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Vorträge im Institutsseminar 2016
Muriel Pinheiro "Multi-Mode SAR Interferometry for High-Precision DEM Generation"
Dienstag, 13. Dezember 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
SAR Interferometry (InSAR) is a well-established remote sensing technique widely employed for the retrieval of topographic information. The relative vertical accuracy of a Digital Elevation Model (DEM) generated through InSAR techniques depends, among other factors, on the spatial separation between master and slave sensors and on the signal correlation between both datasets. In monostatic single-pass configurations, master and slave data are acquired simultaneously by sensors mounted on the same platform. Consequently, the single-pass interferogram does not present temporal decorrelation and is less affected by spatially correlated artifacts. However, the fixed baseline limits the achievable relative vertical accuracy. On the other hand, repeat-pass configurations offer a flexible choice of baseline enabling the retrieval of very fine elevation measurements, provided that the temporal decorrelation can be kept small. Nevertheless, since the datasets are acquired independently, the interferograms are subject to artifacts due to, e.g., aircraft motion or propagation in the inhomogeneous atmosphere. Hence, the extraction of precise terrain information from repeat-pass data requires an accurate phase calibration, i.e., the removal of all undesired phase biases. In this thesis, the joint use of single- and repeat-pass datasets in a multi-mode configuration is proposed to profit from the stability of the single-pass derived DEMs in relation to spatially correlated artifacts, as well as from the robustness to noise associated with large baseline acquisitions. As the large-baseline interferometric phase is highly sensitive to the unknown topography and to systems errors and other artifacts, large phase variations between neighboring pixels are observed. The former in association with elevated noise can compromise the phase unwrapping, thus preventing the retrieval of accurate height measurements. In order to overcome this limitation and to promote a robust phase calibration, the use of data simultaneously acquired with an additional carrier frequency is proposed. Hence, the final DEM is extracted from a Dual-Frequency and Dual-Baseline (DFDB) dataset with the help of new algorithms developed for the proposed configuration. Specifically, a method for the mitigation of artifacts in the single-pass data due to multiple reflections in the aircraft is suggested. Furthermore, a dual-channel region-growing algorithm is proposed for efficient phase unwrapping. An active-contour-based unwrapping errors correction strategy is developed for the treatment of residual errors associated with challenging terrain characteristics. A DFDB framework is proposed for the calibration of residual constant and linear baseline errors and global phase offsets, including alternatives in the complex domain and considering the use of external reference data. Finally, the joint estimation of the underlying topographic information is discussed and the problem of the correction of spatially correlated artifacts in the repeat-pass data and noise reduction are tackled. All developed algorithms are validated with DFDB data acquired with the F-SAR sensor during two campaigns in Germany: the first over tidal flats in the Jade Bight, North Sea; and the second over a calibration test-site in Kaufbeuren. In both cases, the proposed methodology allows the generation of elevation models with relative and absolute vertical accuracies in the order of centimeters. Lastly, the developed phase unwrapping framework is applied to TanDEM-X large-baseline data, demonstrating the use of the algorithm for single-pass spaceborne datasets with multiple acquisitions.
Octavio Ponce "Multicircular Holographic SAR Tomography over Forested Areas"
Freitag, 2. Dezember 2016
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The understanding of the radar backscattering of vegetation is of significant interest to retrieve physical parameters in the biosphere, such as height, ground topography and extinction factor, and consequently to estimate biomass. In this respect, the CSAR and HoloSAR imaging modes are sensitive to volumetric scattering over 360°, thereby being able to fully characterise the objects of interest. The contribution of this investigation aims to investigate the full acquisition and processing chain of both modes, and consequently to obtain fully polarimetric 3-D images of forested areas. The three-dimensional impulse response function of CSAR and HoloSAR is discussed as a function of the acquisition geometry and radar properties. The proposed processing chain principally assumes distributed backscattering, and it is based on the fast factorised back-projection, as well as non-linear approaches such as compressive sensing and the generalised likelihood ratio test. Also phase calibration methods using the basics of the phase gradient autofocusing and the singular value decomposition are proposed. The developed theory is validated with the first experimental demonstration of HoloSAR over forested areas with an airborne SAR platform at P- and L-band. Keywords: Circular synthetic aperture radar (CSAR), compressive sensing (CS), holographic SAR tomography (HoloSAR), polarimetric SAR (PolSAR)
Bastian Calaminus "Die neue DLR-Richtlinie 'Software-Engineering'"
Mittwoch, 30. November 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In der Automobil-Industrie und vielen anderen Industrie-Zweigen ist Software heutzutage einer der wichtigsten Innovationstreiber. Genauso ist Software und deren Entwicklung ein wichtiger Bestandteil der täglichen Arbeit im DLR. Aus diesem Grund wurden die seit 2008 vorhandenen "DLR Software Standards" im letzten Jahr überarbeitet und in eine neuen Rahmenrichtlinie "Software-Engineering" überführt. Diese wurde dann im März 2016 freigegeben. Was die neue Richtlinie beinhaltet, wie man(n) die Neuerungen am besten umsetzen kann und auch noch etwas Allgemeines zu dem Thema ist der Inhalt meines Vortrags.
