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Institute Seminar - Presentations 2014
Sulabh Tiwari "Development of an efficient and portable orbital raw data simulator and processor for the scientific evaluation of experimental spaceborne-airborne bistatic SAR acquisitions"
Dienstag, 16. Dezember 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The bistatic raw data simulator is an important tool for designing future experiments, evaluating configurations, and testing the SAR focussing kernels, as well as innovative processing and calibration techniques. The development of the above simulator is done in Python.
Daniel Rosigkeit "Verwendbarkeit von LTE im DLR Forschungsflugzeug DO 228-212"
Donnerstag, 04. Dezember 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Diese Arbeit beinhaltet die Untersuchung der Verwendbarkeit von Long Term Evolution (LTE) für den Flugzeugbetrieb in einer operativen Höhe von 2000 bis 3000 Metern über Grund. Speziell für das DLR Forschungsprojekt VABENE++, welches sich mit Verkehrsmanagement bei Großereignissen und Katastrophenschutz beschäftigt, ist diese Datenübertragung von hohem Interesse. Verkehrsdaten und Radarbilder sollen in Echtzeit an einen Server am Boden übermittelt werden, wo sie beispielsweise an Behörden und Organisationen mit Sicherheitsaufgaben weitergeleitet werden können. Der Inhalt dieser Masterarbeit beschäftigt sich mit der technischen Umsetzung der Datenübertragung. Diese wird mit Hilfe eines handelsüblichen LTE Modems umgesetzt, welches eine Verbindung zu den vorhandenen LTE Sendemasten am Boden aufbauen soll. Die Arbeit beinhaltet theoretische Analysen, sowie Simulationen und Messungen im Forschungsflugzeug DO 228 mit abschließender Bewertung der Messdaten.
Keith Morrison "Detection of Aerial Features by Ground Diffraction Patterning in SAR Imagery"
Dienstag, 02. Dezember 2014
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
We report on an investigation into the secondary detection of objects in SAR imagery by the presence of diffraction patterning. Laboratory SAR imaging measurements were conducted on suspended targets above a gravel surface. Clear fringe patterns were seen across the imaged gravel in both backscatter and interferometric phase. Modelling was carried out using an incremental diffraction algorithm. The positioning and modulation characteristics of the fringes could be understood by the relative positioning of the targets above the gravel and the imaging geometries. Even if the targets are not visible in the imagery from the direct return, their presence might still be inferred from the presence of ground fringes. The technique might be useful for collision avoidance for low-flying aircraft, or for surveillance and security purposes.
Ponnurangam Gramini Ganesan "Soil Moisture Estimation using Hybrid Polarimetric RiSAT Data"
Dienstag, 25. November 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In this seminar, the capabilities of hybrid Polarimetric SAR (PolSAR) to estimate soil moisture on bare and vegetated agricultural soils will be presented. A new methodology based on a compact polarimetric decomposition together with a surface component inversion was developed to retrieve surface soil moisture. A model-based compact decomposition technique is used to obtain the surface scattering component under the assumption of a randomly oriented vegetation volume. After vegetation removal, the surface scattering component is inverted for soil moisture by comparison with a rank-1surface scattering component modeled by the IEM or X-Bragg model. Hence, the developed, hybrid polarimetric methodology is based on a two-layer (Random-Volume-over-Ground) scattering model for agriculture. Therefore, the inversion results can be obtained for both, bare and vegetated soils. The developed algorithm is applied on a time series of hybrid polarimetric C-band RISAT-1 RCTLR (Right Circular Transmit Linear Receive) data acquired from April to October 2014 over the Wallerfing test site in Lower Bavaria, Germany. Intensive ground measurements of soil and vegetation parameters for four different agriculture crop types (corn, cucumber, sugar beet and wheat) were collected synchronously with the satellite overpasses by DLR-HR, ETH Zurich and LMU Munich. In order to validate the developed algorithm, the estimated soil moisture from the hybrid PolSAR is compared with ground measured soil moisture for a detailed quality assessment on (smooth/rough) bare and vegetated soils. Including the entire growing season (all dates) and all crop types, the estimated soil moisture values indicate an overall root mean square (RMS) error of 7 or 10 vol% using the X-Bragg or IEM model. The time series analysis encourages the retrieval of soil moisture under a growing vegetation cover using hybrid PolSAR data at C-band.
