of ESA's climate change initiative : Data products and application
  • 2016
  • Ingår i: Proceedings of Living Planet Symposium 2016. - 9789292213053 ; SP-740
  • Konferensbidrag (refereegranskat)abstract
    • The goal of the GHG-CCI project (http://www.esa-ghg-cci.org/) of ESA's Climate Change Initiative (CCI) is to generate global atmospheric satellite-derived carbon dioxide (CO2) and methane (CH4) data sets as needed to improve our understanding of the regional sources and sinks of these important greenhouse gases (GHG). Here we present an overview about the latest data set called Climate Research Data Package No. 3 (CRDP3). We focus on the GHG-CCI project core data products, which are near-surface-sensitive column-averaged dry air mole fractions of CO2 and CH4, denoted XCO2 (in ppm) and XCH4 (in ppb) retrieved from SCIAMACHY/ENVISAT (2002-2012) and TANSO-FTS/GOSAT (2009-today) nadir mode radiance observations in the near-infrared/shortwave-infrared spectral region. The GHG-CCI products are primarily individual sensor Level 2 products. However, we also generate merged Level 2 products ("EMMA products"). Here we also present a first GHG-CCI Level 3 product, namely XCO2 and XCH4 in Obs4MIPs format (monthly, 5°×5°).
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7.
  • Carlsson, Jan, 1962 (författare)
  • Results and experiences from two years of benchmarking of measurements facilities for small antennas and terminals within ACE
  • 2006
  • Ingår i: European Conference on Antennas and Propagation: EuCAP 2006; Nice; France; 6 November 2006 through 10 November 2006. - : IEEE. - 0379-6566. - 9789290929376 ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents the test cases defined in ACE (European Antenna Centre of Excellence) for benchmarking of facilities for measuring small mobile terminals and antennas, as well as results and experiences of the round robin test. The emphasis is put on measurements in the most popular communication frequency bands. Several test cases for passive antennas as well as for active devices were defined and collected in a test kit that was sent to different test facilities around Europe in a round robin test. The measured parameters include radiation efficiency, total radiated power, diversity gain and receiver sensitivity. The test cases include different locations of the test devices relative to a lossy cylinder that has dielectric characteristics resembling that of a human head.
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8.
  • Cordoba-Jabonero, Carmen, et al. (författare)
  • Assessments for possible habitability in Martian polar environments : Fundaments based in ice screening of UV radiation
  • 2004
  • Ingår i: ESA SP. - 0379-6566 .- 1609-0438. ; 545, s. 187-188
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a study of the solar UV radiation in Martian high latitude environments covered by ice, where the UV propagation through the polar cover depends on the ice radiative properties (layers of H2O or CO 2 ice). But also we will investigate the changes in the subsurface UV levels induced by the seasonal variations of solar UV flux on the surface, as well as by the seasonal freezing-thawing and related CO2 sublimation processes. The biological dose relative to DNA-damage will be also estimated for biological implication assessments. All these studies will be compared with the biological dose received in the Antarctic snow-ice covered environment which is seasonally exposed to high UV radiation levels (formation of "ozone hole"), where the environmental conditions could be similar to those present on Mars
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9.
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10.
  • Diallo, A., et al. (författare)
  • Reverberation chamber evaluation of multi-antenna handset having low mutual coupling and high efficiencies
  • 2006
  • Ingår i: European Conference on Antennas and Propagation: EuCAP 2006; Nice; France; 6 November 2006 through 10 November 2006. - 0379-6566. - 9789290929376 ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents the evaluation of the diversity performances of several multi-antenna structures in a reverberation chamber. Firstly, a two-antenna system having low isolation between the radiators is measured. Its performances are compared with a second structure which uses a neutralization technique to enhance the radiating element's isolation. Then the performances of a four-antenna system with and without the neutralization method are measured and presented. Particularly, the total antenna efficiencies, the envelope correlation coefficients and the diversity gain of these systems are presented and discussed. We especially focus on the advantages of the neutralization technique.
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11.