Koen Mouthaan "Digital Beamforming for Spaceborne Reflector SAR Systems via FIR Filter Networks in the Presence of Reflector Deformations"
Mittwoch, 30. November 2016
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Tandem-L is a proposed fully polarimetric bistatic spaceborne SAR mission with the aim to monitor dynamic processes on the Earth’s surface. The proposed radar satellite employs an array-fed reflector antenna with a digital feed-array for high sensitivity, high-resolution wide-swath SAR. With digital beamforming (DBF) multiple radar echoes can be tracked simultaneously on ground with high gain. In DBF, a priori information about the antenna patterns of the antenna is used. However, actual antenna patterns may vary due to deformations of the reflector resulting from, for example, in-orbit thermal effects. In this presentation, the impact of reflector deformations on antenna parameters in elevation and DBF performance in elevation is presented and discussed. Additionally, the impact of wideband chirps and wideband beamforming on DBF parameters is presented. The presentation concludes with recommendations for further research.
Tobias Rommel "Orthogonal Waveforms for Multiple-Input Multiple-Output Synthetic Aperture Radar"
Dienstag, 15. November 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In a MIMO-SAR system multiple waveforms are transmitted instantaneously and multiple receivers sample the echo signals. In a pre-processing step of the receiver, the transmitted waveforms must be separated and individually processed. To be able to split all possible channel combinations up in the post processing, different approaches can be considered. Basically, MIMO systems need for orthogonal waveforms, while orthogonal in that sense means that the transmitted waveforms are completely separable in the receiver. In MIMO-radar the information about the channel is of interest and the transmitted signals are known unlike in communication, where the users are usually interested in the information content of the transmitted signal. Therefore, it is necessary to adapt the techniques from communication to the fields of radar and SAR. While in most applications of MIMO-radar a few dedicated targets should be detected, in MIMO-SAR large homogenous surfaces are observed. This crucial difference leads to the fact, that no cross-correlation interferences between the signals can be accepted. Therefore a certain structure of the transmit waveforms and an additional spatial filtering via Digital Beam-Forming (DBF) on receive is required. From the current point of view, very promising waveform types for MIMO-SAR are OFDM chirp waveforms, sub-pulses, circular-shifted chirp waveforms and chirp diverse waveforms. All four types are treated during the presentation. High importance of this talk is given to the waveform comparison. Especially the Ambiguity Function (AF) is an important tool for waveform analysis in radar. To compare the waveforms in terms of interferences, this function is described in detail. For an objective analysis, a catalog consisting of several parameters, such as range resolution, Integrated Side-Lobe Ratio (ISLR), transmit energy, Doppler tolerance, practical implementation/spurious analysis and maximum number of transmit signals is compiled.
