Ocean Surface Observations Using the TanDEM-X Satellite Formation

The TanDEM-X SAR satellite formation permits improved ocean surface observations by means of bistatic along-track interferometry (ATI) when compared to single-satellite systems. The flexible imaging geometry of its two cooperating SAR sensors forms an interferometer that can achieve very high sensitivity to motions of objects on ground. This way, radar imaging of surface currents with unprecedented accuracy, high spatial resolution and wide coverage at the same time becomes possible. We demonstrate the capabilities of the sensor in the contexts of tidal current mapping, measurement of thermohaline and wind-driven ocean currents as well as detection of areas with surface films. We have developed a dedicated postprocessing system for TanDEM-X image products that allows extracting surface current information from the data. By this paper, we address bistatic data acquisition and processing aspects for sea surface imaging with TanDEM-X like interferometric baseline geometry, temporal decorrelation, and phase calibration. We present a variety of examples of data evaluation that clearly demonstrate the application potential of the methodology

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

Collective Absorption Dynamics and Enhancement in Deformed Targets

The interaction of intense fs laser pulses with thin foils that have an imposed deformation is compared with thick targets that develop bow shocks. Both target types yield good absorption. Up to 80% absorption is obtained for a $0.2\mu m$ thick, 15 times over-dense foil at $4 \cdot 10^{18} W/cm^2$. A value of 50% is obtained for a $4 \mu m$ thick, 2 times over-dense thick target at $10^{18} W/cm^2$. For comparable extension and curvature of the laser-plasma interfaces absorption levels in both targets become similar. In both absorption scales weakly with intensity and density. Energy transport in thin foils and thick targets, however, is different.Comment: 4 pages, 5 figures, Fig. 5 has been replace

Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere

Three-dimensional numerical simulations with CO5BOLD, a new radiation hydrodynamics code, result in a dynamic, thermally bifurcated model of the non-magnetic chromosphere of the quiet Sun. The 3-D model includes the middle and low chromosphere, the photosphere, and the top of the convection zone, where acoustic waves are excited by convective motions. While the waves propagate upwards, they steepen into shocks, dissipate, and deposit their mechanical energy as heat in the chromosphere. Our numerical simulations show for the first time a complex 3-D structure of the chromospheric layers, formed by the interaction of shock waves. Horizontal temperature cross-sections of the model chromosphere exhibit a network of hot filaments and enclosed cool regions. The horizontal pattern evolves on short time-scales of the order of typically 20 - 25 seconds, and has spatial scales comparable to those of the underlying granulation. The resulting thermal bifurcation, i.e., the co-existence of cold and hot regions, provides temperatures high enough to produce the observed chromospheric UV emission and -- at the same time -- temperatures cold enough to allow the formation of molecules (e.g., carbon monoxide). Our 3-D model corroborates the finding by Carlsson & Stein (1994) that the chromospheric temperature rise of semi-empirical models does not necessarily imply an increase in the average gas temperature but can be explained by the presence of substantial spatial and temporal temperature inhomogeneities.Comment: 18 pages, 13 figures, accepted by Astronomy & Astrophysics (30/10/03

Metabolic network modeling of redox balancing and biohydrogen production in purple nonsulfur bacteria

<p>Abstract</p> <p>Background</p> <p>Purple nonsulfur bacteria (PNSB) are facultative photosynthetic bacteria and exhibit an extremely versatile metabolism. A central focus of research on PNSB dealt with the elucidation of mechanisms by which they manage to balance cellular redox under diverse conditions, in particular under photoheterotrophic growth.</p> <p>Results</p> <p>Given the complexity of the central metabolism of PNSB, metabolic modeling becomes crucial for an integrated analysis of the accumulated biological knowledge. We reconstructed a stoichiometric model capturing the central metabolism of three important representatives of PNSB (<it>Rhodospirillum rubrum, Rhodobacter sphaeroides </it>and <it>Rhodopseudomonas palustris)</it>. Using flux variability analysis, the model reveals key metabolic constraints related to redox homeostasis in these bacteria. With the help of the model we can (i) give quantitative explanations for non-intuitive, partially species-specific phenomena of photoheterotrophic growth of PNSB, (ii) reproduce various quantitative experimental data, and (iii) formulate several new hypotheses. For example, model analysis of photoheterotrophic growth reveals that - despite a large number of utilizable catabolic pathways - substrate-specific biomass and CO₂yields are fixed constraints, irrespective of the assumption of optimal growth. Furthermore, our model explains quantitatively why a CO₂fixing pathway such as the Calvin cycle is required by PNSB for many substrates (even if CO₂is released). We also analyze the role of other pathways potentially involved in redox metabolism and how they affect quantitatively the required capacity of the Calvin cycle. Our model also enables us to discriminate between different acetate assimilation pathways that were proposed recently for <it>R. sphaeroides </it>and <it>R. rubrum</it>, both lacking the isocitrate lyase. Finally, we demonstrate the value of the metabolic model also for potential biotechnological applications: we examine the theoretical capabilities of PNSB for photoheterotrophic hydrogen production and identify suitable genetic interventions to increase the hydrogen yield.</p> <p>Conclusions</p> <p>Taken together, the metabolic model (i) explains various redox-related phenomena of the versatile metabolism of PNSB, (ii) delivers new hypotheses on the operation and relevance of several metabolic pathways, and (iii) holds significant potential as a tool for rational metabolic engineering of PNSB in biotechnological applications.</p