  • Dischler, Johann, et al. (författare)
  • Predicted properties of eclipsing binaries observable by Gaia
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 569-572
  • Konferensbidrag (refereegranskat)abstract
    • Using a population synthesis model we estimate the fraction of stars of different types that are likely to show eclipses, as a function of the period. The population model is based on the bse-code from Hurley et al. (2002) which is a rapid binary evolution code that include all common effects in close binaries such as mass transfer, tidal locking, wind etc. We use this to evolve millions of systems from original distributions in separation, mass and eccentricity, with ages between zero and 12 Gyr, to get a population of systems representative of our Galaxy. The binary data from our model are then analysed in order to, statistically, see how many eclipsing systems we should have. This is done with a simple model where we neglect limb-darkening and other complicating effects. Assuming a random distribution of the inclination angle the probability of an eclipse of a given depth, Am, can easily be calculated. Adding a reasonable fraction of true single stars, we can finally estimate the fraction of eclipsing binaries in limited areas of the HR-diagram, as a function of the period. A first comparison with observational data from the Hipparcos mission shows quite satisfying agreement, and extrapolation to Gaia should thus be a natural application. We find that Gaia will observe about 500 000 eclipsing binaries, this (surprisingly) small number arises from the fact that many eclipsing systems will not be detected by Gaia.
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12.
  • Dorch, S.B.F., et al. (författare)
  • Dynamo action in M-dwarfs
  • 2005
  • Ingår i: ESA SP (Special Publication). - 1609-042X .- 0379-6566. ; 560, s. 515-517
  • Konferensbidrag (refereegranskat)
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13.
  • Dravins, Dainis, et al. (författare)
  • Wavelength shifts in solar-type spectra
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 560, s. 113-119
  • Konferensbidrag (refereegranskat)abstract
    • Spectral-line displacements away from the wavelengths naively expected from the Doppler shift caused by stellar radial motion may originate as convective shifts (correlated velocity and brightness patterns in the photosphere), as gravitational redshifts, or perhaps be induced by wave motions. Absolute lineshifts, in the past studied only for the Sun, are now accessible also for other stars thanks to astrometric determination of stellar radial motion, and spectrometers with accurate wavelength calibration. Comparisons between spectroscopic apparent radial velocities and astrometrically determined radial motions reveal greater spectral blueshifts in F-type stars than in the Sun (as theoretically expected from their more vigorous convection), further increasing in A-type stars (possibly due to atmospheric shockwaves). Work is in progress to survey the spectra of the Sun and several solar-type stars for "unblended" photospheric lines of most atomic species with accurate laboratory wavelengths available. One aim is to understand the ultimate information content of stellar spectra, and in what detail it will be feasible to verify models of stellar atmospheric hydrodynamics. These may predict bisectors and shifts for widely different classes of lines, but there will not result any comparison with observations if such lines do not exist in real spectra, or are too blended for meaningful measurement. An important near-future development to enable a further analysis of stellar surface structure will be the study of wavelength variations across spatially resolved stellar disks, e.g., the center-to-limb wavelength changes along a stellar diameter, and their spatially resolved time variability.
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14.
  • Eklundh, Lars, et al. (författare)
  • High resolution mapping of vegetation dynamics from Sentinel-2
  • 2012
  • Ingår i: Proceedings of 1st Sentinel-2 Preparatory Symposium. - 0379-6566. - 9789290922711 ; 707 SP
  • Konferensbidrag (refereegranskat)abstract
    • The aim of this work is to develop and test a method for generation of information on vegetation dynamics from high-spatial resolution data, such as Sentinel-2. In order to accomplish this, Sentinel-2 data were simulated from existing SPOT HRG and HRVIR scenes over Sweden. We used TIMESAT, a well-tested computer package for generating smooth seasonal profiles and generation of seasonality parameters, like start and end, length, amplitude, integrated values, seasonal maximum, derivatives, etc. The processing works on a pixel-by-pixel basis and is resistant to clouds and noise. Data gaps are handled, and quality information can be included to increase the fidelity of the fits. The pilot study demonstrated that TIMESAT was successful in fitting smooth model functions to the data, and generating seasonality parameters for the test area at 10 × 10 m resolution. We conclude that TIMESAT will be useful for generating vegetation dynamics data from high-spatial resolution data such as Sentinel-2. The smooth seasonal profiles will be extremely useful for driving high-resolution biophysical vegetation models, and the seasonality parameters will be excellent for change detection, and for studying trends in vegetation productivity and seasonality.