Marwan Younis "SAR Polarimetry: An Instrument View"
Montag, 24. November 2014
14.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Polarimetry increases the information content of SAR acquisitions, which can be beneficial as has been demonstrated for various applications. A great deal of publications describe how to utilize the polarimetric information in the SAR image. The current work approaches polarimetry from an instrument and antenna point of view. It addresses the issue on how the instrument affects the polarimetric measurement and links it to a mathematical descriptions. This approach allows to understand aspects such as the difference between reflector and planar antenna SAR, the impact of using digital beamforming techniques (such as SCORE), or the contribution of the cross-polar pattern when processing (i.e. focusing) the raw data. Further, various issues such as circular polarized SAR, range ambiguities, Faraday rotation are mentioned. The aim is to arrive at a better understanding as necessary for the polarimetric calibration of SAR, especially in view of the Tandem-L mission.
Jesus Gustavo Cuevas Castillo "Implementation of a Bifocal Antenna Concept on a Dual Reflectarray System"
Freitag, 31. Oktober 2014
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Dual-reflectarrays antennas have been proposed as an economic and competitive alternative for multi beam and beam scanning applications. For multi-beam antennas, the adjustment of the phase-shift distribution on two surfaces provides additional degrees of freedom that can be used to minimize the degradation of the beams pointing at the edges of the coverage in a one feed per beam basis. These antennas are be a good alternative for radar applications, in which scan on receive is required. Two design methods based on a 3D ray tracing models to implement the principle of bifocal antennas using a dual-reflectarray configuration will be described. The methods are tested for two configurations: a centered antenna consisting of two parallel flat reflectarrays and dual offset reflectarray antenna.
Fairouz Stambouli "Digital Calibration of Multi-Channel SAR"
Dienstag, 28. Oktober 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In den letzten Jahrzehnten hat sich die Fernerkundung mit SAR (Radar mit synthetischer Apertur) signifikant weiterentwickelt, insbesondere für weltraumgestützte Systeme. SAR ist ein zukunftsträchtiges System mit der Fähigkeit, unabhängig von Tag und Nacht hochauflösende Bilder der Erdoberfläche zu liefern. Dank seiner vielen Einsatzmöglichkeiten, wie zum Beispiel die Umweltüberwachung, Meereskunde und Katastrophenmanagement, ist SAR eine zuverlässige Informationsquelle. Um die hohen Anforderungen an die Qualität der gelieferten Aufnahmen zu erfüllen, ist eine genaue Kalibrierung der aufgenommenen Messdaten notwendig. Hierfür kommen hochentwickelte Kalibrierverfahren zum Einsatz. Ein klarer Trend für zukünftige SAR Systeme ist die Nutzung von Techniken der digitalen Strahlformung. Eine Anwendung der jetzigen Kalibrierverfahren auf derartigen Mehrkanal SAR-Systemen ist nur mit erheblichem Aufwand möglich und erfordert eine hohe Komplexität. Des Weiteren sind diese Verfahren nicht in der Lage, eine Kalibrierung in Echtzeit durchzuführen. Ein vielversprechender Kandidat ist die sogenannte digitale datenbasierte Kalibrierung, welche in dieser Arbeit untersucht wird. Dabei sind die Fehler anhand der eigentlichen SAR-Messdaten bestimmt.
Philipp Posovszky "Kurz-Einführung in den Lync-Client"
Donnerstag, 23. Oktober 2014
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Eine kleine Live Demo des Lync-Client: kurze Vorstellung der Kernfunktionen des Lync-Clients. Beispielsweise das Teilen von Bildschirminhalten, übergeben der Kontrolle des Computers, Aktivitätsfeeds, Verfügbarkeitsstatus und Benachrichtigungen über Statusänderungen.
Klemen Koselj "Bat echolocation: fully autonomous sensing technology optimized through evolution"
Dienstag, 21. Oktober 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Bats are the only mammals that are capable of active sustained flight. More than fifty million years ago they evolved another peculiar feature that enabled them to conquer the nightly airspace: echolocation. Over thousand species of bat emit tonal ultrasonic pulses. Using their echoes from surrounding objects bats are able to localise and recognise the objects, navigate around in complete darkness and efficiently fill their stomachs with food that is not accessible to other animals. Echolocation bears many similarities to human active sensing technology like radar and there is a lot that radar engineers can learn from bats and bat researchers from the radar. However, there is one important difference. Echolocation was optimised in the process of evolution, which cannot afford very large costs and is limited with hardware and constructing parts that are available. I will present different types of successful echolocation solutions and costs and benefits that have shaped them. I will show how bats dynamically adjust signal parameters to control the amount of information that needs to be processed. We recently acquired the first evidence that bats are even capable of orientation from the echoes of other individual’s calls, which opens the possibility for sensory cooperation among echolocators. The talk is targeted at anybody working with radar that would like to find out more about the natural colleagues – bats.
