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Vorträge im Institutsseminar 2007
Florian Kugler "Multi-Frequency Forest Height Estimation"
Dienstag, 11. Dezember 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Dmytro Vasylenko "Optimierung der Randkontur planarer UWB-Antennen via Inversion neuronaler Netze mit genetischen Algorithmen"
Donnerstag, 06. Dezember 2007
14:30 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Mehr
Karlus Alexander Camara de Macedo "New Processing Methodology for Airbone Repeat-Pass SAR Interferometry"
Dienstag, 04. Dezember 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Differential Synthetic Aperture Radar (SAR) interferometry is a technique to measure, using airborne or spaceborne imaging radar system, sub-wavelength terrain movement as a function of time. To enable such measurements repeat-pass SAR interferometry is performed, which consists of imaging the same area at different times to acquire SAR data and combine them to generate differential interferograms. The accuracy of these measurements depends on how coherent are the phase observations of a target seen by different radar acquisitions. Precise knowledge of the flight track is mandatory in order to keep the phase history coherent and perform sub-wavelengths measurements. Spaceborne SAR systems are able to describe a very stable trajectory and as a consequence differential interferometry derived from spaceborne data has become an established technique. Differently, airborne SAR systems are not able to describe a stable trajectory and therefore require the use of a modern navigation system in order to accurately track the position of the radar antenna. An extra processing step, called motion compensation, uses the navigation data to correct the phase errors arising from the track deviations to achieve coherent phase history.
In this thesis, a new processing methodology is proposed for repeat-pass SAR data with differential interferometry applications. The methodology adds two new processing steps after raw data focusing. The first step consists of a new motion compensation approach, capable of precisely correcting the topography- and aperture-dependent phase error that remains after raw data focusing and conventional motion compensation. The second step consists of a new and robust autofocus algorithm to estimate the motion deviations not measured by modern navigation systems, enhancing the accuracy of the input data for the motion compensation algorithm. This new methodology is unique in its solution because it allows accurate repeat-pass interferogram generation from SAR images in which the motion errors are independently compensated. The new methodology has the advantage that it does not require interferometric modeling and its performance does not depend on the spatial nor on the temporal baseline decorrelation.
Real airborne repeat-pass data of the E-SAR system of the German Aerospace Center are used to demonstrate the performance of the new methodology. In order to show the necessity and applicability of the new processing methodology, typical differential SAR measurements are performed with long temporal baselines and with time-series analysis. The permanent scatterers technique is investigated and applied for the first time for the airborne case.
Marcelo Albuquerque "Time-Domain Back-Projection Processing for Airborne SAR Applications"
Donnerstag, 29. November 2007
16:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
The Back-Projection Algorithm is a SAR processing approach that uses time-domain convolution in order to perform SAR focusing.
Some benefits of this approach are exact inversion, ideal motion compensation including topography information and handling of general aperture geometries. Applications of the algorithm are presented with respect to topography adaptive processing, direct generation of map projections and consideration of non linear trajectories.
Results of the processing of a circular flight SAR experiment are presented and perspectives of the geometry's capabilities are analysed.
Dr. Wolfgang Keydel "Vom Flugfunkforschungsinstitut Oberpfaffenhofen zum Institut für Hochfrequenztechnik und Radarsysteme"
Dienstag, 27. November 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Seit 70 Jahren ist der DLR-Standort Oberpfaffenhofen ein bedeutendes Forschungszentrum für Hochfrequenztechnik und Radar. Damals, im Oktober 1937, gründete Prof. Max Dieckmann mit Abteilungen seiner 1908 bestehenden „Drahtlostelegrafischen und Luftelektrischen Versuchsanstalt Gräfelfing“ (DVG) das „Flugfunkforschungsinstitut Oberpfaffenhofen“ (FFO) als selbständige Forschungseinrichtung auf vielfältigen Wunsch von Wissenschaft, Industrie und Regierung. Das DLR-Institut für Hochfrequenztechnik und Radarsysteme ist der direkte Nachfolger dieser Einrichtung.
Die Entwicklung und den Weg vom FFO zum heutigen IHR wird von Herrn Dr. Wolfgang Keydel an Beispielen wichtiger Aktivitäten und Epoche machender Ergebnisse aus den vergangenen 70 Jahren skizzieren, z.B. kalibrierte Rückstreumessungen an Flugzeugmodellen mit cm-Wellen (1940), die Erfindung des Halbleitertransistors durch Welker (1945), Entwurf und Systemführung beim Aufbau der Zentralen Deutschen Bodenstation (ZDBS) bei Weilheim (Beginn 1967), Entwicklung eines der ersten europäischen GPS-Empfängers (1982). Die Beteiligung an 5 Space - Shuttle – Missionen etc. Im Anschluss an die Erwähnung der aktuellen, deutschen Satellitenmissionen SAR-Lupe und TerraSAR wird TanDEM-X als zukünftiges Projekt abschließend Erwähnung finden.