An Interferometric SAR Satellite Mission

The paper provides a critical review of the achievements in SAR interferometry from the ERS mission as well as from the Shuttle Radar Topography Mission SRTM. It describes the development from the original idea of the Interferometric Cartwheel to the concept of a formation flight of identical and active SAR satellites. From the experience gained from ERS and SRTM interferometric data processing as well as from the analysis of the Cartwheel concept a list of mission requirements has been set up. The most demanding one is the autonomous configuration flight of a tight x-band constellation, where the satellites fly as close as up to 30 m with a dead-band of +/- 10 m. The guidance, navigation and control considerations come to the conclusion that such a mission is feasible

Schiffsdetektion in Interferometrie-Radardaten

Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Ermittlung je einer Position und einer Fahrtrichtung für ein oder mehrere im Wasser fahrende Wasserfahrzeuge aus Interferometrie-Radardaten, in denen die Wasserfahrzeuge und die Wasserfahrzeuge umgebende Wasseroberflächen abgebildet sind. Das vorgeschlagene Verfahren umfassend folgende Schritte: Bereitstellen (101) der Radardaten als 2D-Interferogrammdaten INT1(x, y); Segmentieren (104) der 2D Interferogrammdaten INT1(x, y) zur Ermittlung von segmentierten 2D-Interferogrammdaten INT2(x, y), wobei die segmentierten 2D-Interferogrammdaten INT2(x, y) nur 2D-Datenbereiche Bn der 2DInterferogrammdaten INT1(x, y) umfassen, die jeweils ein zusammenhängendes Streifenmuster, sogenanntes Fringe-Pattern, wiedergeben, mit n = 1, 2, ...; Ermitteln (106) einer Kontur für jeden der 2D-Datenbereiche Bn; Ermitteln (108) eines Schwerpunktes für jeden der 2D-Datenbereiche Bn, wobei weiterhin für jeden der 2D-Datenbereiche Bn die Position eines Wasserfahrzeugs auf Basis des Schwerpunktes ermittelt wird; Ermitteln (109) einer geometrischen Ausrichtung des in den Daten jedes 2D-Datenbereichs Bi abgebildeten Streifenmusters relativ zu einer Bildachse der 2D-Interferogrammdaten INT1(x, y); und für jeden der 2D-Datenbereiche Bn abhängig von der ermittelten Ausrichtung des Streifenmusters, und der ermittelten Form der Kontur des jeweiligen 2D-Datenbereichs Bn Ermitteln (110) der Fahrtrichtung des jeweiligen Wasserfahrzeugs

First Results Of TanDEM-X Along-Track Interferometry

The interferometric imaging modes of the TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) satellite formation offer improved along-track interferometric capabilities e.g. through longer and multiple baselines. While the first provide high sensitivities to ground motions, the latter enable to resolve ambiguities. The extraction of motion information from TanDEM-X data by means of ATI is challenging due to the hybrid nature of the interferometric baseline. This is generally composed of an across-track (XTI) and an along-track interferometric (ATI) component BATI and requires a separation of the respective interferometric phase contributions

Handlungsgrundlage zur Bedarfsanerkennung von Düngemaßnahmen gemäß Anhang I und II der Verordnung (EWG) Nr. 2092/91 über den ökologischen Landbau

In den Erzeugervorschriften der Verordnung (EWG) Nr. 2092/91 sind lediglich Rahmenbedingungen festgelegt worden für die Bedarfsanerkennung von Düngungsmaßnahmen auf dem Öko-Betrieb. Als Ergebnis eines längeren Diskussionsprozesses wurde nachfolgende Handlungsgrundlage für Landwirte und Kontrollstellen des Ökologischen Landbaus zur Bedarfsanerkennung von Düngungsmaßnahmen gemäß Anhang I und II der Verordnung erstellt. In den Handlungsvorgaben und einem Leitfaden werden die fachlichen Grundlagen aufgeführt, so dass eine Entscheidungsfindung zur Bedarfsanerkennung von Düngungsmaßnahmen erleichtert wird

Temperature-driven transition from a semiconductor to a topological insulator

We report on a temperature-induced transition from a conventional semiconductor to a two-dimensional topological insulator investigated by means of magnetotransport experiments on HgTe/CdTe quantum well structures. At low temperatures, we are in the regime of the quantum spin Hall effect and observe an ambipolar quantized Hall resistance by tuning the Fermi energy through the bulk band gap. At room temperature, we find electron and hole conduction that can be described by a classical two-carrier model. Above the onset of quantized magnetotransport at low temperature, we observe a pronounced linear magnetoresistance that develops from a classical quadratic low-field magnetoresistance if electrons and holes coexist. Temperature-dependent bulk band structure calculations predict a transition from a conventional semiconductor to a topological insulator in the regime where the linear magnetoresistance occurs.Comment: 7 pages, 6 figure