363 research outputs found
A Polarimetric Phased Array Antenna for E-SAR in L-Band
The design of a new L-band antenna for DLRâs airborne synthetic aperture radar system (E-/F-SAR) is presented. Beside operations in L-band new components for a system upgrade were developed. These components are intro-duced. Special interest of this paper is the development of the dual-polarized L-Band antenna with enhanced bandwidth of 150MHz. The antenna feed network is equipped with 2bit hybrid phase shifters to steer the beam between 25° and 40° in elevation. For mounting the antenna at the fuselage of a Dornier Do 228-212 aircraft a rack is described to house several antenna configuration
River Run Off Measurement With SAR Along Track Interferometry
The paper summarizes the need for global space borne river run-off measurements. It reports about an airborne SAR experiment aimed to measure the surface velocity of the river Isar in Bavaria / Germany. The results from two different SAR techniques, including Along Track Interferometry (ATI) show good correspondence. Finally suggestions for further studies are given
Depth profile analyses by femtosecond laser ablation (multicollector) inductively coupled plasma mass spectrometry for resolving chemical and isotopic gradients in minerals
Femtosecond laser ablation (fs-LA) coupled to a multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) instrument has been proven to be a powerful means to analyze isotope ratios of ânon-traditionalâ stable isotope systems with high spatial resolution, precision, and accuracy. The technique has been successfully applied, e.g., to investigate diffusion-generated isotopic zoning of the elements Li, Mg, and Fe in magmatic crystals. Here, we present a novel sampling technique employing a fs-LA system that is equipped with a computer numerical control (CNC) laser stage, using the open-source software LinuxCNC. Combining this laser set up with ICP-MS or MC-ICP-MS allows us to perform depth profile analyses of major and trace elements, respectively, as well as metal stable isotope variations of Fe and Mg in olivine crystals and in experimental diffusion couples. Samples are ablated in circular patterns with profile diameters of 100â200â”m using a laser spot size of 25â30â”m. Depending on the scan speed and the repetition rate of the laser, each ablated sample layer is between 300ânm and 3.0â”m thick. The integrated signal of one ablated layer represents one data point of the depth profile. We have tested this technique by analyzing 5â50â”m deep depth profiles (consisting of 15â25 individual layers) of homogeneous and chemically zoned olivine crystal cuboids. The minor and trace element analyses of the zoned cuboids, conducted by fs-LA-ICP-MS, were compared with âhorizontalâ profiles analyzed in polished sections of the cuboids with electron probe microanalysis (EPMA). Furthermore, we analyzed FeâMg isotopic depth profiles of the same cuboids with fs-LA-MC-ICP-MS, of which the chemically zoned ones also showed isotopic zoning at identical scales. Isotopic depth profiles were also conducted on an unzoned olivine cuboid that was coated with a 26Mg- and 56Fe-enriched olivine thin film (of âŒâ800ânm) in order to investigate top-to-bottom contamination during depth profiling. Our results indicate that (i) concentration data acquired by fs-LA depth profiling match well with EPMA data, (ii) precise and accurate Fe and Mg isotopic data can be obtained (i.e., precision and accuracy are â€â0.12ââ° and â€â0.15ââ° for both ÎŽ26Mg and ÎŽ56Fe, respectively), and (iii) potential top-to-bottom contamination during depth profiling of isotope ratios can be avoided. The technique presented herein is particularly suitable for the investigation of minerals or glasses with chemical and/or isotopic gradients (e.g., diffusion zoning) vertical to planar surfaces. It can also be applied in materials sciences in order to analyze thin films, coatings, or surface contaminations on solids
Nouvelles dĂ©couvertes de Lycopodes aplatis (Diphasiastrum) dans lâOdenwald de Hesse
In den Jahren 2003 und 2004 gelangen Nachweise mehrerer FlachbÀrlapp-
Arten (Diphasiastrum) im hessischen Odenwald bei Beerfelden und Olfen. Von
herausragender Bedeutung ist der Fund von D. oellgaardii, welches seit rund 50 Jahren
in Hessen als erloschen galt. Daneben wurden D. complanatum und D. tristachyum an je
einer LokalitÀt neu entdeckt. Die Diphasiastrum-Arten besiedeln an den Wuchsorten bei
Beerfelden und Olfen anthropogene SekundĂ€rstandorte (Skipiste oder StraĂenböschung).