Manuele Pichierri "Multi-baseline Polarimetric SAR Interferometry for characterizing the biophysical properties of agricultural crops"
Dienstag, 25. Oktober 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Polarimetric Synthetic Aperture Radar Interferometry (Pol-InSAR) is an active remote sensing technique which combines interferometric measurements and polarimetric observations to yield quantitative information about the vertical structure of a vegetated surface. With respect to agricultural vegetation, this technique allows for the estimation of crop height and other metrics of the vegetation vertical structure (e.g. extinction coefficients and ground-to-volume ratios) that are expected to be sensitive to plant characteristics such as morphology, biomass and moisture. This study provides a first assessment of the potential of Pol-InSAR to characterize the structure and estimate the biophysical properties (e.g. vegetation height and biomass) of agricultural crops. To this end, a multi-baseline approach for crop parameter estimation is developed, i.e. a technique for inverting the oriented volume over ground (OVoG) scattering model. As opposed to previous studies, this approach accounts for the polarization-dependent extinction coefficient of canopies with a preferred orientation (e.g. owing to the alignment of leaves or stalks). The inversion scheme is applied to a data set of ground and airborne Pol-InSAR measurements in L-, C- and X-Band acquired during the DLR’s CROPEX14 campaign. The Pol-InSAR estimated OVoG parameters are then assessed through a comparison with in situ measurements of crop height, wet biomass and plant water content. The results of this investigation indicate the potential of Pol-InSAR to estimate the height of wheat and maize, provided the appropriate acquisition geometry (i.e. spatial baselines and radar look angle) and radar frequency (e.g. L- and C-Band for maize, C- and X-Band for wheat). For the first time, the study also provides quantitative evidence that the estimated OVoG parameters are sensitive to changes of crop structure, biomass and moisture. For instance, the estimated backscattering power from the canopy is associated with the in situ measured wet biomass during the growing season of maize and wheat. Moreover, the values of the estimated HH and VV extinction coefficients appear to be influenced by the alignment of the particles within the canopy (i.e. stalks for maize in L- and C-Band; ears for wheat in C- and X-Band).
Björn Möhring "Modular Simulation of a Compact Antenna Test Range"
Mittwoch, 12. Oktober 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
During my work on my master's thesis I developed a tool for the electromagnetic simulation of a dual reflector Compact Antenna Test Range (CTR) which is installed at the DLR in Oberpfaffenhofen. A CTR is an indoor antenna measurement facility which allows antenna measurements under far-field conditions. A model of this facility is simulated with both full-wave methods such as Method of Moments (MoM) and asymptotic methods such as Iterative Physical Optics (IPO) by means of the software tool Antenna Design Framework (ADF). Goal of this thesis is to obtain results and confirm the measurement performance of this chamber regarding magnitude and phase uniformity and the absence of cross-polarized field components in the test zone. Different feed antennas are used to draw out their impact on the measurement performance as well as the size of the test zone of this facility. Based on the findings of this thesis, additional research shall be performed to finds improvements in order to enhance the measurement capabilities of this chamber.
Manfred Thumm "Millimeter-Wave Gyro-Amplifier RADAR Systems"
Montag, 12. September 2016
11.15 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Future deep space telecommunication and Earth based RADAR for imaging of Near Earth Objects (NEOs) and the Solar system by Inverse Synthetic Aperture Radar (ISAR) as well as monitoring of space debris require higher transmitter power and higher microwave frequencies compared to running microwave systems. For RADAR applications it can be shown on the basis of the RADAR equation, assuming a similar propagation path (which is not true in reality), that a 35 m diameter antenna operating in Ka-band has a similar order of magnitude received signal strength as a 70 m antenna operating in X-band, provided that the transmitted power is similar and the target has a similar RADAR cross section for Ka- and X-band frequencies. Novel high-power millimeter-wave gyro-amplifiers operating in higher-order circular waveguide modes allow long distances and high range and angular resolution. The present seminar talk summarizes the worldwide state-of-the-art of gyro-klystron, gyro-traveling wave and gyro-twystron amplifiers in the Ka- and W-bands and reports on the Russian 34 GHz/1 MW (10 kW av.) phased-array “RUZA” RADAR system at Sary-Shagan in Kazakhstan, the 94 GHz/ 100 kW (10 kW av.) WARLOC RADAR system at the NRL in Washington, D.C., and the 8 GHz-bandwidth 55 kW (5.5 kW av.) W-band RADAR system HUSIR at the MIT Lincoln Laboratory in Westford, MA, USA.
