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Vorträge im Institutsseminar 2013
Martin Maier "Qualitätsmanagement bei HR - Aktueller Stand und weitere Planung"
Dienstag, 10. Dezember 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Der Vorstand des DLRs hat beschlossen, dass alle Institute und Einrichtungen bis Ende 2013 ein zertifizierungsfähiges Qualitätsmanagementsystem eingeführt haben sollen. Die Einführung eines Qualitätsmanagementssystems (QMS) in einem Forschungsinstitut erfordert ein anderes Vorgehen als bei einem Industrieunternehmen. Die Herausforderung bei der Einführung des QMS bei HR besteht im Spannungsfeld zwischen kreativer Forschung und der Schaffung von einheitlichen Prozessen und Vorgehensweisen. Grundsätzlich dient ein QMS nicht zum Selbstzweck sondern zur Unterstützung der wissenschaftlichen Arbeit. Um dieses Ziel zu erreichen, wurden im ersten Schritt alle Führungs- und Unterstützungsprozesse (z. B. Management von Drittmittelprojekten) erfasst und beschrieben. Dieser erste Schritt stellt die Basis für die Beschreibung der eigentlichen Kernprozesse (Forschen, Entwickeln, Beraten) dar. Im Seminar werden die beschriebenen Prozesse dargestellt und ein Ausblick auf die Einbindung der Kernprozesse gegeben.
Keith Morrison "Virtual-Bandwidth SAR (VB-SAR) For Sub-Surface Imaging"
Dienstag, 03. Dezember 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The goal of carrying out sub-surface imaging from space or aircraft has so far remained elusive. In response, a description is offered here of a novel new imaging technique. Virtual-bandwidth SAR (VB-SAR) promises to deliver a previously unachievable high-resolution, sub-surface imaging capability from large stand-off distances applicable to airborne and spaceborne platforms. This is in sharp contrast to current techniques, where discrimination relies on close-proximity measurement of the scene, usually with a ground-based system using large bandwidths. The earlier SubSAR scheme previously presented at DLR separated surface and sub-surface features based on their differing temporal DInSAR histories, providing a ‘yes/no’ discrimination, and possibly depth indication. VB-SAR imaging extends this to full 3D sub-surface imaging. The speed of the radar wave passing through the soil varies directly in response to variations in the dielectric of the soil medium, brought about by changes in the soil moisture. This can equivalently be treated as a change in the radar frequency. In this way, the real frequency of the illuminating SAR can be translated across a set of virtual frequencies, each corresponding to a moisture value present over a temporal sequence of measurements. For even modest changes in moisture of a few percent, the generated virtual bandwidth provides centimetric sub-surface vertical resolution.
Adithya Madanahalli "Investigation Of OFDM Signals For Imaging Radar Applications"
Dienstag, 19. November 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Spaceborne Synthetic Aperture Radar (SAR) is a well established remote sensing technique that is being used for earth observation and monitoring for more than three decades. State-of-the-art systems have inherent system limitations which make them incapable of achieving the future vision of round the clock global monitoring. This has initiated research on new methods which use multiple transmit/receive channels (MIMO) and digital beamforming (DBF) techniques to overcome these problems in future SAR systems. It is found that waveform design in case of a MIMO-SAR system plays a critical role in determining the system performance. The use of OFDM Chirp waveforms is one of the several alternatives which have been deemed to satisfy all the requirements for a MIMO-SAR system. In this work the ability of these OFDM Chirp waveforms for spaceborne SAR applications are investigated. The algorithm is established and the parameters affecting system design are determined. Further the performance of the algorithm is analyzed theoretically using estimation theory and ambiguity function analysis. A radar system simulator which simulates the use of OFDM Chirp waveforms for imaging applications is developed. Finally, experiments are performed using the MIMO Radar Demonstrator to verify theoretical as well as simulation results.
Noora Al-Kahachi "Polarimetric SAR Modelling of a Two-Layer Structure - A Case Study Based on Subarctic Lakes"
Dienstag, 05. November 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The work contributes to the interpretation of quad polarimetric SAR data over (shallow) subarctic lakes, on the purpose of investigating SAR capabilities in revealing facts about the subsurface and the inhomogeneities within the ice layer which are dominated mainly by methane bubbles. For this, a model for the polarimetric backscattering from a two-layer structure observed by a fully polarimetric side looking synthetic aperture radar at low frequency (L-Band) is developed. The upper layer thickness is few metres thick and contains inhomogeneities. The developed model describes the backscattering as the incoherent sum of the three main contributions: subsurface (X-Bragg), volume and dihedral backscattering. The volume is modelled as a cloud of partially vertically oriented ellipsoids. The dihedral backscattering component is modelled as the reflected electromagnetic wave on the subsurface after being scattered by the same cloud of particles that is responsible for the volume backscattering. The mathematical formulation of this dihedral backscattering is presented for the first time here and proved to be an essential component in the model. The model simulations are compared to data obtained by ALOS-PALSAR over frozen shallow subarctic lakes acquired over several regions in the northern wetlands. ALOS data show the same polarimetric backscattered signature as the simulations. The model can describe temporal changes of the ice and the difference between grounded and floating ice.