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15.
  • Escoubet, C. P., et al. (författare)
  • Imaging the magnetosphere using ISEE-1 spacecraft potential
  • 1996
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :392, s. 179-187
  • Tidskriftsartikel (refereegranskat)abstract
    • The potential of ISEE 1 spacecraft has been used to derived the plasma density in the magnetosphere and its environment. First we show that using the equilibrium of currents flowing in and out of a spacecraft, we could derive numerically a relation between the spacecraft potential and the density of the surrounding plasma. After verifying that this relation was in good agreement with the measurement of the density made by other instruments during selected periods of time, we apply this relation to the spacecraft potential measured continuously from 1977 to 1984 on ISEE-1. An image of the plasma density in the magnetosphere and its environment is obtained as a result. All principal magnetospheric regions are clearly identified, from the solar wind with a density around 5 cm-3 , the magnetosheath around 50 cm-3, the magnetosphere around 1 cm-3, the plasma sheet around 0.5 cm-3 and finally the more tenuous tail lobes below 0.1 cm-3. The plasma density was observed slightly higher on the dawnside than on the dusk side of the magnetosphere. In addition the magnetosheath was closer to the Earth on the dawnside than on the duskside. When the magnetic activity increased (recorded by the AE index), the dayside magnetosphere was compressed/eroded by about 1 to 2 RE while the plasmasphere/inner magnetosphere became quite irregular and expanded in the dawn-midnight and in the dusk-noon sectors. In addition, during high magnetic activity, the plasmasheet at Ygsm = 0 was thicker and denser than at low activity. On the other hand the flanks of the plasmasheet were thinner and less dense during high activity than during low activity.
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16.
  • Fecht, H. -J, et al. (författare)
  • Thermophysical properties of liquids : Modelling and non-metallic materials
  • 2005
  • Ingår i: ESA SP. - 0379-6566 .- 1609-0438. ; :1281, s. 24-35
  • Tidskriftsartikel (refereegranskat)abstract
    • The accurate knowledge and high-precision measurements of the thermophysical properties of liquids is necessary for the numerical modeling of industrial processes where the solid-liquid phase transformation plays a crucial role. The reduction of magnetic levitation forces in microgravity leads either to a significant improvement in accuracy or makes the measurement possible in the first place. High-precision measurements on chemically highly reactive melts require containerless processing using non-contact diagnostic tools. Scientific precursor experiments were conducted in the TEMPUS containerless processing facility during the Spacelab IML-2 and MSL-1 missions, also.
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17.
  • Feldstein, Yakov I., et al. (författare)
  • To directly driven and loading-unloading processes during substorm
  • 1996
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :389, s. 69-74
  • Tidskriftsartikel (refereegranskat)abstract
    • Model calculations of the electric fields in the high-latitude ionosphere are compared to measurements made by the Viking satellite during August 3, 1986 pass. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field (IMF). The event chosen correspond to the growth phase of substorm. The correlation between the model results and the satellite data is high, which assumes directly driven of the magnetosphere by the solar wind. Similar high correlation exists between the electric field in the solar wind (V*Bs) and AL magnetic activity indices, if time delays between the V*Bs observations in space and magnetic activity above the Earth's ground are taken into account. It is concluded, that the directly driven response of the magnetosphere to highly variable solar wind electric field is the main feature of geomagnetic activity at high latitudes.
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18.