John Jelonnek "Pulsed Power and High Power Microwave Technologies at IHM"
Montag, 12. September 2016
10.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The Institute for Pulsed Power and Microwave Technology (Institut für Hochleistungsimpuls- und Mikrowellentechnik (IHM)) is doing research in the areas of pulsed power and high power microwave technologies. Applications for pulsed power technologies are ranging from material processing to bioelectrics. High power microwave technologies are focusing on RF sources (gyrotrons) for electron cyclotron resonance heating of magnetically confined plasmas and on applications for material processing at microwave frequencies. The IHM is focusing on the long term research goals of the German Helmholtz Association (HGF). During the ongoing program oriented research period (POF3) of HGF (2015 – 2020), research projects are running within following HGF programs: “Energy Efficiency, Materials and Resources (EMR)”; “Nuclear Fusion (FUSION)”, “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” and “Renewable Energies (EE)”. The presentation will provide a comprehensive view over the research at IHM.
Jan Paul Kroll "Untersuchung und Modellierung von Hardwareeinflüssen auf MIMO-SAR Systeme"
Dienstag, 06. September 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Um die Restriktionen beim Synthetic Aperture Radar (SAR), hinsichtlich Abbildungsstreifenbreite und Azimutauflösung, zu umgehen, kann digitale Strahlenformung (DBF) eingesetzt werden. Die Signale werden im Digitalen entsprechend gewichtet so, dass z. B. die Hauptstrahlrichtung gesteuert werden kann. Eine Anwendung des DBF ist das Scan On Receive (SCORE). Hier wird mit einer Sendeantenne ein großer Abbildungsstreifen beleuchtet und die, durch DBF gesteuerte, Hauptstrahlrichtung des Empfangsarrays folgt dem Verlauf des Signals am Boden. So wird ein großer Abbildungsstreifen mit einem guten SNR realisiert. Dieser Vortrag soll einen Einblick in die Ergebnisse geben, die im Laufe einer Masterarbeit erarbeitet wurden. Es wurden der SCORE Pattern Loss (SPL) und der Pulse Extension Loss (PEL), als die Performance eines SCORE Systems beschreibende Parameter, untersucht und modelliert. Weiter wurden Möglichkeiten erarbeitet, wie diese Verluste reduziert werden können. Beim SPL wurde eine Approximation des digitalen Elevationsmodells benutzt um die Verluste zu verringern. Zur Reduktion des PEL wurden Variationen der Amplituden- und/oder Phasenbelegung, sowie eine frequenzselektive Formung von Subbeams angeschaut. Außerdem wurden noch die Auswirkungen von Restriktionen hinsichtlich der Gewichtungsfaktoren des DBF untersucht.
Steffen Wollstadt "OSCMS – Ocean Surface Current Mission Study: A Ku-band SAR Mission Concept for Ocean Surface Current Measurement using Dual Beam ATI"
Dienstag, 26. Juli 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The measurement of ocean currents at sub-mesoscale resolutions is still one of the major remaining challenges in order to understand the dynamics of ocean processes and ocean-atmosphere interactions. In order to progress in this observational gap the European Space Agency (ESA) has initiated a number of studies to develop a spaceborne mission concept, based on a dual-beam along-track SAR interferometer. One of the visible outcomes of these efforts has been the development of the Wavemill concept. In this line, in 2014 also a consortium consisting of OHB System, the DLR Microwaves and Radar Institute, MDA (Canada) and the NERSC Mohn-Sverdrup Center (Norway) has been awarded a contract for a system study to develop a mission and instrument concept for the two-dimensional measurement of the Total Ocean Surface Current Vector (TSCV), based on a single-platform dual-beam ATI-SAR system in Ku-band. The seminar reports on the major outcomes of this Ocean Surface Current Mission study (OSCMS) concerning the instrument concept, the performance based on the mission requirements as well as the necessary system parameter trade-offs. Furthermore a methodology of instrument requirement derivation is presented, assuring the required measurement accuracy. The dual-beam ATI concept requires two highly squinted antennas each looking simultaneously in fore and aft direction. The requirements on coverage and revisit-time are achieved with a single side-looking geometry and a ScanSAR imaging mode. Digital beamforming (SCORE) is used in order to fulfill the large sensitivity requirements and the applied hybrid polarization is intended to increase the information level about different ocean scattering mechanisms.