Gerard Marull Paretas "Development of a multi-channel SAR simulator for open-oceans: OASIS"
Freitag, 25. Oktober 2013
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Interest in application of remote sensing to the ocean by microwave radars started in the decade of the sixties. Major applications are the measurement of surface winds from absolute backscattered power and the interpretation of relative intensity variations in radar images due to the presence of long waves, current gradients, surface films, or atmospheric effects. During this period important efforts were put to both the making of measurements and the development of theoretical models to understand the electromagnetic (EM) interaction with the oceans. The first SAR application to oceans was carried out by the first civilian SAR, Seasat, in 1978. It was an L-band SAR and it provided the first high resolution radar images of the ocean from space. More recently, interest in ocean applications has come again into the scene for the measurement of surface currents by using Along-Track Interferometry (ATI-SAR). The work of this master thesis has focused on the development of a multi-channel SAR simulator for open-oceans called OASIS. It is completely written in Python and uses a parallel algorithm to speed up the simulations. The approach taken by OASIS is to first generate an ocean surface by using empirical or semi-empirical spectrum models. Then, for each time-step and grid-point, the complex backscattering coefficient is computed following the surface geometry. This approach allows to simulate the radar return of time-evolving surfaces. OASIS if a full-featured simulator, and thus it generates the uncompressed SAR range-profiles (raw data), it processes the raw data and it performs ATI analysis.
Björn Döring "Learning from the field of photometry: The way towards better radiometric measurements"
Dienstag, 08. Oktober 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The principle of synthetic aperture radar (SAR) was invented 60 years ago. Since then, the technique has immensely evolved and is now widely used not only for target detection, but also for target estimation in numerous parameter inversion problems. Although soil moisture and biomass estimation algorithms, for instance, require radiometrically calibrated data, measurement traceability is still not established for any SAR system known to the authors. The quantitative comparability of data products acquired with different settings or by different sensors is therefore not guaranteed. This presentation addresses two problems which need to be solved before traceable measurements can be established: - At the moment, radar cross section (RCS) is wrongly used as the radiometric measurement quantity for point targets. RCS is a body property depending on frequency and incidence angle. The pixel brightness in a SAR image, on the other hand, depends on the measured complex amplitudes and the weighted averaging (over the pulse bandwidth and the azimuth angles) executed by the SAR processor. To overcome the problem, we propose to report a target’s equivalent radar cross section (ERCS) instead of its RCS. The ERCS shall be equal to the radar cross section of a perfectly conducting sphere which would result in an equivalent pixel intensity if the sphere were to replace the measured target. This definition exploits the independence of a (large) sphere’s backscatter with respect to frequency and (monostatic) incidence angle. The current absolute radiometric calibration approach needs to be adapted accordingly. - Up to now, the influence of apodization functions (like the Hamming window) on radiometric measurements has been neglected. In cases where the frequency and angular dependence of a target’s backscatter is relevant (i.e. especially for high-resolution SAR systems), radiometric measurements become incomparable if different apodization functions are used during processing. As a practical solution we propose to introduce a set of standardized apodization functions, which shall be used across SAR systems. Only then do SAR images become directly comparable. In the presentation, parallels will be drawn to the field of photometry in astronomy. In photometry, the intensity of an astronomical object's radiation is measured. In the first half of the last century, measurement passbands (frequency bands) were defined “by chance” through the physical properties of used photographic films, lenses, and so on. In the second half of the last century, more accurate measurements became possible, and standard passbands were developed to allow comparable, repeatable measurements while fully embracing the frequency dependent characteristics of the measurement equipment and calibration objects. This is very well comparable to the current situation in SAR described above, where the definition of ERCS acknowledges the general spectral (and angular) backscatter dependence and standardized apodization functions take up the role of standardized optical filters. We believe that a discussion of current radiometric measurement praxis is necessary and a prerequisite for higher quality, comparable measurements with low to very high resolution SAR systems. The introduction of equivalent radar cross section as the new measurement quantity and of standardized apodization functions is an important first step in this direction.
Tobias Rommel "An Orthogonal Waveform For MIMO-SAR Applications"
Dienstag, 01. Oktober 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Next generation spaceborne Synthetic Aperture Radars (SAR) have to meet higher requirements for spatial and radiometric resolution, as well as coverage. This is due to the success of current SAR systems, and the manifold users demanding for a steady evolution of the SAR technology to satisfy increasing performance requirements. A review of several ongoing studies shows that a promising candidate for the next generation SAR is a multi-channel radar utilizing Multiple-Input Multiple-Output channels (MIMO) in combination with Digital Beamforming (DBF). These systems offer higher operational flexibility and improved performance compared to conventional radar systems using analog beam steering. DBF on receive, in particular, overcomes the fundamental resolution-coverage limitation of classical SAR systems and can deliver high resolution and simultaneously wide swath images. With pattern synthesis and Null-steering techniques it’s even possible to suppress spatial interferences and signal ambiguities. As a further example, dual transmit channels can be used for coherent full polarimetric acquisitions without increase of the pulse repetition frequency. However, multiple transmit channels, which transmit simultaneously in the same frequency band provide currently a challenge. With conventional methods it becomes impossible to find a modulation or multiplex technique which is applicable for observing large landscapes with high resolution. Therefore in this presentation a modified Chirp-Waveform called “Short-Term Shift-Orthogonal Waveform” is introduced which provides perfect orthogonality for surface scatterers by extension of the common ambiguity function by an additional degree of freedom with the use of DBF techniques. The results are the first step towards future spaceborne multimodal radar systems using orthogonal waveforms and reflector-based DBF antennas. At our institute a prototype of the future radar systems has been developed to verify such innovative modes. The system architecture of the MIMO Radar Demonstrator and recent measurement results obtained with a DBF reflector antenna will also be presented. The seminar concludes with a summary of ongoing studies in this field.