  • Feldt, Robert, et al. (författare)
  • Analyzing the cost of complying to the ECSS standards for software development
  • 2010
  • Ingår i: European Space Agency, (Special Publication) ESA SP. Conference on DAta Systems in Aerospace, DASIA 2010; Budapest; 1-4 June 2010. - Budapest : European Space Agency. - 0379-6566. - 9789290922469 ; 682, s. 303-307
  • Konferensbidrag (refereegranskat)abstract
    • Software for space applications has special requirements in terms of reliability and dependability. Standards are one of the primary mechanisms to ensure a sufficient quality level, with the European Cooperation on Space Standardization (ECSS) standards being the main ones. The use of standards is not only a benefit since they can incur considerable costs in terms of, for example, additional documentation and activities. For making the right decisions on which development and quality assurance activities to focus on it is important to know not only their added value but also their costs. Here we present a method for analyzing the cost of standard compliance (CoSC) in software development. It is based on a model which divides the costs into four different types based on their primary value: development, quality-adding, confidence-adding and adherence. The adherence costs are those costs that are incurred by or follows from the use of a standard but does not add any immediate value to either the functionality, quality or quality assurance of the software. Initial results from applying the method in an industrial company adhering to ECSS is presented.
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19.
  • Feldt, Robert, et al. (författare)
  • Optimizing Verification and Validation Activities for Software in the Space Industry
  • 2010
  • Ingår i: European Space Agency, (Special Publication) ESA SP. Conference on DAta Systems in Aerospace, DASIA 2010; Budapest; 1-4 June 2010. - Budapest : European Space Agency. - 0379-6566. - 9789290922469 ; , s. 309-313
  • Konferensbidrag (refereegranskat)abstract
    • Software for space applications has special requirements in terms of reliability and dependability and the verification & validation activities (VAs) of these systems often account for more than 50% of the develop- ment effort. The industry is also faced with political and market pressure to deliver software faster and cheaper. Thus new ways are needed to optimize these activities so that high quality can be retained even with reduced costs and effort. Here we present a framework for the management and optimization of verification & validation activities (VAMOS). An initial evaluation of the framework based on historical data as well as data extracted with a new tool has been done and are described briefly.
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20.
  • Johansson, Anders J (författare)
  • Performance measures of implant antennas
  • 2006
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • Modern electronic medical implants have reached a high degree of complexity. This has increased the demands on the communication link with the implant, both regarding the bandwidth and the communication distance. A medical communication system at RF frequencies has been standardised, the Medical Implant Communication System (MICS), which use a frequency allocation of 402 - 405 MHz. This frequency band is allocated for implant use both and the US and in the EU. The EIRP is limited to -16 dBm in order to reduce the interference to existing users of the same frequency band. This low EIRP makes it necessary to have reasonable effective antennas in the implants in order to get a benefit form the switch from the classical inductive link to RF. The normal performance measures of antennas have to be modified when applied to implant antennas. The reflection coefficient S11 and the VSWR are straightforward to use also in the implant case. But the gain definition is only valid in a lossless medium. This is not a problem for the implanted antenna, as it is placed in a finite body, i.e. the patient. The implant and the body carrying it will act as one larger antenna, and will have a measurable gain according to the classic definition. The drawback is that the gain will depend heavily on the size and shape of the body, which makes it hard to give a generic value for the gain from a certain antenna. The type of antenna and the amount of isolation around the antenna will influence the amount of nearfield losses, and thus the efficiency. There is a modification of the efficiency measure which solves the problem of the gain definition in an infinite lossy medium [the]. This efficiency measure is a candidate for a quality measure of implanted antennas. The efficiency of an antenna in an infinite lossy material is evaluated by calculating the integral of the Poynting vector over a closed surface in the far zone of the antenna.
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21.
  • Jørgensen, Bjarne Rosenkilde, et al. (författare)
  • Determination of star formation histories from gaia-type photometric and astrometric survey data
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566 .- 1609-042X. ; 576, s. 171-173
  • Konferensbidrag (refereegranskat)abstract
    • To understand the evolution of the Milky Way Galaxy requires detailed knowledge of the star formation history of various populations. The vast amounts of photometric and astrometric data provided by the Gaia mission give unprecedented opportunities in this area. The relationships between the observed data and the ages of stars are however complex and highly non-linear and great care must be taken in analyzing the data. We describe a Bayesian approach to calculate the star formation rate (SFR) from astrophysical data, using a genetic algorithm to solve the basic integral equation. We present simulations showing that the method is capable of resolving structures in the SFR that cannot be seen from a distribution of the individually estimated stellar ages.
