| 1. |
- 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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| 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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