Sebastian Iff "Untersuchungen zum Nachweis von SAR-Bildqualitätsparametern"
Montag, 29. September 2014
14.45 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Thematischer Hintergrund: Es geht in der Arbeit darum, wie sich unterschiedliche Einflüsse der Umgebung eines Punktziels (z. B. Atmosphäre, Clutter, Imperfektionen eines Referenzziels) auf die Stabilität von Bildqualitätsparametern auswirken. Die Schwankungsintervalle der einzelnen Parameter müssen z.B. im Design eines Sensors als Performance-Reserve vorgehalten werden.
Heinrich Axt "Vergleichende Analyse von Antennenkonzepten für P-Band Kalibriertransponder"
Montag, 29. September 2014
13.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Bei der Transponderentwicklung für die SAR-Kalibrierung nimmt die Antennenentwicklung eine zentrale Rolle bei elektrischem und mechnischem Design ein. Speziell im P-Band mussten bisher wegen der geringen Frequenz und der resultierenden Baugröße Abstriche bei Antenneneigenschaften wie der Nebenkeulen- und kreuzpolaren Unterdrückung in Kauf genommen werden. In dieser Arbeit werden bestehende Antennenkonzepte verglichen, ein neuer Hornantennentyp genauer untersucht, aufgebaut und vermessen. Es kann gezeigt werden, dass der neue Antennentyp gepaart mit neuen Fertigungstechniken hochgenaue Kalibriertransponder zukünftig auch im P-Band erlauben wird.
Sebastian Gehrig "Untersuchung zur Abbildungsqualität und Absolutwertgenauigkeit eines hochauflösenden Pulsradars"
Montag, 29. September 2014
11.15 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In den letzten Jahren ist der Bedarf an hochauflösenden Radarsignaturen zur Objekterkennung und Unterstützung von Simulationswerkzeugen stetig gewachsen. Um eine hochwertige und schnelle Datenaufnahme zu erzielen, sowie neue Radartechniken zu verifizieren (z.B. MIMO, DBF, kodierte Wellenformen), wird seit einiger Zeit das GigaRad-Instrument aufgebaut, welches prinzipiell einen beliebig modulierten breitbandigen Puls sendet und mittels Hochfrequenzabtaster die Empfangssignale im Zeitbereich digitalisiert und dadurch eine sehr flexible Datenverarbeitung erlaubt. Im Rahmen dieser Arbeit wurde nun die interne wie auch externe Kalibrierung und Charakterisierung des Radarinstruments bezüglich der erreichbaren Genauigkeit durchgeführt und wichtige Systemparameter bestimmt und beurteilt. Dazu wurde das interne Kalibrationsverfahren automatisiert, statischen Szenen aufgenommen, sowie hochauflösender Abbildungen im ISAR-Betrieb durchgeführt.