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22.
  • Karlsson, Kristian, 1973, et al. (författare)
  • Analysis of Wires Inside a Reverberation Chamber Using the Method of Moments Combined with Spectral Domain Techniques and Asymptotic Extraction
  • 2006
  • Ingår i: European Conference on Antennas and Propagation: EuCAP 2006; Nice; France; 6 November 2006 through 10 November 2006. - : IEEE. - 0379-6566. - 9290929375 ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we will present a Method of Moments (MoM) code that can be used for analyzing PEC objects in a Reverberation Chamber (RC). The RC is treated as a rectangular cavity, and the Green's function of it is constructed by using planar wave spectral domain techniques and imaging combined with periodic boundary conditions. Several validation cases based on comparisons with other computer codes are also presented.
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23.
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25.
  • Lindegren, Lennart (författare)
  • The astrometric instrument of Gaia: Principles
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 29-34
  • Konferensbidrag (refereegranskat)abstract
    • Compared with Hipparcos, Gaia will give an enormous improvement in accuracy, completeness and number of stars: about two orders of magnitude in accuracy, four orders in number, and a completeness limit that is 12 magnitudes fainter. How is all this possible? The answer is: by a combination of many factors, the most important being bigger and more efficient detectors, and bigger optics. The method of astrometric measurements by Gaia is described from first principles, and the fundamental limitations explained in terms of physics (diffraction and photon noise), geometry, temporal sampling and reference frames. Although Gaia is basically a self-calibrating instrument, things have to be stable enough over time scales that are long enough for the calibrations to be carried out, and the corresponding requirements are outlined. To achieve microarcsecond accuracy is technically extremely demanding, but feasible with a clever and careful design of the instrument.
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26.
  • Ludwig, Hans-Günter, et al. (författare)
  • Status and future of hydrodynamical model atmospheres
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 560, s. 319-325
  • Konferensbidrag (refereegranskat)abstract
    • Since about 25 years ago work has been dedicated to the development of hydrodynamical model atmospheres for cool stars (of A to T spectral type). Despite their obviously sounder physical foundation in comparison with standard hydrostatic models, their general application has been rather limited. In order to understand why this is, and how to progress, we review the present status of hydrodynamical modelling of cool star atmospheres. The development efforts were and are motivated by the theoretical interest of understanding the dynamical processes operating in stellar atmospheres. To show the observational impact, we discuss examples in the fields of spectroscopy and stellar structure where hydrodynamical modelling provided results on a level qualitatively beyond standard models. We stress present modelling challenges, and highlight presently possible and future observations that would be particularly valuable in the interplay between model validation and interpretation of observables, to eventually widen the usage of hydrodynamical model atmospheres within the astronomical community.
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27.
  • Marklund, Göran, et al. (författare)
  • Astrid 2, A low-budget microsatellite mission for auroral research
  • 1997
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :397, s. 387-394
  • Tidskriftsartikel (refereegranskat)abstract
    • The next in the Astrid series of low-budget microsatellite missions will be devoted to classical auroral research. The challenge of this mission is to demonstrate the possibility to carry out comprehensive auroral investigations on a microsatellite platform having the size 0.45 × 0.45 × 0.3 m at a cost of about 2 MUSD. A successful mission will open up new less expensive ways carrying out auroral research in the future, ways which are complementary to the more ambitious programmes run within ESA and NASA. Of particular interest are multipoint measurements within the auroral acceleration region using clusters of microsatellites. New light-weight and compact instruments and deployment systems have been developed for the Astrid-2 mission. The payload will carry an integrated electric and magnetic field instrument, including a Langmuir probe, a lightweight ion and electron spectrometer, and two spin-scanning UV photometers for Lyman α and oxygen emissions in the aurora. The electric field probes will be deployed using a newly developed light-weight system for wire boom deployment. Other novel features to be used on Astrid-2 are data compression and data filtering. Astrid-2 is to be launched on a Kosmos vehicle from Plesetsk in 1997 into an 83° inclination circular orbit at 1000 km altitude. The mission will use a geographically distributed ground station network for high-speed S-band data reception, one station to be located at Solna, Sweden and another at the South African Antarctic base SANAE.