Syntaxonomisch lassen sich die BestÀnde innerhalb der Ordnung Ulicetalia minoris zum
Genisto pilosae-Callunetum oder zu einer Deschampsia-flexuosa-Vaccinium-myrtillus-
Gesellschaft stellen. An beiden Wuchsorten wachsen die FlachbÀrlappe auf stark sauren,
mĂ€Ăig frischen, sandigen Lehmböden. Die Wuchsorte erhalten volle Freilandhelligkeit
oder sind mĂ€Ăig beschattet. Neben populationsbiologischen Parametern wie Anzahl der
Sprosse und FertilitÀt werden Daten zur GefÀhrdung der BestÀnde genannt. Eine Neueinstufung
fĂŒr zwei der drei beobachteten Diphasiastrum-Arten in der Roten Liste fĂŒr Hessen
wird vorgeschlagen.Between 2003 and 2004 new records of several Diphasiastrum species in the
Hesse Odenwald region near Beerfelden and Olfen were made. Especially important is
the record of D. oellgaardii which was assumed to be extinct in Hesse since 50 years.
Beside this, D. complanatum and D. tristachyum were recorded at one new site each.
The growing sites near Beerfelden and Olfen are secondary habitats of anthropogeneous
origin (a skiing track and a road slope). The respective plant communities belong to the
order Ulicetalia minoris (Genisto pilosae-Callunetum and Deschampsia flexuosa-Vaccinium
myrtillus community). At both sides the Diphasiastrum species are growing on
strongly acidic, moderately moist and sandy to loamy soil. One of the growing sites is
full sunny, the other is half shaded. For each population, size, degree of fertility and
information about threat factors are given. Suggestions for a new threat assessment for
the Red Data Book of Hesse were made for two of the three observed Diphasiastrum
species.Dans les annĂ©es 2003â2004, plusieurs espĂšces de Lycopodes aplatis ont Ă©tĂ©
dĂ©couvertes dans lâOdenwald prĂšs de Beerfelden et Olfen. La prĂ©sence de D. oellgaardii
est dâune signification Ă©minente car il Ă©tait rĂ©putĂ© comme disparu de la Hesse depuis
bien 50 ans. En outre D. complanatum et D. tristachyum ont été découverts chacun dans
un lieu différent. Les espÚces de Diphasiastrum peuplent des sites secondaires anthropogÚnes (pistes de ski, talus en bordure des routes) prÚs de Beerfelden et Olfen. Du point
de vue syntaxonomique, la vĂ©gĂ©tation peut ĂȘtre classĂ©e dans lâordre des Ulicetalia minoris
au Genisto pilosae-Callunetum ou à la communauté de Deschampsia flexuosa-Vaccinium
myrtillus. Dans les deux stations, les Lycopodes aplatis poussent sur des sols
sableux argileux fortement acides, moyennement frais. Les stations sont ensoleillées ou
peu ombragées. A cÎté de paramÚtres biologiques de population tels que nombre de
pieds et fertilité, des indications de menace de disparition sont présentées. Une nouvelle
classification dans la Liste rouge de Hesse pour 2 des 3 espĂšces de Diphasiastrum est
proposée
A P-band 5-way Unequal Split High Power Divider for SAR Applications
The design and test of 5-way high power divider operating at P-band for the airborne Synthetic Aperture Radar (SAR) system of DLR is presented. Distinctive features are high bandwidth, high power and an unequal power split on the 5 output ports
Eine Speicher- und Zugriffsarchitektur fĂŒr effiziente Anfragebearbeitung in Geo-Datenbankensystemen
Abstract involutions of algebraic groups and of Kac-Moody groups
Based on the second author's thesis in this article we provide a uniform
treatment of abstract involutions of algebraic groups and of Kac-Moody groups
using twin buildings, RGD systems, and twisted involutions of Coxeter groups.
Notably we simultaneously generalize the double coset decompositions
established by Springer and by Helminck-Wang for algebraic groups and by
Kac-Wang for certain Kac-Moody groups, we analyze the filtration studied by
Devillers-Muhlherr in the context of arbitrary involutions, and we answer a
structural question on the combinatorics of involutions of twin buildings
raised by Bennett-Gramlich-Hoffman-Shpectorov
Bistatic Experiment Using TerraSAR-X and DLRâs new F-SAR System
A bistatic X-band experiment was successfully performed early November 2007. TerraSAR-X was used as transmitter and DLRâs new airborne radar system F-SAR, which was programmed to acquire data in a quasi-continuous mode to avoid echo window synchronization issues, was used as bistatic receiver. Precise phase and time referencing between both systems, which is essential for obtaining high resolution SAR images, was derived during the bistatic processing. Hardware setup and performance analyses of the bistatic configuration are pre-sented together with first processing results that verify the predicted synchronization and imaging performance
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