Julia Kubanek "Volcano monitoring with bistatic TanDEM-X SAR interferometry"
Mittwoch, 20. Juli 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Estimating the amount of erupted material during a volcanic crisis is one of the major challenges in volcano research. One way to do this is to assess topographic changes before and after an eruption while using area-wide 3D data. The bistatic TanDEM-X satellite mission enables for the first time to acquire 3D information of volcanoes repeatedly using the interferometric phase. A new data processing approach is presented in which TanDEM-X data are used to generate digital elevation models before, during, and after volcanic activity. For developing and validating the differential TanDEM-X digital elevation model approach, three test sites characterized by different patterns of volcanic activity that caused a topographic change are chosen. The first two test sites – Merapi in Indonesia and Volcán de Colima in Mexico – are dome-building volcanoes with varying activity. Whereas a major eruption which led to a topographic change of up to 200 m is analyzed at Merapi, a smaller explosive event with topographic changes of up to 20 m is investigated at Volcán de Colima. The third study focuses on mapping and measuring lava flow extent and volume during the fissure eruption of Tolbachik in Kamchatka that occurred in 2012-13. During the eruption which lasted for about nine month, 18 TanDEM-X data pairs are analyzed. The differencing of digital elevation models enables to estimate the amount of basaltic lava that was extruded over time and results in a final lava flow volume of 0.53 km³. The studies of all test sites indicate that TanDEM-X is suitable for revealing topographic changes at active volcanoes with a high accuracy. A comparison with aerophotogrammetric observations corroborate the TanDEM-X-based results. An extensive validation in areas where no topographic change is expected results in standard deviations for the elevation differences of ± 0.22 m for the Tolbachik test site and between ± 0.13 m and ± 0.59 m for Volcán de Colima, depending on the slope. The good accuracy corroborates that differencing digital elevation models from TanDEM-X results in reliable estimates of topographic and volumetric changes due to various kinds of volcanic activity, which allows – in the case of Tolbachik – to calculate lava extrusion rates.
Jalal Matar "Potentials and Limitations of MEO SAR "
Montag, 20. Juni 2016
13.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic Aperture Radar (SAR) systems play an important role in creating risk assessment models for areas that are most likely to face natural disasters; besides, crisis management benefits from the data provided by these systems, as a way to assess the distribution of the destruction and define rescue paths. Current Low Earth Orbit (LEO) SAR systems do provide us with these data, but the time required to get the data depends on the satellite’s passage time over the area. Increasing orbital altitude towards Medium Earth Orbit (MEO) heights provides advantages with respect to spatial coverage, global temporal revisit times and communications infrastructure. This allows us to have the same coverage as in LEO within few days. MEO SAR is capable of providing daily regional coverage and semi-global coverage within 3 days, using one satellite only. This presentation discusses various aspects of SAR missions in MEO. It covers the design of suitable orbits and their corresponding coverage, with emphasis on repeat ones. Furthermore, it analyses the changes in SAR performance as altitude increases, while addressing the potentials and limitations of high orbits. Throughout the presentation one interesting orbit, repeating its ground track every 3 days and providing near-global coverage, is studied.
André B. C. da Silva "A Priori Knowledge-Based STAP for Traffic Monitoring Applications: First Results"
Freitag, 03. Juni 2016
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Airborne monitoring of non-cooperative civilian road traffic is of great interest when the traffic information is required on a non-regular basis, as in the case of major events or disasters. Unlike military applications, where off-road targets also need to be detected, civilian applications require only the available road infrastructure on ground. Thus, since freely available road databases contain even small forest roads, e.g., the OpenStreetMap (OSM) database, the incorporation of a known road network in the processing chain is possible for detecting the targets and estimating their corresponding positions, velocities and moving directions. This seminar presents the first results of a novel a priori knowledge-based algorithm for traffic monitoring applications using the well-known post-Doppler space-time adaptive processing (PD STAP). The work is carried out in the frame of a PhD thesis. The algorithm includes a road network obtained from the OSM database fused with a digital elevation model (DEM) to recognize and to reject false detections, and moreover, to reposition the vehicles detected in the vicinity of roads. The proposed processor was verified using real pseudo 4-channel data (i.e., aperture switching data) acquired by the DLR’s airborne system F-SAR. The experimental results are discussed and compared with the results obtained by the conventional PD STAP without the benefits of a priori knowledge information.