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28.
  • McCutchan, Marvin, et al. (författare)
  • Multitemporal Sentinel-1A data for urban land cover mapping using deep learning : Preliminary results
  • 2016
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - : European Space Agency. - 9789292213053
  • Konferensbidrag (refereegranskat)abstract
    • The objective of this research is to evaluate multitemporal Sentinel-1A SAR data for urban land cover mapping using a pixel-based Deep Belief Network (DBN) and an object-based post-processing. Multitemporal Sentinel-1A SAR in both ascending and descending orbits were acquired in Stockholm during the 2015 vegetation season. The images were first terrain corrected, co-registered, speckle filtered and scaled to 8 bit. Then the images were segmented using KTH-SEG, an edgeaware region growing and merging algorithm. For classification, a pixel-based deep belief network (DBN) was used. Then classification result was post-processed using object-based majority voting. For comparison, the same dataset was classified using an object-based support vector machine (SVM). The preliminary results show that the hybrid deep learning classification scheme produced comparable results as object-based SVM while yielded higher accuracies for builtup classes.
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29.
  • Muscheler, Raimund, et al. (författare)
  • Long-term climate variations and solar effects
  • 2003
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. - 929092845X ; 535, s. 305-316
  • Konferensbidrag (refereegranskat)abstract
    • The cosmogenic radionuclides 14C, 10Be and 36Cl allow us to trace solar variability several tens of millennia back in time. Different methods of reconstructing past solar variability based on radionuclide concentrations measured in ice cores will be discussed. The similarity in the variability of measurements of solar magnetic activity and solar irradiance over the last 20 years makes cosmogenic radionuclides a promising tool for reconstructing the variability of solar irradiance in the past. The analysis of many well-dated, high-resolution climate records and comparison with radionuclide records clearly indicates that solar forcing plays an important role in climate change. However, the underlying mechanisms are still a matter of debate and the climate records do not yet show a conclusive picture.
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30.
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31.
  • Pathan, Risat, 1979, et al. (författare)
  • Temporal Partitioning on Multicore Platform
  • 2014
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. - 9789292212896 ; SP 725
  • Konferensbidrag (refereegranskat)abstract
    • This paper addresses the problem of ensuring temporal partitioning according to the ARINC-653 standard for integrating multiple applications on the same multicore platform. To employ temporal partitioning, we propose the design and analysis of a hierarchical scheduling framework (HSF) for multicore platform. In HSF, each application has a server task, which is mapped to one of the physical cores of the multicore platform. The HSF framework is based on scheduling at two-levels: (i) a system-level scheduler for each core schedules the server tasks that are mapped to that core, and (ii) a task-level scheduler for each application schedules the tasks of the application. This paper presents the design and analysis of this two-level HSF that can be used to ensure temporal partitioning and meeting all the deadlines of each application tasks. The effectiveness of our technique is demonstrated using real-world space applications provided by RUAG Space Sweden AB.
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32.
  • Persson, Henrik, et al. (författare)
  • Estimation of forest variables using radargrammetry on TerraSAR-X data in combination with a high resolution DEM
  • 2013
  • Ingår i: Esa Sp. - 0379-6566. ; 2013
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • This study uses the backscattered intensity information from SAR images acquired with TerraSAR-X to derive Digital Surface Models with radargrammetry. Then the known ground elevation (from airborne lidar) is subtracted to get Canopy Height Models that are analysed and linked through regression analysis to the forest variables above-ground biomass and tree height. It was found, that the used constellation of image pairs and prediction models produced biomass estimations at stand level with 25.9% and 33.8% relative RMSE, while the height estimations were 11.5% and 12.3%. The analyses were tested at the Swedish test sites Krycklan and Remningstorp.
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33.