Mehr
Francesco De Zan "Three-Dimensional Phase Unwrapping Formulation, Two-Step Approximations and Examples"
Dienstag, 20. November 2007
15:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
The problem of phase unwrapping for multitemporal SAR datasets is naturally a three-dimensional problem, where space and time should be used together. The simplest complete 3D formulation can be given in terms of a linear system of double-differences (one in space and one in time). For practical implementations, the choice of the equations to include is critical, in a typical trade-off between reliability and redundancy. Two-step solutions (e.g. 2D+1D) and iterative solutions are introduced, the latter is meant to retain some of the benefits of the complete 3D system. The careful choice of the equations can spare us to model the relative displacement of connected points and yields improved unwrapped time-series. This work is intended for displacements characterized by changing velocity, in particular for systems with frequent revisit.
Rudolf Schmid "Max Dieckmann - Gründer des Forschungs-Standorts Oberpfaffenhofen"
Dienstag, 6. November 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Vor 70 Jahren, im Jahr 1937, gründete Prof. Max Dieckmann das „Flugfunkforschungsinstitut Oberpfaffenhofen“ (FFO) als selbständige Forschungseinrichtung. Aus dieser Einrichtung entwickelte sich das heutige Forschungszentrum des DLR in Oberpfaffenhofen.
Herr Rudolf Schmid wird die Persönlichkeit von Prof. Max Dieckmann und seine Bedeutung für Wissenschaft und Forschung vorstellen.
Max Dieckmann wurde 1882 in Hermannsacker bei Stollberg im Harz geboren. Nach dem Abitur in Leipzig studierte er Mathematik, Chemie, Experimentalphysik und allgemeine Elektrotechnik in Göttingen und Leipzig. Er beschäftigte sich dann an der Technischen Hochschule München mit der Praxis der luftelektrischen Messungen. 1905 ging Dieckmann an die Kaiser-Wilhelms-Universität nach Straßburg zu Ferdinand von Braun, der sich dort mit drahtloser Telegraphie beschäftigte. Bei ihm promovierte Max Dieckmann im Jahr 1907 mit einer hochfrequenztechnischen Arbeit. Als Assistent an der Technischen Hochschule München pachtete er 1908 in Eigeninitiative in Gräfelfing eine Wiese und gründete dort die Drahtlostelegraphischen und Luftelektrischen Versuchsstation Gräfelfing (DVG). In einer kleinen Holzhütte begann er dort luftelektrische Messungen auszuführen. Als außerordentlicher Professor mit Lehrauftrag bezog er seine Gräfelfinger Station erfolgreich in den Lehr- und Forschungsbetrieb ein. Im Jahr 1936 wurde er zum planmäßigen außerordentlichen Professor an der TH München ernannt; zugleich wurde dort für ihn das Institut für Radiotechnik und Flugfunkwesen eingerichtet. 1937 baute er das Flugfunk-Forschungsinstitut Oberpfaffenhofen auf und war bis 1944 dessen Direktor. Max Dieckmann starb am 28. Juli 1960 in Gräfelfing.
Mehr
Rafael Zandona Schneider "Last Developments of Polarimetric Properties in Coherent Scatters (CS´s)"
Dienstag, 23. Oktober 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Recently, the Coherent Scatterers (CSs) technique, which allows the detection of point-like scatterers with a reduced number of SAR images, has been proposed. In contradiction to the randomly nature of distributed scatterers, such CSs are deterministic scatterers, being hence polarimetric coherent, characterized by high polarimetric and interferometric coherence, having several potential applications in fields of polarimetry, interferometry, polarimetric interferometry, polarimetric and radiometric image calibration, Faraday rotation correction, etc.
In this work, the last developments concerning polarimetric aspects of CSs are presented. The presentation involves mainly three topics:
-LOS rotation angle
-Scattering matrix parameterization in terms of scatterer symmetry degrees
-Polarimetric aspects in Differential Interferometry
LOS rotation angle:
An important parameter of interest when aiming scatterers information extraction, scatterer movement, etc., and that can be determined by exploiting polarimetry, is the scatterer rotation angle about the Line Of Sight (LOS) radar direction. Several approaches for that purpose have been in the far or near past proposed. We show that the approaches which can be consistently applied for general asymmetric scatterers can be divided into two main classes that are fundamentally different:
- Rotation Transformation Based Routines (RTBR) and
- Consimilarity Transformation Based Routines (CTBR),
and we present their fundamental difference. Many different proposed procedures are in fact equivalent falling into one of these two classes. The concept of the underlying scatterer signature of RTBR and CTBR is not the same, and although in many cases they converge to the same LOS rotation estimation, this is not true for general asymmetric scatterers.
