| 1. |
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| 2. |
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| 3. |
- Berg, Anders, 1983, et al.
(författare)
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Demonstration of X-Band SAR Interferometry over Baltic Fast Ice
- 2013
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Ingår i: Proceedings of Earth Observation and Cryosphere Science, 13 - 16 November 2012, Frascati, Italy. - 1609-042X. - 9789290922766 ; 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study utilizes X-band SAR images acquired by theCosmo-SkyMed satellite constellation to map fast icedeformation at high spatial resolution. Twointerferometric acquisitions were performed in themiddle of the ice season in 2012 and with a temporalbaseline of 24 hours. The first interferogram revealsdeformation of the fast ice which is being forced by theramming drift ice. The drift ice moved towards the fastice with up to 600 m based on phase correlationmeasurements. The second interferogram shows a ratherlow fringe rate over the fast ice with fringes beingaligned along the coastline. Emerging cracks are easilyidentified with the associated phase discontinuities. It isalso observed that the backscatter and coherence levelsare connected in certain regions.
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| 4. |
- Berg, Anders, 1983, et al.
(författare)
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Evaluation of a sea ice algorithm for SAR data from the Bay of Bothnia
- 2010
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Ingår i: Proceedings of the Third International Workshop SeaSAR 2010, 25-29 January 2010, Frascati, Italy. - 1609-042X. - 9789292212438 ; ESA SP-679
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A sea ice drift algorithm published by M. Thomas et. al.(2008) has been implemented and evaluated. Input tothe algorithm is Synthetic Aperture Radar (SAR)images, which are processed using phase correlation ina multi-resolution processing system. The algorithm hasbeen tested with horizontally co-polarized (HH)ENVISAT ASAR Wide Swath images andRADARSAT-2 ScanSAR images. The possible benefitsof using cross-polarized (HV) RADARSAT-2 ScanSARdata are investigated, and initial testing of the algorithmfor L-band SAR data from ALOS PALSAR has beendone.The validity of the produced motion fields has beentested in three different ways. Most of the SAR imagesin this analysis were acquired over the Bay of Bothnia.Five meteorological stations located in this region havebeen collecting wind data with a temporal resolution ofthree hours. It is confirmed that the wind data correlateswith the derived sea ice motion. Another source ofvalidation data that has been used is the daily ice chartspublished by the Swedish Meteorological andHydrological Institute (SMHI). The third method usedfor validation is straightforward, visual tracking of seaice features.The algorithm is facing some difficulties when it comesto ice tracking close to the shoreline, in archipelagoesetc, since the motionless solution will be favoured. Itcan however be suppressed by filtering areas of land.This addition gives a more robust algorithm.
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| 5. |
- Dischler, Johann, et al.
(författare)
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Predicted properties of eclipsing binaries observable by Gaia
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 569-572
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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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| 6. |
- Dorch, S.B.F., et al.
(författare)
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Dynamo action in M-dwarfs
- 2005
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Ingår i: ESA SP (Special Publication). - 1609-042X .- 0379-6566. ; 560, s. 515-517
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Konferensbidrag (refereegranskat)
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| 7. |
- Dravins, Dainis, et al.
(författare)
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Wavelength shifts in solar-type spectra
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 560, s. 113-119
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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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| 8. |
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| 9. |
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| 10. |
- Fransson, Johan E.S.
(författare)
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Examples of thematic mapping with ERS-Envisat tandem cross-interferometry
- 2010
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Ingår i: ESA SP (CD-ROM). - 1609-042X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper deals with some aspects of thematic mapping using ERS-Envisat Tandem (EET) cross-interferometry (CInSAR). The long baseline of EET CInSAR and the short temporal baseline are in theory suitable for establishing a certain sensitivity of coherence and InSAR phase upon vegetation parameters. Here we show signatures of coherence and InSAR phase for maize fields in Switzerland, and clear-cuts and forest stem volume in Sweden. Both coherence and InSAR phase show sensitivity to vegetation height. By means of the Interferometric Water Cloud Model (IWCM) it is possible to describe the measurements by assuming a weak attenuation and low temporal decorrelation. Clearcuts show higher coherence than mature forests, although strong spatial decorrelation occurs in case of sloped terrain, not correctly accounted for when applying the common-band filter in interferometric processing. Coherence presents a certain sensitivity to stem volume, but only for flat terrain. The IWCM could describe the trend in the measurements reasonably well.