Jun Su Kim "Development of Ionosphere Estimation Techniques for the Correction of SAR data"
Dienstag, 24. September 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Low frequency synthetic aperture radar (SAR) configurations play an important role in mon-itoring forests and ice sheets on global scales. They provide the ability to image systematic large areas at high spatial and temporal resolution, while at the same time they allow to penetrate into the forest and ice volume providing information about the vertical structure of such media. However, at lower frequencies spaceborne SAR measurements are affected by the presence of the ionosphere, i.e., a dispersive, anisotropic and spatial as well as temporal inhomogeneous partial plasma, located in the upper part of Earth's atmosphere. The ionospheric layer is characterised by an anisotropic (spatial and/or temporal) variation of the refractive index that affects intensity, polarisation as well as (phase and group) velocity of the transmitted and received SAR pulses passing through. In consequence, the amplitude and phase of the finally obtained (complex) SAR images are distorted impacting intensity, polarimetric and interferometric SAR measurements. The ionosphere can be characterised in terms of the Total Electron Content (TEC), which stands for the integrated number density of the free electrons along the propagation path. A consistent theoretical framework, required for describing the ionospheric impact (by means of TEC) on intensity, polarimetric and interferometric SAR observables, has been established in this thesis that allows to reveal the interconnection between the ionospheric impact on the individual elements of different SAR observation spaces. A variety of techniques have been developed and proposed to compensate the effects, induced by the ionosphere by estimating the distortion on a single SAR image parameter (e.g. focus, contrast, geometry, or polarimetric signature) and correcting the associated SAR observable. Common to all these techniques is the fact that only the ionospheric distortion on a (small) subset of the available observation space is considered, while the remainder of the redundant and synergetic information is ignored. As a result, the achieved performance depends strongly on the ionosperic conditions as well as on the SAR system parameters. In this thesis an innovative integrated ionospheric compensation approach, that maximizes the exploited information, has been developed. An accurate high (spatial) resolution TEC map is obtained by combining the distortion estimates of a larger set of conventional, polarimetric and/or interferometric image parameters that is then used to compensate the ionospheric impact with in-creased accuracy and robustness across the whole observation space. This leads to optimized correc-tion results for a wide range of ionospheric conditions (including scintillations) and SAR system parameters. The proposed methodology has been implemented and assessed by means of a large set of single image or interferometric quad-polarimetric ALOS-PALSAR data and simulated BIOMASS P-band data covering a wide range of ionospheric conditions. The achieved performance is critically analysed and discussed in terms of ionospheric conditions and system or data parameters and then projected on different spaceborne SAR scenarios.
Maria Sanjuan-Ferrer "Detection of Coherent Scatterers in SAR Data: Algorithms and Applications"
Freitag, 20. September 2013
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The inherent properties of SAR offers a great potential for Earth observation and monitoring applications in both urban and natural environments. Due to the limited spatial resolution of the first generation of SAR data, the size of the image resolution cells is often much larger than the used wavelengths. Consequently, in combination with the intrinsic complexity of the scattering scenarios, several elementary scatterers are normally present inside a single resolution cell, and constructive and destructive interferences of the fields backscattered by the individual scatterers are expected. However, with the increase of the spatial resolution in modern SAR systems, situations in which only few scatterers or even just one single dominant scatterer is present inside the resolution cell have become more habitual, changing the SAR data statistics. In these cases, the scattering characteristics of the cell can be considered then quasi-deterministic with a backscattered constant energy in time and frequency and a well-defined phase and amplitude behavior. Such scatterers can be used for a wide range of applications as, for instance, coregistration, calibration or information extraction. In this work, the identification, detection, characterization and potential applications of the so-called coherent scatterers (CS's) is addressed in detail. By definition, a CS is a quasi-deterministic scatterer whose response does not decorrelate in the range and/or azimuth frequency bandwidth, being characterized by a high spectral correlation, and it is normally embedded in clutter. Exploiting the spectral correlation property, a novel CS detection approach based on the generalized likelihood ratio test (GLRTA) has been proposed, which possesses some advantages in comparison with the classical CS detection methods. After a complete theoretical performance analysis, the selected CS detection methods are tested on real data using TerraSAR-X images over different environments, considering both urban and natural scenes. The wide range of scenarios is used for a more clear comprehension of the detection capabilities together with a characterization of CS's as a function of the scene features. Finally, the availability of time series data is exploited to get first insights of possible applications.