Scattering matrix parameterization in terms of scatterer symmetry degrees:
Using the CTBR structure, an alternative parameterization of the scattering matrix is proposed, which is based on Line Of Sight symmetries of the corresponding scatterer. Namely, we decompose the portion of the scattering matrix which is related to the scatterer intrinsic scattering mechanism into three contributions: rotation symmetry, reflection symmetry, and a characteristic internal phase. Using such parameterization, better phenomenological insights on the nature of the scatterers can be done. The decomposition is applied on CSs detected using E-SAR images at L-band of the Munich city in Germany, where we demonstrate that CSs (and hence point-like scatterers) are not necessarily symmetric scatterers.
Polarimetric aspects in D-InSAR:
Finally, we investigate the impact of polarimetry and polarimetric effects on the Differential SAR Interferometry (DinSAR) technique for the coherent backscattering reciprocal case, with the aim to obtain better accuracy, to obtain further information about the scatterer movement, and to extract additional scatterer structure information. Emphasis is given to the influences of Faraday and scatterer Line-of-Sight (LOS) rotations, and to the determination of the intrinsic scatterer scattering mechanism. It is demonstrated that such effects may bias the DinSAR phase estimation and that, when fully polarimetric data are available, such biases can be compensated.
Carlos Lopez Martinez "Theoretical and Experimental Research Activities at UPC in Radar Remote Sensing"
Dienstag, 09. Oktober 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
The objective of the talk is to present some of the Remote Sensing Lab's research activities of the Universitat Politècnica de Catalunya UPC in the field of Active Remote Sensing, covering from theoretical aspects to experimental work. In the former case, the research in multidimensional speckle noise modelling and filtering shall be briefly discussed. On the later, the different experiences conducted with the UPC-owned Ground-Based SAR sensor shall be introduced, especially in the frame of differential SAR interferometry DInSAR and polarimetric analyses on urban environments.
Rolf Scheiber "P-Band Sounder: Clutter Cancelation Techniques"
Dienstag, 02. Oktober 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
During the last 2 decades polar research could benefit from a series of radar sounding experiments conducted from ground or with aircrafts, mainly performed on Antarctica and Greenland. The main problem to be considered in the airborne case but even more essential in the space-borne case is the presence of clutter (off-nadir signals). It superimposes the nadir signal of interest, which is the reflection of the radar wave from different layers within the ice and from the bedrock. Doppler filtering and more recently also focused SAR and Doppler-delay processing were used to improve the Signal-to-Clutter Ratio (SCR) in along track direction. However, for higher altitude platforms and in the space-borne case cross-track clutter can completely mask out the signal of interest coming from the nadir direction. The present contribution focuses on two different techniques presently under investigation in the frame of the ACRAS study of ESA: Multiple phase center antennas are investigated with respect to their clutter suppression potential. To overcome the symmetry assumptions of two phase center antennas (like e.g. on MARSIS) multiple phase centers (at least 3) as proposed by ESA are used for this investigation. Repeat-pass techniques: Two techniques are investigated dealing with data acquired on multiple repeated orbits: Off-nadir data are used to retrieve the volumetric backscattering via tomographic SAR techniques. Nadir looking combinations of repeated orbits are analysed for dedicated retrieval of only the signal of interest, removing the clutter contribution. Implementation aspects for space-based terrestrial and extra-terrestrial ice sounding options are discussed.
Ernst Weissbrodt "Investigation of the Influence of Multi-Path Propagation on the Performance of the TanDEM-X Synchronization Link"
Dienstag, 25. September 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
One of the key issues of bi-static SAR (Synthetic Aperture Radar) is the phase noise of the oscillators involved, which dictate the performance of the entire system. For TanDEM-X a dedicated synchronization link is used to exchange pulses between the TerraSAR-X and the TanDEM-X satellites. The information extracted from these pulses is used to compensate the phase noise of the two oscillators. The aim of this Diplomarbeit was to investigate various factors influencing the performance of the synchronization link, such as multi-path effects due to reflections on parts of the satellites or shadowing and interference by obstacles in the near-field of the synchronization antennas. The investigation involved the modelling of the geometric conditions due to the Helix-Orbit and the embedding of these geometric conditions into a Multi-Path-Propagation Simulator. The results of this Simulator, together with synchronization horn measurement-data were used to estimate the performance of the TanDEM-X Synchronization Link.