Simon Zwieback "Analysing the influence of soil moisture and vegetation changes in differential interferometry"
Montag, 23. Mai 2016
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Displacement estimates produced by differential radar interferometry have become central to a wide range of scientific disciplines, including glaciology and geophysics. They are formed by combining two radar acquisitions taken at different instants of time, between which the soil moisture content can change. Soil moisture effects in differential interferometry have been associated with surface and subsurface scattering, and models that describe these effects have been proposed. In order to test the assumptions underlying these models, we conducted a radar experiment in which the subsurface contributions can be resolved. The observations are consistent with previous findings regarding the role of subsurface scattering – the soil moisture effects in differential interferometry are chiefly due to the changing propagation characteristics of electromagnetic waves through the soil - but they also indicate shortcomings of the way existing models are parameterized. As the depth-resolved measurements are closely related to soil moisture changes, we conclude that such depth-resolved observations have considerable potential for estimating soil moisture profiles. For standard, i.e. depth-averaged observations, the dual sensitivity of differential interferometry to displacements and to soil moisture changes raises two important questions. First, can soil moisture changes be estimated using differential interferometry in the absence of displacements? And second, can they be separated from deformations, e.g. to provide corrections for the estimation of displacements? Both the data and the theoretical analyses indicate that soil moisture estimation at the field scale is indeed feasible when displacements can be ruled out. However, they also suggest that, in practice, the second question cannot be answered in the affirmative without additional prior assumptions, chiefly due to the similar influence of displacements and soil moisture changes on the measurements. We also report on analyses of the impact of vegetation growth on zero-baseline differential interferometry at L-band. The changing propagation properties appear to exert a dominant influence on the measurements also for growing vegetation canopies; as opposed to soil moisture changes, the effect induced by biomass changes can be associated with a pronounced polarization dependence (> 90° HH-VV interferometric phase differences). The polarimetric diversity, which is not influenced by surface displacements, indicates potential ways of inferring biomass changes or of improving or screening displacement estimates provided by differential radar interferometry.
Antonio Martinez del Hoyo "Tomographic imaging of temporal decorrelated volume scatterers via multibaseline synthetic aperture radar"
Mittwoch, 18. Mai 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The upcoming space-borne SAR missions (BIOMASS, Tandem-L, SAOCOM, SAOCOM-CS) at longer wavelengths (L-/P-band) that will have tomographic capabilities on volume scatterers, such as forests and glaciers, will face the issue of temporal decorrelation. This is the loss of resolution and the biased information retrieval (over/under estimation of height, inner structures or the amount of biomass) caused by the changes (wind, moisture changes, seasonal changes, anthropogenic hazards) in the illuminated scenes during the multibaseline acquisition. The seminar will first review some of the existing mathematical models that try to explain the temporal decorrelation effect from the interferometric coherence, namely the Volume Temporal Decorrelation, the Polarimetric Scattering Media, the Exponential Model (plus Brownian or Markovian Motion) and the Height Dependent Variance model. Later on, a set of algorithms that have been used so far in this PhD thesis in the tomographic processing chain in order to improve the 3D reconstruction of forested areas will be presented: this are advanced direction of arrival estimators, scattering mechanisms separation techniques, advanced tomographic covariance estimation techniques and Diff-Tomo or 4D tomography. Results for TomoSAR and Diff-Tomo both with simulated and real F-SAR stripmap and circular data will be shown. Finally, future ideas to estimate and compensate for the temporal decorrelation effect will be presented.