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| 11. |
- Islam, Md. Tariqul, 1980
(författare)
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RIVER CHANNEL MIGRATION: A REMOTE SENSING AND GIS ANALYSIS
- 2010
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Ingår i: Proceedings of ESA Living Planet Symposium. 28 June - 2 July 2010, Bergen, Norway / edited by H. Lacoste-Francis. - 1609-042X. - 9789292212506 ; :SP-686
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Konferensbidrag (refereegranskat)abstract
- Remote sensing and geographic information system provide tools for quantitative and qualitative river morphological analysis. Bangladesh is a riverine, flood prone country and, the Padma and the Jamuna are two of major three rivers in the country. The aim of this research is to monitor the channel migration of the Padma and the Jamuna rivers since 1977 to 2004 using remote sensing and GIS. Four scenes for dry season’s cloud free Landsat images were used in this study. Images were processed using PCI Geomatica and ArcGIS 9.3 was used for GIS analysis. The Landsat images were visualized and identified nine locations to investigate the channel migration. The images were classified into two broad categories, i.e. water and nonwater body. ArcGIS 9.3 was used to transfer these classified images into GIS layers. A standard measurement tool of ArcGIS was applied to measure the movement of river channel based on initial river channel in 1977. General trend of the Padma and the Jamuna river channel migration at locations A, B, C, D, F, G, H and I towards north, northeast and southwest eventually, north, northeast, east, east, west and west, respectively. The confluence point of the Padma and Jamuna (at location E) migrated toward southeast with high rate. During 1977-2004, it migrated about 9000m toward southeast. Trend of migration of the confluence point was faster than any other locations in the channel of the Padma river.
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| 12. |
- Johansson, Anders J
(författare)
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Performance measures of implant antennas
- 2006
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 626 SP
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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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| 13. |
- Jørgensen, Bjarne Rosenkilde, et al.
(författare)
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Determination of star formation histories from gaia-type photometric and astrometric survey data
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566 .- 1609-042X. ; 576, s. 171-173
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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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| 14. |
- Khosravi, Maryam, 1975, et al.
(författare)
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Climatologies of stratospheric short-lived species from Odin/SMR: Methodology for ClO
- 2013
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Ingår i: Proceedings ESA Living Planet Symposium, 9-13 September 2013, Edinburgh (UK). ESA-SP-722 : European Space Agency, Noordwijk, The Netherlands. - 1609-042X. - 9789292212865 ; , s. 1-6
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Sub-Millimetre Radiometer (SMR) on board theOdin satellite has been measuring short-lived strato-spheric species such as chlorine monoxide (ClO) sinceOdin’s launch in 2001. Odin/SMR at its sun-synchronousorbit measures at certain local times observations aroundsunrise and sunset at the equator. Due to the drift ofOdin’s orbit in local solar time and the fact that mea-surements are done at different local times, a correctionis required before a monthly zonal mean climatologycan be calculated and trends of ClO can be evaluated.To deal with this, scaling factors are calculated using aphoto-chemical box model for correction of the mixingratios respective to a reference time. The uncertaintiesand limitations of this method are estimated by checkingthe internal consistency of the results, so that comparingthe scaled a.m. ClO time-series to p.m. scaled time-series should give the same results. We found out thatscaling SMR ClO to the ascending time of MicrowaveLimb Sounder (MLS) as reference at about 1.30 a.m. atthe equator gives better result compared to the scalingClO to MLS descending node at about 1.30. p.m. Thetime series calculated for the morning SMR ClO scaled(to 1.30 a.m.) agrees with the evening ClO scaled.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Lindegren, Lennart
(författare)
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The astrometric instrument of Gaia: Principles
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 29-34
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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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| 19. |
- Ludwig, Hans-Günter, et al.
(författare)
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Status and future of hydrodynamical model atmospheres
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 560, s. 319-325
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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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| 20. |
- Muscheler, Raimund, et al.
(författare)
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Long-term climate variations and solar effects
- 2003
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. - 929092845X ; 535, s. 305-316
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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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| 21. |
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| 22. |
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| 23. |
- Perot, Kristell, 1985, et al.