Maurizio Caputo "Soil Moisture Retrieval under a Changing Vegetation Cover Using Dual-Polarimetric Data at X-Band"
Dienstag, 10. September 2013
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Soil moisture retrieval under vegetation cover plays an important role in the hydrological cycle steering the soil boundary interactions between hydrosphere, biosphere and atmosphere. Furthermore, it is a key limiting factor in agriculture production for semi-arid and arid regions. In this master thesis the sensing of soil moisture is performed by means of Synthetic Aperture Radar (SAR) because of the distinct sensitivity to the dielectric properties of the soil. Since an enormous amount of X-band dual-polarimetric coherent data got available with the successful launch of TerraSAR-X/TanDEM-X, the retrieval of soil moisture by exploiting this dual-polarimetric observation space is of great interest. In order to describe the agricultural scattering scenario, the IEM model is chosen appropriate for soil scattering on ground at X-band. However, vegetation cover biases the soil moisture inversion during the vegetation growth cycle and must be removed before inversion of soil moisture. Hence, a vegetation particle scattering model, adaptable to a variety of agricultural crop types, is implemented for characterization of the vegetation scattering. Therefore, the estimation of the vegetation scattering intensity is necessary, which mainly depends on the cross-polarization channel. In this work, a synthesis of the cross-polarization is adopted by applying the model of Souyris et al. assuming azimuthal symmetry. From multi-frequency (L, C, X), time series analyses of fully polarimetric data, it results that the assumption of azimuthal symmetry is best met at X-band, especially for agricultural areas compared to urban and forested areas. Using the synthesized cross-polarization, polarimetric model-based decomposition techniques, that enable the separation of the vegetation and ground scattering contributions, have been developed incorporating different kinds of vegetation scattering types. Five vegetation volumes have been investigated during the analyses representing the main vegetation geometries in agriculture. After removal of the vegetation scattering, the remaining ground component is inverted using the IEM scattering model. Comparing the estimated soil moisture values with in situ measurement from the Demmin region in northern Germany (near Berlin), collected by research colleagues of the GFZ Potsdam, the applied vegetation decomposition types exhibit different inversion results concerning the inversion rate. Hence, about 40-60% of the agricultural area can be inverted at the beginning and at the end of the vegetation cycle, and about 10-40% in the middle of the vegetation cycle, due to the dominance of the vegetation scattering during high vegetation cover in late spring/early summer. Moreover, fields of different crop types can be inverted best with different kinds of polarimetric decompositions. Therefore, the quality of the estimated moisture values with just one decomposition type is heterogeneous (RMSE-range: 5-13vol.%) along the vegetation growing cycle. In order to describe the variety of crops, one type of vegetation volume description is therefore not enough and an a priori vegetation type selection will be implemented in a next research step.
Virginia Brancato "Electromagnetic Modelling of P-band Pol-SAR Signatures of a Polythermal Ice-cap"
Dienstag, 03. September 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Glaciers and ice sheets are extremely complex components of our planet’s ecosystem, playing a pivotal role in the global water cycle. As a consequence of the ongoing climate change, the need of continuous cryospheric observations on a global scale has increased the interest in using Synthetic Aperture Radar (SAR) due to its high resolution and wide coverage capabilities. Moreover, at long wavelengths (e.g. L- and P-band), the radar signal can penetrate several meters deep into the glaciers, providing the possibility to extract information about their subsurface structure. Fully polarimetric P-band data collected over the Austfonna ice-cap, in Svalbard, Norway, by DLR’s E-SAR system within the SVALEX 2005 and ICESAR 2007 campaigns have been employed in this study. In particular, two test sites located in different facies of the ice cap have been considered. The results of a polarimetric analysis performed on a set of descriptors (including polarimetric ratios, phase differences, entropy and alpha angle), suggest the presence of dominant volume scattering in each test site, even though with different characteristics. An existing polarimetric model for volume scattering has been adopted in order to provide a physical interpretation of the observed signatures. The glacier subsurface is considered as a dielectric medium (background) rich of inclusions (e.g. ice lenses, glands, air bubbles) assumed to be responsible for the volume scattering. The shape and orientation of the inclusions appear to be the most influent parameters, allowing the model to cover a variety of polarimetric behaviors. Moreover, differential propagation effects occurring in presence of anisotropic media (e.g. oriented volume) are included to attempt to explain polarization phase differences. Finally, the effect of the incidence angle is also considered. With the support of a set of ground measurements, the model has been set up differently for the two test sites, according to the different subsurface structures, and an interpretation of the polarimetric signatures observed in the SAR data is suggested. Finally, the availability of multi-temporal acquisitions allows the analysis and a preliminary interpretation of the observed temporal variations.
Rafaela Lopes Melo "Digital Beamforming Techniques applied to reflector-based SAR systems"
Dienstag, 16. Juli 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The future of SAR applications is faced towards the use of Digital Beamforming (DBF) techniques. DBF SAR systems spare the use of an analogous receiver hardware which is replaced by digital components. The digital combination of multiple channels underlies advanced radar operational modes overcoming coverage and resolution limitations inherent to conventional SAR. One of the most promising DBF SAR architectures uses a reflector antenna with a digital feed array. Reflector based DBF SAR has a potential to outperform planar array systems by offering better imaging characteristics and less hardware effort required for its realization. This seminar talk introduces a reflector-based DBF SAR system demonstrator and focuses on its antenna part and an experimental demonstration of DBF techniques applied to measurement data.