Sara Marongiu "Estimation of Vertical Structure of Forest from Multi-Baseline SAR Data: A Performance Analysis"
Dienstag, 23. September 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The knowledge of the vertical forest structure and of its changes in space and time is fundamental e.g. for the assessment of heterogeneity, biodiversity, disturbance regime, and for the development of robust and accurate biomass estimators. Synthetic aperture radar (SAR) systems will play an essential role in establishing a continuous, systematic and global forest observation framework. Indeed, they provide the unique ability to image large areas at high spatial and temporal resolution, and at the same time they penetrate into the forest volume providing information about its vertical structure. Among the different SAR techniques that have been developed in the last decades, SAR Tomography (TomoSAR) allows the estimation of the 3-D distribution of the backscattered power from multiple SAR images, thus providing a proxy to forest vertical structure. Although TomoSAR is an established technique with several algorithmic implementations, there is still a lack of performance analyses characterizing the TomoSAR information extraction with respect to system constraints and forest structure product requirements. In this Seminar, results of a performance analysis will be presented considering the reconstruction of forest structure based on the Capon spectral estimator. Taking as a reference a number of meaningful backscattering profiles, the obtained Capon tomograms have been decomposed into a sum of Gaussian-shaped functions (interpreted as forest layers). In this way, each continuous power profiles could be discretized into a limited set of parameters, and the estimation performance could be evaluated in terms of the root mean squared error associated to each of them by means of Monte Carlo simulations. In a second stage, the capability to distinguish between different profiles has been evaluated. In this case, the performance has been quantified as the probability of correct detection of the changes of the layer parameters. For both TomoSAR profile estimation and profile change detection, the performance indicators have been evaluated as a function of e.g. tomographic height resolution (i.e. maximum baseline length), number of acquisitions and number of looks. The results of this analysis are expected to contribute to spaceborne system studies (like Tandem-L) aimed at optimizing acquisition strategies for forest structure observation in order to meet product requirements.
Jesus Lloredo "Joint phase unwrapping for multifrequency SAR Interferometry"
Dienstag, 05. August 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
An important step in the interferometric processing chain is the phase unwrapping, which transforms the ambiguous phase (wrapped in the interval -/+ 180°) in an unambiguous phase. This unambiguous phase can then be used for the computation of the scene height model. Standard phase unwrapping methods work with data from a single frequency and a single baseline at a time. The unwrapping becomes extremely challenging for data with small height of ambiguity (HoA), which is usually the case when working with high frequencies and large baselines. The use of multichannel information can help to solve the ambiguities, improving the unwrapping results. However, for airborne repeat-pass InSAR data, the presence of uncompensated residual motion errors usually affects the efficiency of multibaseline approaches. For systems capable of acquiring data simultaneously in different frequency bands, as is the case of the F-SAR of DLR, multifrequency approaches can be explored to cope with the residual errors issue. In this thesis, different unwrapping algorithms are evaluated for the unwrapping of data with small height of ambiguity. Furthermore, methods to jointly unwrap interferograms from multifrequency acquisitions in a robust manner are analyzed.
Stefan Baumgartner "Traffic Monitoring with Air- and Spaceborne Synthetic Aperture Radar"
Donnerstag, 24. Juli 2014
11.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic aperture radar (SAR) is an established imaging method widely used by the remote sensing community. It enables two-dimensional wide-swath imaging of the Earth's surface, independent of sunlight illumination and, depending on the used wavelength, almost independent of the weather. With conventional single-channel SAR and SAR processing only stationary, non-moving targets are imaged correctly. In contrast, moving targets appear generally blurred and displaced from their actual position in the SAR image. The reason is the additional Doppler shift caused by the target motion. Often moving targets with low radar cross section are even invisible since they are covered by the signals of the clutter background. By extending the SAR with additional receiving antennas, separated in flight direction by a certain along-track baseline, wide area traffic monitoring becomes feasible. The additional receiving channels enable clutter suppression and, hence, the detection of moving vehicles with comparatively low radar cross section. With suitable multi-channel algorithms the actual vehicle positions and velocities can be estimated additionally. Many algorithms treated in the literature so far either enable only one-dimensional velocity estimation, or an inaccurate two-dimensional velocity estimation which is severely biased by possible target accelerations or by the required target tracking. Furthermore, especially for spaceborne SAR systems, the algorithms may lead to an unsatisfying position estimation accuracy. At the beginning of the present doctoral thesis the effects on SAR imagery caused by moving targets are investigated in detail and state-of-the-art parameter estimation methods are discussed. Based on these investigations and on the estimation methods three novel algorithms well suited for radar-based traffic monitoring are developed, discussed in detail and verified using real multi-channel SAR data. The first two algorithms are for multi-channel airborne SAR systems. Both of them enable an accurate and acceleration independent two-dimensional velocity estimation. The first algorithm does not rely on a priori knowledge and can therefore by applied for monitoring traffic on unknown paths or open areas. The second one includes a road database. This has the advantage that only the areas around the a priori known roads have to be scanned for moving targets. As a consequence, the algorithm has real-time capability. The third algorithm is suited for spaceborne traffic monitoring with two SAR platforms flying in a tandem configuration with platform separations in the order of a few seconds. For this, a novel method for two-dimensional velocity estimation was developed, which additionally enables target position estimation with very high accuracy without the need of any a priori knowledge.