Dr.-Ing. Rakesh Mohan Jha "Computational Electromagnetics (CEM) for Aerospace Applications & An Overview of the CEM Lab. of National Aerospace Laboratories (NAL) Bangalore India"
Dienstag, 18. September 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
The Computational Electromagnetics Lab. (CEM Lab.) of NAL Bangalore, India was founded in 1993. Our active areas of research include:
• Ray Tracing and Surface Modeling
• EM analysis for airborne antennas (for satellites and aircraft)
• EM design and analysis of Radomes (for aircraft, and on ground)
• Radar cross section (RCS) studies and RCS reduction
• Radar Absorbing Materials (RAM) and Structures (RAS)
• EM Characterization of Materials
Following the brief description of our activities, the Geodesic Constant Method (GCM) as an effective tool in computational electromagnetics (CEM) for aerospace applications will be emphasized. The GCM is a well-known 3-Dim analytical ray tracing technique developed by this speaker along with his host researcher (Prof. Dr.-Ing. Werner Wiesbeck), in Germany.
The popularity and viability of the GCM method for three inter-related areas of EM scattering and diffraction problems (far-field pattern, mutual coupling and RCS) will be explained qualitatively along with a surface modeling paradigm for realistic aerospace structures.
Besides these, other aerospace applications such as radome, where the CEM Lab. NAL has created a niche for itself, will be highlighted from the ray tracing perspective.
Finally, the emphasis of the CEM Lab. on putting equal weightage on theory, computational validation and measurements in the context of open domain, futuristic research for aerospace engineering applications will be highlighted.
Esra Erten "Scale-Based Texture Tracking with the Aim of Robust Glacier Surface Monitoring"
Dienstag, 18. September 2007
11:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Ludovic Villard "Modelling and Analysis of SAR Observables in Bistatic Configuration: Applications in Remote Sensing"
Dienstag, 12. Juni 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Spaceborne and airborne radar remote sensing missions are essential for both civilian and military applications. Until now, many monostatic experiments have been conducted, given us a better understanding of the SAR observables behavior and are needed for the development of inversion process. However, some scientific questions are still not solved and remain open that's why model simulations are needed. Especially, in the domain of the bistatic or multistatic SAR case for which a few experimental data are available and the involved scattering mechanisms are expected to change. Therefore, our objective is to assess the bistatic configuration contribution to identify the sensitive mechanisms, then validate our approach regarding experimental data and turn this to a simpler inversion process. In the presentation the electromagnetic forest model developed at ONERA will be described and some sensitivity analysis presented. At the end an outlook to the work during the one year stay at DLR will be given.
Angelo Coscia "Estimation of Temperate Forest Extinction with Pol-InSAR in X- and L-Band"
Dienstag, 22. Mai 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Martina Gabele "Moving Target Motion Parameter Estimation in Two-Channel SAR-GMTI"
Dienstag, 08. Mai 2007
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Part 1: Two-channel SAR-GMTI systems are suboptimal for moving target motion parameter estimation. Indeed, the ATI phase estimate of a moving target across-track velocity component is biased to lower values depending on the target signal to clutter ratio and the target across-track velocity. Additional antenna diversity can introduce additional degrees of freedom that can eliminate the bias problem. Aperture Switching is an accepted method to virtually increase the number of channels without adding new hardware. Additional phase centres can also be generated from already recorded two-channel SAR data by delaying and combining the recorded two-channel measurements. The combination operation manifests not only a third phase centre halfway between the phase centres of the two-channel system, but also a different antenna length of the virtual third antenna. This three-phase-centre system is then used for DPCA-ATI processing and three-pulse-canceller processing in order to estimate the target motion. The performance is compared to ATI from the original two-channel mode using simulations and real data.
Part 2: In an along-track interferometric SAR system, the discrete sampling of moving target signals can give rise to two types of ambiguity: Doppler ambiguity, and interferometric angle ambiguity. These ambiguities lead to ambiguities in target velocity estimation. Range cell migration of moving targets is unambiguous in target velocity. Hence, it can be used for resolving the ambiguities in target velocity estimation mentioned above. The wave number domain algorithm as well as the chirp scaling algorithm is adapted to moving target signals. In order to focus moving target signals with arbitrary velocities both approaches are extended to arbitrary Doppler frequency ands. Moving target signals distributed over two neighbouring parts appear at different positions in the SAR image and have different ATI phases. They show up as two weaker targets since the energy is split between them. It is demonstrated how the two targets can be identified as possibly the same target, and how they can be properly focussed by adaptation of the SAR focussing algorithms.
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