Andrea Cantini "3-D structure of a forest at L-band: experiments towards a spaceborne implementation"
Freitag, 12. Juli 2013
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Due to its ecological importance, the monitoring of the vertical structure of forests is continuously raising the interest of the synthetic aperture radar (SAR) scientific community. In particular, SAR tomography allows reconstructing the 3-D distribution of the radar power backscattered by a forest by combining more than two SAR acquisitions with baseline diversity. Beyond specific estimation algorithms, the link between the estimated tomograms (depending in general on frequency, polarization and acquisition geometry) and physical forest structure is essential for establishing potential applications. The main objective of this seminar is to present and discuss the results of some airborne tomographic experiments, considering forest stands with different biomass levels and different species composition. The analysis has been carried out by processing an L-band multibaseline fully polarimetric data set acquired over the temperate forest of Traunstein (Germany) by means of the DLR’s E-SAR platform, and by exploiting an auxiliary Lidar acquisition and a set of ground measurements. The effects of the weather conditions on the estimated profiles have been analyzed as well by processing data acquired after a dry and a rainy period. It is worth noting that the variability of the profiles with the environmental conditions can be seen as a critical aspect for the implementation of 3-D forest structure monitoring from space. For this reason, considering a single-pass interferometric implementation as proposed for the Tandem-L mission, the impact of the inhomogeneity of the interferometric coherences on structure estimation has been quantified.
Jan Eilers "Systemtechnik Simulation Framework"
Dienstag, 09. Juli 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The Systemtechnik Simulation Framework (S-SF) is a software suit, which contains an analysis tool set. The idea behind the S-SF is to describe one space related scenario and do the analysis in one environment. This is to avoid failures by using different software modules to analyze a scenario and to increase the speed of a study. The scenario contains definitions of different objects (targets, ground stations, satellites, sensors, subsystems, image products,…). For the celestial calculations like a satellite orbit, contact times or angles it is possible to choose between two engines. One is AGI-STK the other is VENI. AGI-STK is commercial software to model, analyze and visualize space, defense and intelligence systems with an interface for different program languages. VENI is in-house developed software to model and analyze space systems. A small subset from this toolbox is the mission analysis, mission planning and interferometry analysis for satellite constellations.
Werner Wiesbeck "Systemkonzepte für das Radar 2020"
Freitag, 05. Juli 2013
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Die Radartechnik ist inzwischen fast 110 Jahre für die unterschiedlichsten Aufgaben und Anwendungen eingesetzt worden. In dieser Zeit hat sich die Systemtechnik des Radars den Innovationszyklen der Technologie und des Bedarfs angepasst. Typische Beispiele waren das Pulsradar oder Phased Array, um nur zwei zu nennen. In den nächsten Jahren ist ein nahe zu revolutionärer Technologiesprung in der Radartechnik zu erwarten. Die erforderlichen und sich geradezu aufdrängenden Technologien resultieren weitgehend aus der Kommunikationstechnik. Sie werden in die Radarsystemtechnik einfließen und vollkommen neue Möglichkeiten eröffnen. Im Einzelnen sind die zu erwartenden Systemideen: - Intelligente Signalcodierung - MIMO Radar - Digitale Strahlformung - Array Imaging - Kombination Radar x Kommunikation = RadCom In dem Vortrag werden diese neuen Technologien von der Systemseite betrachtet und integriert. Durch diese neuen Systemtechnologien werden die Radare leistungsfähiger, flexibler und auch kostengünstiger werden. Ihre mögliche Anwendung erstreckt sich auf nahezu alle Bereiche der Radartechnik und erschließt zudem neue Anwendungen.
Michele Martone "Decorrelation Effects in Bistatic TanDEM-X Acquisitions"
Dienstag, 02. Juli 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The primary objective of the TanDEM-X mission is the generation of a worldwide and high-precision DEM in bistatic configuration. Both satellites fly in close formation of a few hundred meters distance and form an innovative and flexible single-pass radar interferometer, allowing for the acquisition of highly accurate cross- and along-track interferograms. The key parameter in estimating SAR interferometric performance is the coherence, which represents the normalized correlation coefficient between master and slave acquisition and gives information about the amount of noise in the interferogram. The influence of several decorrelation sources has been investigated by means of statistical analyses and dedicated acquisitions on defined test sites. This talk will mainly focus on the impact of signal-to-noise ratio (SNR), for example over deserts, volume decorrelation in forested areas, and raw data quantization dependence. These analyses have directly resulted in an optimization of the TanDEM-X global acquisition strategy and the achieved performance improvement is presented.