Benjamin Bräutigam "Instrument Calibration of Spaceborne SAR Systems"
Mittwoch, 23. Juli 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Die Kalibrierung von Radarsystemen mit synthetischer Apertur (SAR) ermöglicht die Konvertierung von Grauwerten in SAR-Bildern in geophysikalische Einheiten wie dem Radarrückstreuquerschnitt und der geographischen Koordinate eines SAR-Pixels. Eine besondere Herausforderung stellt die Vielseitigkeit moderner SAR-Satelliten dar, deren Radarsensoren mit flexiblen Betriebsarten und einer Vielzahl von unterschiedlichen Antennenschwenkmöglichkeiten ausgerüstet sind. Hierbei spielt die interne Kalibrierung eine wesentliche Rolle, da sie die kontinuierliche Überwachung und Kompensation des Instrumentverhaltens regelt. Die zunehmende Komplexität der Radar-Instrumente erfordert folglich auch eine Verbesserung des internen Kalibrierkonzepts, um den Herausforderungen zukünftiger SAR-Systeme gerecht zu werden. Das Seminar stellt hierzu ein Konzept zur Korrektur von systematischen Instrumentenabweichungen sowie den Entwurf eines realistischen Optimalfilters zur Fokussierung von SAR-Rohdaten in Entfernungsrichtung vor. In einem weiteren Schritt wird eine innovative Methode zur Überwachung von aktiven Array-Antennen diskutiert, die mithilfe individueller Codes einzelne Antennenarrayelemente während des Betriebs vermessen und bewerten kann. Im Vortrag werden diese neuentwickelten Kalibrierprozeduren und Modelle anhand von Messergebnissen mit TerraSAR-X vorgestellt.
Aniello Sorrentino "Investigation of Polarimetric Active/Passive Microwave Scattering towards Soil Moisture Estimation"
Montag, 26. Mai 2014
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
With the upcoming Soil Moisture Active Passive (SMAP) mission, scheduled for launch in November 2014, the investigation of active/passive microwave scattering/emission gains significantly in importance. The objective of this master thesis is the analysis of active/passive microwave signals over agricultural regions for the development of a combined soil moisture estimation algorithm. In active (SAR) and passive (radiometer) microwave remote sensing, polarimetry provides an innovative observation space for analyses of land surface scattering. For this, a unique data set was acquired at L-band in April and May 2013 over the TERENO Rur observatory, near Jülich in Western Germany. The active F-SAR sensor of DLR was operated together with the passive PLMR2 (radiometer) of the Research Centre Jülich (FZJ) in a multi-sensor configuration to acquire polarimetric, active-passive microwave data. The PLMR2 sensor features medium-resolution mapping of (incoherent) H- and V-polarized brightness temperatures at incidence angles +/-8°, +/-22° and +/-38° in across-track direction. The F SAR sensor obtains (coherent) fully polarimetric (HH/HV/VHVV) backscattering data of high spatial resolution (range: 4m, azimuth: 0.6m) in slant range direction. Investigations on the active-passive data set indicate significant sensitivity to the polarimetric observation space contained in the F-SAR and PLMR2 acquisitions. Results from the polarimetric analyses and inversions for development of a combined soil moisture estimation will be presented in the seminar together with first validations against ground measurements from the TERENO Rur observatory.
Eduardo Carrasco "Advanced Concepts for Reflectarray Antennas with Dynamic Reconfiguration"
Dienstag, 20. Mai 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Reflectarray antennas combine the main features of both parabolic reflectors and conventional arrays. Because of their spatially-fed architecture, they do not require lossy feeding networks, reducing the overall losses, manufacturing complexity and cost. A very important characteristic is that they allow the implementation of electronic control elements for dynamically reconfiguring the phase (and therefore the beam), the frequency and the polarization. The talk will include a brief introduction of basic concepts in reflectarrays, bandwidth improvement techniques, single and multilayer topologies; as well as advanced concepts for reconfiguring the beam, operation frequency and polarization. Some examples using solid state switches, micro-electromechanical systems (MEMS), liquid crystal substrates, liquid metal alloys and graphene will be shown.