(författare)
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Odin/SMR Observations of a Particularly Strong Midwinter Stratospheric Sudden Warming in Early 2013
- 2013
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Ingår i: Proceedings of ESA Living Planet Symposium. - 1609-042X. - 9789292212865 ; SP-722
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Sub-Millimetre Radiometer (SMR), on boardthe Odin satellite, observed a major stratospheric suddenwarming (SSW) in the northern hemisphere in earlyJanuary 2013. The provided measurements have beenused to identify and characterize this event which seemsto be the strongest of that kind in recent years. Thispaper is based on a comparison with the 2009 SSWwhich was so far considered as a record-breaking event.SSWs are an important manifestation of the couplingphenomena between the mesosphere / lowerthermosphere and the lower atmospheric layers and canstrongly affect the middle atmospheric composition. It iscrucial to study these events in order to get a betterunderstanding of the dynamical and chemicalmechanisms that control this part of the atmosphere.
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| 24. |
- Plicanic, Vanja, et al.
(författare)
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Antenna diversity evaluation for mobile terminals
- 2006
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566 .- 1609-042X. ; 626 SP
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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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| 25. |
- Sagi, Kazutoshi, 1984, et al.
(författare)
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Twelve years of Arctic ozone loss observed by the Odin satellite
- 2013
-
Ingår i: Proceedings of ESA Living Planet Symposium, SP-722. - 1609-042X. - 9789292212865
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In 2011, several groups reported dramatic ozone depletion over the arctic polar region approaching that of the Antarctic ozone hole. Odin, The Swedish-led satellite project in collaboration with Canada, France and Finland, was launched in February 2001 and continues to produce profiles of chemical species relevant to understanding the middle and upper atmosphere.This study concerns ozone loss over the northern pole utilizing the 12 years of ozone data from Odin/SMR.The unstable nature of the arctic vortex due to the propagation of planetary waves from troposphere makes quantifying chemical ozone loss in the arctic more difficult. The assimilation technique using a transport model is useful for separating the dynamical and chemical changes in the ozone amount as demonstrated earlier by Roseval et al (2007) . We have applied this method with a number of improvements to study the inter-annual variability during the entire Odin period.
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| 26. |
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| 27. |
- Sjöberg, Daniel
(författare)
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An integral equation method dealing with surface waves on large finite periodic structures
- 2006
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566 .- 1609-042X. ; 626 SP
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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.
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| 28. |
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| 29. |
- Svensson, Fredrik, et al.
(författare)
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Hydrodynamical simulations of convection-related stellar micro-variability
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 560, s. 979-984
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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.
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| 30. |
- Söderhjelm, Staffan
(författare)
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Census of binaries - The big picture
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 97-104
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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.
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| 31. |
- Ulander, Lars, 1962, et al.
(författare)
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Borealscat: A tower experiment for understanding temporal changes in P- and L-band backscattering from a Boreal forest
- 2016
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. - 9789292213053 ; 740
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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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| 32. |
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| 33. |
- Urban, Joachim, 1964, et al.
(författare)
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Global observations of stratospheric heavy ozone isotopologue enrichment with the Odin Sub-Millimetre Radiometer
- 2013
-
Ingår i: Proceedings ESA Living Planet Symposium, 9-13 September 2013, Edinburgh (UK). - 1609-042X. - 9789292212865 ; ESA-SP-722
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Odin Sub-Millimetre Radiometer (SMR) measures thermal emission lines of several minor ozone isotopologues such as symmetric and asymmetric O3-18 and asymmetric O3-17 at the atmospheric limb. The global data set spans over 11 years starting in late 2001. The basic characteristics and limitations of the observational data are presented and the global distribution of heavy ozone isotopologue enrichment as seen by Odin is described and discussed. Best results in terms of spatial coverage are obtained for asymmetric O3-18, which shows a characteristic increase of the enrichment in the middle to upper stratosphere and the smallest enrichment in the polar lower stratosphere. Symmetric O3-18 is characterised by a layer of maximum enrichment in the middle stratosphere.
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| 34. |
- Wahlgren, Glenn, et al.
(författare)
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Identifying M supergiants with Gaia
- 2005
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 1609-042X .- 0379-6566. ; 576, s. 619-622
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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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| 35. |
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