Harald Anglberger "The usage of SAR simulation for practical applications"
Dienstag, 18. Juni 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In the past few years a SAR simulator called SAREF has been developed in the institute mainly for the design of future high resolution SAR systems and for the analysis of existing ones. This end-to-end simulation chain makes it possible to study the impact on image quality by a variation of system parameters not only on point scatterers, but also on complex objects or small scenes. Initially, SAREF was specifically designed as a toolset for the expert radar scientist. Recently, the simulator has been made applicable for the actual user of SAR remote sensing data. This presentation will illustrate the major achievements by giving application examples for the simulator in the fields of signature analysis, user assisted object recognition, image acquisition planning and merging of optical and SAR data in the radar slant-range space.
Timo Kempf "Image fusion of different spaceborne SAR sensors for change detection and SAR-image enhancement by time-series exploitation"
Dienstag, 04. Juni 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Change detection by spaceborne high resolution synthetic aperture radar images is a very powerful tool for reconnaissance tasks, as this is largely uninfluenced by the weather and the time of the day and doesn’t violate sovereign rights. Use of different spaceborne SAR sensors would reduce the revisit time of an region of interest considerably allowing a denser monitoring. But the imaging of different sensors can differ in the frequency band, the resolution and the aspect angle, commonly leading to higher false-alarm rates in the change detection. Nevertheless, this presentation demonstrates a successful image fusion of Radarsat-2 and TerraSAR-X. Additionaly, it will be shown, how visual image analysis of spaceborne SAR-data can be supported by exploitation of time and aspect series and application of user-friendly filters.
Paola Rizzoli "Radar Backscatter Modelling with TanDEM-X Data"
Dienstag, 14. Mai 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Radar backscatter knowledge represents a valuable input for many remote sensing applications. The amount of data acquired within the TanDEM-X mission allows for the characterization of X-band backscatter on a global scale. A method for the characterization of radar backscatter behavior using a global statistical approach will be presented. A series of models can be derived, focusing on the backscatter dependency on polarization, local incidence angle, ground classification, and seasonal time. The developed approach for the algorithm’s verification is presented as well, together with some preliminary results obtained from TanDEM-X data. The generation of up to-date backscatter models for X-Band will provide a useful data base for the development of a large number of scientific applications and for the optimization of future radar systems.
Carolina Tienda Herrero "Reflectarray Antennas in Dual Reflector Configuration"
Dienstag, 07. Mai 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Recent work on dual-reflector antennas involving reflectarrays is reviewed. Both dual-reflector antenna with a reflectarray subreflector and dual-reflectarrays antennas with flat or parabolic main reflectarray are considered. First, a general analysis technique for these two configurations is described. Second, results for beam scanning and contoured-beam applications in different frequency bands are shown and discussed. The performance and capabilities of these antennas are shown by describing some practical design cases for radar, satellite communications and direct broadcast satellite (DBS) applications.
Ulrich Steinbrecher "WideScanSAR - ein neuer Aufnahmemode für TerraSAR-X"
Dienstag, 30. April 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Bald soll es für die TerraSAR-X Mission zwei neue Aufnahmemoden geben, Staring-Spotlight und Wide-ScanSAR. Hier werden das Design des Wide-ScanSAR Modes und erste Testaufnahmen präsentiert. Zu optimieren galt es die Steifenbreite in Abhängigkeit der klassischen SAR Parameter, Range Ambiguity Ratio, Azimuth Ambiguty Ratio und des Noise Equivalent Sigma Zero unter Berücksichtigung der Einschränkungen, die durch die TSX-1 und TDX-1 Satelliten gegeben sind. Durch Wechseln von festen zu variablen Beambreiten und der Minimierung von Reserven konnte ein Mode designed werden, der eine variable Streifenbreite von 200-250 km hat, ohne die Robustheit bzgl. Topografievariation zu verschlechtern.
Martina Gabele "Synthetic Aperture Radar / Ground Moving Target Indication for Spacebased Radar with Two-Dimensional Antenna Arrays"
Freitag, 26. April 2013
15.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic Aperture Radar / Ground Moving Target Indication (SAR / GMTI) is an active radar remote sensing technique, based on the coherent combination of SAR imaging and antenna array processing. The SAR / GMTI technique provided a step forward in quantitative ground motion parameter estimation. In the last two decades, airborne SAR / GMTI experiments, and in the last years also spaceborne SAR / GMTI experiments evaluated the potential of the SAR / GMTI techniques to estimate ground motion parameters (i.e. target position, velocity, and motion direction). This dissertation addresses the actual status, the potentials and limitations of spaceborne SAR / GMTI with single / monostatic platforms carrying two-dimensional antenna arrays. The SAR processing is applied in order to generate high resolution images of the target signals, antenna array processing in along-track direction is applied for GMTI and antenna array processing in across-track direction in order to cover large swathes. This trade-off between SAR imaging capability, GMTI capability and swath coverage requires a careful design of radar systems and operation modes. Therefore, one main goal of this dissertation is to provide new spaceborne radar system designs and operation modes which provide a good trade-off between GMTI capability and swath coverage, and furthermore a high flexibility in adjusting between SAR capability and GMTI capability. One considered future SAR system is Astrium’s High Resolution Wide Swath Reference System. Another system is a radar design which is characterized mainly by a largely increased beamsteering capability. Besides, one secondary objective of this dissertation were to extend the signal modeling for combining SAR imaging and antenna array processing in spaceborne geometries. Another secondary objective was to calibrate the first available spaceborne SAR / along-track array experimental data, namely the data from the TerraSAR-X dual receive antenna mode. Lastbut not least, another secondary objective of this dissertation was to demonstrate the validity of the signal and performance modeling by processing the data from airborne and spaceborne experimental campaigns.