Prof. Y. S. Rao "Full and Compact Polarimetric SAR Data Analysis for Various Land Features"
Montag, 12. Mai 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Compact polarimetry has some advantages over full polarimetry in terms of large area coverage, less power requirement and low data rate. So far, most of the work on compact-pol data was confined to simulated compact data from full-pol SAR data. Compact-pol data has been available operationally over the Earth since the launch of Indian RISAT-1 on April 26, 2012. Future missions ALOS-2, Canadian RCM and Argentina’s SAOCOM will also operate in compact pol mode. In this talk, the specifications of RISAT-1 and data products will be covered briefly. Synchronous with RISAT-1 passes, Radarsat-2 data were also acquired over two Indian test areas for the comparison of sigma-0 values and classification of various land covers using Wishart classifier. Compact decomposition theorems for understanding odd, even and volume scattering from various land features will be discussed. Various compact polarimetry parameters such as Circular Polarization Ratio (CPR), Linear Polarization Ratio (LPR), Degree of Circular Polarization (DoCP) and Degree of Linear Polarization (DoLP) will be presented for various land features.
Mariantonietta Zonno "Lack of phase triangularity in interferometric processing of SAR image stacks"
Dienstag, 06. Mai 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
This work investigates a little-known phenomenon that can arise in interferometry, the lack of congruence – or triangularity – in the phases of three multilooked interferograms made out of three coregistered images. It is generally expected that, among the three interferograms, one is redundant (apart from noise effects). The phase congruence hypothesis is commonly assumed in the most advanced InSAR algorithms for stacks (e.g. in SqueeSAR), precisely in order to filter the phases. However, sometimes phase triplets exhibit mismatches: if a systematic character is recognized, the lack of triangularity needs to be explained by physical causes. Among possible physical explanations there are soil moisture variations and volume scattering in the case of normal baseline variations. Discriminating between the two can be difficult. When the baseline configuration stays the same but phase patterns differ, it is possible to conclude that there is more than a pure volumetric effect. For example there could be moisture variations in soils or in the trees which affect the dielectric constant and consequently the propagation of the electromagnetic waves in the medium. The sum of the phases of three interferograms is invariant under phase calibration and it is therefore possible to detect some effects relying on phases even without using reference targets or PSI analyses. The presentation will show real-data examples at different frequencies together with some theoretical discussion.
Stefan Seel "Alphasat GEO laser relay commissioning status and EDRS GEO relay outlook"
Dienstag, 25. März 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In-orbit commissioning of the first geostationary laser communication terminal (TESAT LCT) of the EDRS 1,800 Mbps class has commenced. The laser relay experiments phase is being contracted for three years by the German Space Agency (DLR) and is planned to see test campaigns with an optical ground station of ESA at Tenerife, a transportable ground station with adaptive optics (TESAT T-AOGS) and two low earth orbiting Earth observation satellites (Sentinel-1A and Sentinel-2A) as well as an airborne platform. The Alphasat satellite carrying several European technology demonstrator payloads (TDP) has been launched on July 25th, 2013 from Kourou. The TDP1 comprises a laser terminal (LCT) capable of transmitting and receiving 1,800 Mbps at 1064nm. The Alphasat-LCT design stems from the NFIRE- and TerraSAR-X LCT design that has two flight units on orbit since 2007 and verified coherent detection BPSK for intersatellite and space-to-ground links.. In the initial orbit position at 008 East the Alphasat LCT went through wake-up, launch lock release and a full communication self test. The integrity of data transmission along the complete electro-optical path has been verified. After transition to the final orbit position at 025 East the technology demonstrator payload switched on the 26.5 GHz Ka-band subsystem which is used to transmit up to 600 Mbps of LCT-collected data to a footprint centered around Oberpfaffenhofen near Munich, Germany. The ground segment there is operated by DFD and verified the performance of the Ka-band downlink using test data locally generated on the Alphasat satellite. First light event took place in late August when the optical pointing system of the LCT was directed towards an ESA operated ground station on mount Teide, Tenerife (Spain). The laser beam has been received on ground and an uplink