  • Plicanic, Vanja, et al. (författare)
  • Antenna diversity evaluation for mobile terminals
  • 2006
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566 .- 1609-042X. ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we are focusing on the practical, engineering way of evaluating and characterizing the multi-channel antenna solutions on the mobile terminal. Two methods of calculating the parameters, describing the diversity performance, are described and the practical use of the methods in simulations and measurements are presented and evaluated. The time saving aspect of using the scattering parameters is lifted forward but also its limitations. For comparison, a statistical method for calculating Diversity Gain is also presented. This evaluation is performed for two multi-channel antenna solutions with different characteristics for the purpose of characterizing different diversity performances.
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34.
  • Popielawska, B., et al. (författare)
  • An imprint of the quiet plasma sheet structure at the orbit of viking : Magnetosphere without substorms
  • 1996
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :389, s. 133-139
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a study of the plasma sheet structure as seen on VIKING during prolonged periods of magnetic quiescence. The ion and electron spectrograms, the electric field data and field-aligned current signatures in the magnetic field data are examined. A special attention is paid to cases when the Low Latitude Boundary Layer-like plasma is seen deep in the nightside at latitudes which apparently map to close geocentric distances as it implies an exotic plasma circulation in the tail. An attempt has been made to infer from VIKING data how the quiet plasma sheet is formed, whether it originates mainly from the mantle source via the interaction with the distant tail current sheet or whether the lateral transport of the Low Latitude Boundary Layer (LLBL) from the tail flanks (with essentially adiabatic particle motion) takes place followed by the sunward convection in the central part of the near-Earth tail. The VIKING plasma and electric field data suggest that the last mechanism is decisive for plasma sheet structuring during prolonged periods of northward IMF.
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35.
  • Rothwell, P.L., et al. (författare)
  • Inertial currents and substorm onsets
  • 1996
  • Ingår i: European Space Agency, (Special Publication) ESA SP-389. - 0379-6566. ; , s. 447-452
  • Tidskriftsartikel (refereegranskat)abstract
    • When magnetic field lines are sufficiently stretched during the substorm growth phase, in the equatorial plane the earthward ExB ion drift velocity can become comparable to the ion gyration velocity. Under these conditions inertial currents can become quite important. Using a two-dimensional model we find that O+ ions injected from the ionosphere into the equatorial plane at high latitudes will drift eastward at radial distances less than -10 RE because the inertial drift dominates and westward at distances closer to the earth because the magnetic gradient drift dominates. The inertial eastward drift gives rise to a current which in terms of JxB is consistent with the convective deceleration of the earthward drift velocity due to higher values of B. Similarly, momentum balance requires that the convective acceleration of the westward drift velocity should be consistent with a tailward inertial current. Therefore, an equatorial current wedge system with eastward and tailward current components naturally arises from the ion dynamics. In a future paper a three-dimensional treatment will determine whether curvature drift masks the eastward inertial drift of the oxygen ions.
  •  
36.
  • Sjöberg, Daniel (författare)
  • An integral equation method dealing with surface waves on large finite periodic structures
  • 2006
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566 .- 1609-042X. ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • We present a method for studying large finite periodic structures using software developed for infinite periodic structures. The method is based on the Floquet-Bloch transformation, which splits the spatial description into one microscopic spatial variable inside the unit cell, and one macroscopic wave vector describing the variations on a scale encompassing many unit cells. The resulting algorithm is iterative, and solves an infinite periodic problem in each step, where the sources have been filtered through a windowing function. The computational cost for the iterations is negligible compared to computing the impedance matrices for the infinite periodic problems, and it is shown that the algorithm converges if the periodic structure is large enough.
  •  
37.