Rolf Scheiber "Multi Phase Center Antenna Processing of Ice Sounding Radar Signals for Across Track Surface Clutter Cancellation"
Dienstag, 23. April 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
ESA’s POLarimetric Airborne Radar Ice Sounder demonstrator (POLARIS) – built, maintained and deployed by the Technical University of Denmark (DTU) - operates at P-band and features a multi-phase-center antenna for the purpose of surface clutter suppression. The first data suitable for the development and demonstration of surface clutter cancellation methods were acquired in February 2011 during the IceGrav campaign in Antarctica. The purpose of the present study was to investigate and compare different methods for surface clutter cancellation and to implement a Processing Tool to augment the along-track POLARIS processor developed by ESA, thus improving bedrock detectability. Four algorithms have been selected for implementation and analysis: the standard beamformer, two different clutter nulling algorithms and the optimum beamformer. Prior to the analysis with real POLARIS data the algorithms have been implemented in a simulation environment, allowing for a performance analysis concerning the different input parameters. These included pulse bandwidth, aircraft roll, cross-track terrain slopes, as well as POLARIS antenna patterns. The improved performance of the nulling and optimum beamformer techniques for surface clutter suppression compared to standard beamformer has been demonstrated and requirements on the knowledge of slope and roll parameters have been quantified. By means of simulation it was shown that the relatively large separation of the POLARIS phase centers (~lambda) is responsible for regions of high noise scaling around +/- 45deg off-nadir angle, which turned out to be annoying in particular for the application of the nulling techniques. The optimum beamformer instead is able to better handle these angular regions. The clutter suppression performance has also been demonstrated with the available POLARIS data from the IceGrav 2011 campaign. For all 4 available data takes a clear improvement in clutter suppression performance could be achieved, independent of the signal bandwidth. It was shown that, in terms of clutter suppression, the advanced methods (nulling and optimum beamformer) outperform the standard beamformer by up to 15 dB. However, it was also shown that a major limitation for the performance is the lack of a highly accurate ice surface model. For the purpose of this study it was necessary to rely on ASTER2 GDEM, as no Laser altimetry data from IceGrav were available in time.
Michelangelo Villano "Staggered-SAR: High-Resolution Wide-Swath Imaging by Continuous PRI Variation"
Dienstag, 16. April 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic aperture radar (SAR) is a remote sensing technique, capable of providing high resolution images independent of weather conditions and sunlight illumination. This makes SAR very attractive for the systematic observation of dynamic processes on the Earth’s surface. However, conventional SAR systems are limited, in that a wide swath can only be achieved at the expense of a degraded azimuth resolution. This limitation can be overcome by using systems with multiple receive apertures, displaced in along-track, but a very long antenna is required to map a wide swath. If a relatively short antenna with a single aperture in along-track is available, it is still possible to map a wide area using multiple elevation beams, but “blind ranges” are present across the swaths. Staggered-SAR is an innovative concept, based on the continuous variation of the pulse repetition interval (PRI), which allows high-resolution imaging of a wide continuous swath without the need for a long antenna with multiple apertures.
The presentation will introduce the Staggered-SAR concept and then focus on the design of PRI sequences, the pre-processing of the raw data and the resulting system performance.
Christopher Wecklich "DEM_Library: Generic DEM Access Library for IDL"
Dienstag, 09. April 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Correctly accessing Digital Elevation Models (DEM) can be a difficult challenge. Various DEMs exist, most of them with the corresponding Height Error Model (HEM) files, but some not. These DEM/HEM pairs contain various pixel sizes (in arcseconds), various height systems (Ellipsoid/Geoid), and various file sizes. To support the correct accessing of DEMs, the DEM Library IDL Object is a handy tool to access common DEMs and HEMs, for example, the SRTM. In addition to easy DEM data retrieval, this tool provides more sophisticated functions for SAR analysis, for example, a ray-intersection calculation function with the DEM surface. In this seminar, a general introduction to the DEM Library will be presented along with several examples demonstrating how the functions could be utilized. This will be followed with an introduction to the updates and new features in the last revision of the DEM Library. In order to better understand the overall DEM-Database, we will finish off with a review the various available DEMs therein, and finally review the two different height systems used in the DEM database.