laser seen and tracked by the Alphasat LCT. We expect an extension of the original commissioning plan to be contracted within end of 2013 the Alphasat LCT that allows communication experiments through atmosphere. For these tests the Teide ESA station and a transportable optical ground station of DLR/TESAT will be used. As an outlook to relay communications for Space and Earth exploration the Alphasat LCT commissioning will proceed to intersatellite links as soon as the lower Earth orbit Sentinel-1A or Sentinel-2A satellites will have been launched. The 1,800 Mbps class LCT is designed to provide near-time communication links to the mission control center via a 45,000 km GEO relay satellite station like Alphasat. The first such operational service implementation will be the public-private partnership program EDRS of the European Space Agency ESA and Astrium Services (ASV). The Alphasat LCT commissioning will provide very valuable performance verification and opportunity to optimize the operational LCT relay parameters. The Alphasat LCT-TDP 1 project, which this publication is based on, is carried out on behalf of the Space Administration of the German Aerospace Center (DLR e.V.) an it is funded on behalf of DLR by the Federal Ministry of Economics and Technology based on legislation by the German Parliament, kept under the reference number 50 YH 0632. The authors are responsible for the contents of the publication.. Corresponding Author: Stefan U. Seel Authors: Daniel Troendle, Frank Heine, Herwig Zech, Matthias Motzigemba, Hartmut Kaempfner, Uwe Sterr (ST2C) and Rolf Meyer (DLR)
Vincenzo Del Zoppo "On-Board Doppler Filtering for Data Volume Reduction in Spaceborne SAR Systems"
Montag, 24. März 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
High-resolution wide-swath (HRWS) synthetic aperture radar (SAR) systems based on digital beamforming (DBF) in elevation are very attractive for the observation of dynamic processes on the Earth’s surface. However, HRWS systems are inherently associated with a huge data volume. Moreover, in order to comply with azimuth ambiguity requirements, a pulse repetition frequency (PRF) much higher than the desired processed Doppler bandwidth is often desirable. The data volume can be drastically reduced, if on-board Doppler filtering and decimation are performed prior to downlink. A finite impulse response (FIR) filter with a relatively small number of taps suffices to completely suppress the additional ambiguous components and recover the original impulse response, provided that the filter’s transfer function is compensated for in the processing. This strategy is also applicable to staggered SAR systems, where on-board Doppler filtering and resampling can be jointly implemented.
Sigurd Huber "Spaceborne SAR Systems with Digital Beamforming and Reflector Antenna"
Montag, 24. Februar 2014
09.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Contactless information retrieval using electromagnetic waves plays an increasingly important role for scientific and industrial progress. In particular the synthetic aperture radar (SAR) principle, numbered among the imaging techniques, nowadays belongs to the standard-repertoire of civil and military Earth observation. Future SAR systems, whose performance significantly depends on the employed hardware as well as the data processing, shall map increasingly large areas in shorter and shorter time intervals. The work at hand deals with sensor systems, whose two main parts encompass antenna techniques, as well as the subsequent analog and digital signal processing. Here, the focus lies on digital beamforming techniques, enabling an efficient operation of the SAR sensor. For this, space-time adaptive algorithms are derived, which are suitable to minimize the system noise of the sensor and to suppress spatial interference. These algorithms are simulated using the example of a spaceborne SAR system, where the innovative concept of a large unfoldable reflector in combination with a digital feed array is employed. The purpose of such a radar type is to digitize the electromagnetic signal almost immediately after the receiver, in order to ensure the maximal flexibility of the SAR system and to save costs for expensive analog electronics at the same time. The second emphasis of this work deals with optimization aspects, where amongst others a new method is proposed, which allows to mitigate an inherent problematic of such reflector-feed-array constellations. Since in the event of a failure of a single or multiple elements of the feed array a blind spot in the field of view is generated, as solution a defocused reflector antenna concept is proposed. Such an antenna concept combines the merit of planar array antennas, namely the preservation of the functionality in case of an antenna element failure, with the advantage of unfurlable reflector antennas, which is the realization of large apertures.