  • Sotoudeh, Omid, 1978, et al. (författare)
  • Multimode hard horn antennas with partly corrugated walls for 20/30 GHz dual-reflector antennas with multiple beams - full 3D simulations and measurements
  • 2006
  • Ingår i: European Conference on Antennas and Propagation: EuCAP 2006; Nice; France; 6 November 2006 through 10 November 2006. - 0379-6566. - 9290929375 ; 626 SP
  • Konferensbidrag (refereegranskat)abstract
    • We introduce a partly corrugated hard horn, consisting of a smooth-walled horn with an attached longitudinally corrugated outer section. This is used and controlled to design better and shorter single-band horns than otherwise possible. Furthermore, it enables the design of dual-band horns with low cross-polarization and high gain, for multi function use at Ka-band with transmit and receive frequencies in the same antenna. A model of such a dual-band horn was manufactured at Saab Ericsson Space and measured. The design was done by using efficient in-house mode matching code based on homogenized asymptotic boundary conditions for the corrugations. This has been verified by heavy computations using a 3-D FDTD code. The measured laboratory model had too large cross polar sidelobes, but the later extensive computations showed that these sidelobes would have been in agreement with the mode matching results if the number of corrugations was doubled.
  •  
38.
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39.
  • Svensson, Fredrik, et al. (författare)
  • Hydrodynamical simulations of convection-related stellar micro-variability
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 560, s. 979-984
  • Konferensbidrag (refereegranskat)abstract
    • We used a series of CO5BOLD hydrodynamical model atmospheres covering stellar objects from white dwarfs to red giants to derive theoretical estimates of the photometric and photocentric stellar variability in wavelength-integrated light across the Hertzsprung-Russell diagram. We validated our models against solar measurements from the SoHO/VIRGO instrument. Within our set of models we find a systematic increase of the photometric as well as photocentric variability - which turn out to be closely connected - with decreasing surface gravity. The estimated absolute levels of the photocentric variability do not affect astrometric observations on a precision level expected to be achieved by the GAIA mission - with the exception of close-by giants. The case of supergiants remains to be investigated. In view of the ongoing debate about the photometric non-detection of p-modes in Procyon by the Canadian MOST satellite we remark that we obtain a factor of approximately equals 3 in amplitude between the granular background "noise" in the Sun and Procyon. This statement refers to a particular representation of temporal power spectra as discussed in Sect. 5.
  •  
40.
  • Söderhjelm, Staffan (författare)
  • Census of binaries - The big picture
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 97-104
  • Konferensbidrag (refereegranskat)abstract
    • Gaia will observe huge numbers of binaries with a large range of periods. The present contribution tries to present some estimates of the expected number of detections and/or orbit determinations, based on simplified but large-scale simulations. The simulations have to model both a Galaxy with binaries, the instrument and observations, and the reduction programs. As in previous studies, there are marked distance-effects, with the solar neighbourhood (within a few hundred pc) much more completely sampled than more typical (few kpc) Gaia distances. The large number of simulated solutions allows also a study of some systematic effects in the astrometry of undetected binaries.
  •  
41.
  • Urban, Joachim, 1964, et al. (författare)
  • Odin/SMR Limb Observations of Nitric Acid in the Stratosphere
  • 2007
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; ESA-SP-636:SP-636
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched in February 2001, observes thermal emissions of stratospheric nitric acid (HNO3) originating from the Earth limb in a band centred at 544.6GHz. The characteristics of the retrieved Odin/SMR version-2.0 HNO3 profiles are described. A climatology over more than five years of HNO 3 observations from 2001 to 2007 was created. Different aspects of the data, such as the global distribution and seasonal variation, the denitrification inside the polar vortices as well as the presence of high quantities of HNO3 in the middle and upper stratosphere at midwinter high latitudes are discussed.
  •  
42.
  • Wahlgren, Glenn, et al. (författare)
  • Identifying M supergiants with Gaia
  • 2005
  • Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 619-622
  • Konferensbidrag (refereegranskat)abstract
    • As a group of stars having high luminosity and thus being able to be detected to great distances, massive M supergiants are extremely helpful to the study of the kinematics of the Milky Way. They are also partly responsible for the creation of post iron-group elements through the weak s-process of nucleosynthesis. As there are relatively few classified M supergiants, owing to their rapid pace of evolution, the identification of additional such stars will serve to significantly increase the sample that can be studied, which offers the promise of a higher fidelity in charting the regions of recent star formation in our Galaxy as well as a fuller description of trends that may be detected amongst their chemical compositions. We discuss the identification of M supergiants using the instrumentation onboard the Gaia satellite, emphasizing the nature of the photometric system that will best serve to classify M stars.
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43.
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