Tilo Wiese "Potentielle Anwendungen moderner Inpainting-Algorithmen für die Verarbeitung von Höhenmodellen in der Fernerkundung"
Dienstag, 19. März 2013
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In der Fernerkundung spielen digitale Höhenmodelle eine wichtige Rolle. Sie werden auch in vielen weiteren Bereichen der Forschung und der Industrie für die Weiterverarbeitung und Herstellung von hoch genauen Produkten verwendet. Besonders in der Forschung ist man aber darauf bedacht, stets die höchstmögliche Qualität zur Verfügung zu haben, um weiterführende Ergebnisse bestmöglich umsetzen zu können. Was soll man aber machen, wenn das Testgebiet größere Ausmaße hat, als das zur Verfügung stehende hoch genaue Höhenmodell? Soll auf das niedriger aufgelöste Modell zurückgegriffen werden? Man kann Höhenmodelle unterschiedlicher Genauigkeit zusammenrechnen. Ein Problem stellt hierbei nur die Kante der unterschiedlichen Höhenmodelle dar, da dort ein Höhenversatz auftritt. Hier kann man mit klassischen Interpolations-Algorithmen Abhilfe schaffen und diese Bereiche miteinander verrechnen. Oder was soll man machen, wenn in der SAR-Interferometrie schlechte Kohärenz auftritt, man aber trotzdem ein bestmögliches Höhenmodell benötigt? Auch hier helfen Interpolationsalgorithmen. Ein moderner Ansatz kommt aus der digitalen Bildverarbeitung. Die sogenannten Inpainting-Verfahren benutzen umfassende Kanteninformationen, um den fehlerhaften Bereich im Bild zu rekonstruieren. Sie rekonstruieren Texturen, oder versuchen Linien gleicher Helligkeit zu vervollständigen. Im Laufe dieser Arbeit wird einer dieser Inpainting-Algorithmen näher vorgestellt und für die Verwendbarkeit in der Fernerkundung überprüft. Für eine generelle Verwendbarkeit werden Anpassungen an verschiedenen Parametern des Algorithmus vorgenommen, und es wird die Verwendung einer Bildpyramide umgesetzt. Um die Rekonstruktionseigenschaften zu überprüfen, werden direkte Vergleiche zwischen klassischen Interpolations-Algorithmen und dem gewählten Inpainting-Algorithmus basierend auf den unterschiedlichsten Datensätzen durchgeführt, um die Genauigkeit bei wechselnder Topographie zu untersuchen. Es werden weiterhin reale Beispiele durchgerechnet, um Qualitätsunterschiede zwischen den synthetischen Beispielen und der Realität auszuschließen, oder sichtbar zu machen. Zuletzt soll die Eignung auf zuvor erwähnte Fusion digitaler Höhenmodelle untersucht werden und in einem qualitativen Vergleich validiert werden.
Ali Eren Culhaoglu "Microwave Metamaterials: Superlensing and Design of Low Reflection Coatings"
Dienstag, 12. März 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Metamaterials are artificially engineered materials that have properties not attainable with naturally occurring materials, such as a negative refractive index. They enable the design of novel microwave devices, which cannot be realized on the basis of naturally occurring materials. The imaging properties of a metamaterial superlens and the design of metamaterial low reflection coatings are investigated in this work. A planar negative refractive index metamaterial slab focuses waves emitted from a Hertzian dipole to an image plane behind the slab. A resolution beyond that of conventional imaging systems is thereby achieved. The imaging characteristics of the superlens are investigated analytically in the spectral domain by expressing the fields as a Fourier integral. A novel approach for the realization of Drude and Lorentz dispersive metamaterial radar absorbers is presented. A metamaterial based anti-reflection coating is realized and studied experimentally.
Julia Stockamp "Multi-Frequency Analysis of Snow covered Areas using SAR Polarimetry"
Dienstag, 26. Februar 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Monitoring of Earth‘s snow reservoirs and their dynamic over time is increasingly important in the context of climate change. The large scale retrieval of snow parameters, such as snow water equivalent (SWE), can provide essential information about fresh water resources. In this multi-frequency analysis of C-band (quad-pol), X-band (dual-pol) and Ku-band (dual-pol) data of snow cover in Sodankylä, Finland, SWE is retrieved for a time series within the winter season 2011/2012. For that purpose, the CoReH2O forward model and inversion techniques are used. It is analyzed, how the different frequencies perform in a single frequency approach, and in particular, what C-band can contribute to a SWE inversion. By comparing dual-pol with quad-pol data, it is examined, whether there is an advantage of decomposing the total backscatter into volume and ground surface components and, subsequently, of using only the volume backscattering in the inversion process for SWE. The multi-frequency SAR data are complemented by ground measurements of SWE, snow depth and various meteorological and hydrological parameters for analysis and validation. Results show that in X-band the measured upward trend of SWE is partly reproduced in the dual-pol approach. It was found that C-band in dual-pol as well as quad-pol configuration performs unsatisfactorily in comparison to X-band for SWE retrieval. A polarimetric eigen-analysis of the quad-pol C-band data, however, reveals a significant correlation to the underlying soil and its freezing and thawing processes and not to snow cover. Hence, it is easily possible to establish a robust correlation between the polarimetric entropy/alpha values and the dielectric constant of the (snow covered) soil including the entire winter period.
Anita Pollner "DEM based shadow & layover detection using Python"
Dienstag, 29. Januar 2013
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The generation of Digital Elevation Models (DEMs) is one of the biggest applications for SAR interferometry. While SAR DEMs generally have highly accurate landscapes with high relief energy, they are subject to shadow/layover effects originating from the acquisition geometry. In the course of a 3-month internship, a software for the identification of shadow/layover areas based on reference DEMs was implemented. Python was chosen as the programming language for this software in order to gather first-hand experience.
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