Peter Edenhofer "Das Radar-Transmissionsexperiment CONSERT der ESA-Kometenmission Rosetta und die erstmalige Erkundung eines Kometenkerns"
Dienstag, 11. Februar 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Ausgehend von der ESA-Kometensonde Giotto und ihrem erfolgreichen Vorbeiflug am Kometen Halley 1986 hat nunmehr die 2004 gestartete Kometenmission Rosetta der ESA erstmals die Landung auf einem Kometen zum Ziel, um Antworten auf Fragen nach der Entstehung unseres Sonnensystems zu suchen. Nach jahrelangem Transferflug sind Wake-Up und Landung für Januar bzw. November 2014 geplant. Es wird ein kurzer zusammenfassender Überblick gegeben über die wissenschaftliche Nutzlast des Rosetta Orbiters und insbesondere des Philae Landers mit jeweils 10 Experimenten. Das Radar-Transmissionsexperiment CONSERT (PI Universität Grenoble) arbeitet hierbei sende- und empfangsseitig mit einem am Rosetta Orbiter platzierten zirkular polarisierten 90-MHz-Trägerfrequenzsignal, das mittels Transponder auf dem Philae Lander an der gegenüberliegenden Kometenseite in Okkultationsstellung pro Orbit umgesetzt wird. Primäres wissenschaftliches Ziel dieses quasi-tomographischen Messkonzepts ist es, zum ersten Mal überhaupt die innere Struktur eines Kometenkerns zu erforschen. Es wird berichtet über ausgewählte rechner- und laborgestützte Simulationen zur technischen Ausrüstung (z.B. Strahlungskopplungseffekte der Antennen am Orbiter und Lander, Polarisationsverluste abhängig von der Strahlrichtung), zu Inflight-Kalibrationen und 2D/3D-fraktalen Computersimulationen u.a. mit speziellen numerisch stabilen kovarianzgestützten Inversionsmethoden der Fernerkundung (Remote Sensing) bei Laufzeitmessungen. Abschliessend wird auf erste erdgebundene Beobachtungen des Zielkometen eingegangen und ein Ausblick gegeben über den zu erwartenden Operationsverlauf z.B. am ESOC und beteiligten Forschungsinstituten. Ein kurzer Videofilm verdeutlicht Simulationen z.B. eines Landemanövers.
Carolina Lautz "Das DLR-Bildungsprogramm 2014 – neue und bewährte Qualifizierungsangebote für eine gezielte fachliche und persönliche Weiterentwicklung"
Dienstag, 04. Februar 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Ihre neue Personalentwicklerin am Standort Oberpfaffenhofen stellt sich und das DLR-Bildungsprogramm 2014 für Mitarbeiterinnen und Mitarbeiter vor. Orientiert an den systematisch erhobenen Qualifizierungsbedarfen der Institute und Einrichtungen ist das Fortbildungsangebot weiterentwickelt und erweitert worden. Was ist neu? Welche Angebote haben sich bewährt? Sie bekommen einen Überblick über das vielfältige Angebot und erfahren, wie Sie die geeigneten Seminare und Trainings für sich und/oder Ihre MitarbeiterInnen identifizieren.
Thomas Kraus "Global Performance Assessment for the TerraSAR-X Staring Spotlight and Wide ScanSAR Modes"
Dienstag, 28. Januar 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
For the TerraSAR-X mission two new modes have been implemented and are operational since autumn 2013. One is a high azimuth resolution Staring Spotlight mode and the other a wide ScanSAR mode with doubled ground range coverage compared to the nominal TerraSAR-X ScanSAR. For both modes detailed performance analyses have been conducted in order to optimize the commanding parameters. Compared to the previously available TerraSAR-X imaging modes Staring Spotlight and wide ScanSAR require to operate the instrument with minimum margins and at the edge of the specifications the radar was designed for. Therefore an additional step – a global acquisition simulation and analysis – was introduced during the operationalization to ensure the suitability of the derived commanding parameters on a global scale. The talk gives an overview about SAR performance analysis conducted during the mode optimization and implementation phases and focusses on a global performance assessment approach. Additionally exemplary acquisitions and measurement results will be shown.
Ezgi Özis "Metamaterial Technologies for Microwave Radomes"
Freitag, 17. Januar 2014
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Metamaterial technologies open up new possibilities in the design of microwave radomes. The aim of this dissertation is to overview the current state of metamaterial technologies related to microwave radomes, to develop expertise in simulations of metamaterial structures with full wave electromagnetic simulation software and to get an understanding of the operation principles of metasheets. This work examines the scattering properties and polarizabilities of electrically small simply shaped particles (sphere, disc, wire, circular loop) and more complex bi-anisotropic particles (omega-shaped and chiral) which can be used as inclusions in metamaterial arrays. Equivalent radii for short wires with different cross sections are determined from the polarizability values calculated with HFSS. Resonant response of an array of bi-anisotropic particles (omega particle) and the effect of the dimensions of the inclusions on the reflection coefficient are analyzed.
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