Francisco J. Ocampo Torres "Plans to study ocean surface waves, wind fields and oil spill detection using SAR in the Gulf of Mexico"
Dienstag, 17. Mai 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
N/A
Felipe Almeida "Multichannel Staggered SAR Azimuth Sample Regularization"
Dienstag, 10. Mai 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Next-generation spaceborne SAR systems pose demanding and contradicting requirements on system design, owing to the increasing need to cover ultra-wide swaths with high azimuth resolution, as required for numerous applications. To this end, a large number of multichannel SAR system concepts have been proposed that employ digital beamforming on receive with planar arrays, and more recently also with reflector antennas. A further promising concept is staggered SAR which uses a single azimuth channel and multiple elevation beams together with variable pulse repetition intervals to map an arbitrary wide swath with medium resolution. To improve the azimuth resolution of such systems, this PhD Thesis examines the extension of the staggered SAR concept to a system configuration with multiple azimuth channels. For this, a new multichannel azimuth processing technique is introduced that combines staggered SAR gap interpolation with multi-channel SAR signal reconstruction. Simulations of a Tandem-L-like reflector SAR system with three azimuth channels show that this technique yields an excellent performance over a 350 km wide swath that is mapped with 3.0 m azimuth resolution. The seminar reports on the work done so far in the PhD Thesis, presenting an overview of the problem and explaining in detail the proposed solution. Simulated performance results as well as an error and sensitivity analysis for the method are addressed.
Scott Hensley "VERITAS: NASAs Discovery Mission to Venus and its X-Band Single Pass Radar Interferometer"
Freitag, 15. April 2016
13.30 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
NASA has selected 5 potential Discovery class missions for additional study prior to down selection of one or two missions in early 2017. The Venus Emissivity, Radio Science, InSAR Topography And Spectroscopy (VERITAS) Mission is a proposed mission to Venus that was selected as one of these missions. A deep understanding of solar system evolution is limited by a great unanswered question: How Earthlike is Venus? We know that these twin planets formed with similar bulk composition and size. Yet Venus followed a divergent evolutionary path, losing its surface water and becoming hotter than Mercury. How did this happen? The answer has profound implications for the potential for life in the universe and how terrestrial planets become habitable. The proposed VERITAS mission is designed to probe the geologic evolution of tesserae, look for buried features in plains of Venus, resolve the chronology of resurfacing events and look for signatures of tectonic deformation, e.g., subduction. VERITAS will look for evidence of geologic processes that are currently operating on Venus including volcanism, weathering and faulting. Finding evidence of past water through mineralogical investigations or present water through volcanic outgassing has major implication for the geologic evolution of Venus. It is designed to obtain high-resolution imagery and topography of the surface, using an X-band radar configured as a single pass radar interferometer (called VISAR) and a multispectral NIR emissivity mapping capability (called VEM). This talk will describe the science objectives of the mission, give an overview of the instruments and provide a more detailed overview of the VISAR radar.
Keith Morrison "Material Identification Using Extreme Wide-Band 10-50GHz SAR Imaging"
Freitag, 15. April 2016
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
This work reports on a laboratory-based study to assess the performance and unique intelligence capabilities of an ultra-wideband 10-50GHz SAR in the identification and discrimination between material types in a scene. Very high resolution range-profile measurements were obtained of samples used in building construction. The reflectivities showed clear frequency-dependent behaviours, and sliding sub-bands across the bandwidth revealed clear periodic resonances with frequency in the returns. These periodic features were interpreted as a resonance between the front and back face reflections of a sample. The feature's characteristics were in good agreement with the idea of a sample as a resonant microwave cavity. With knowledge of sample thickness, the spacing between nulls in frequency across the bandwidth allowed derivation of the permittivity. The resonance behaviour was preserved in SAR imaging of the samples, examined by sub-band analysis. The presentation will discuss both the opportunities and limitations the resonance phenomenon presents in terms of new information extraction capability from a SAR scene.
Michael Poland "TerraSAR-X and TanDEM-X: Critical tools for studying Hawaiian volcanoes"
Freitag, 11. März 2016
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic Aperture Radar has long been recognized as a critical tool for researching and monitoring active volcanoes. On the Island of Hawaiʻi, TerraSAR-X and TanDEM-X have proven to be particularly valuable owing to their high spatial and temporal resolution and ability to map topographic change. TerraSAR-X data covering Kīlauea Volcano have characterized a number of transient processes, including fault rupture and subsidence of the rim of the summit eruptive vent. Some of these phenomena would not have been detected without TerraSAR-X data. Likewise, TanDEM-X imagery has been revolutionary in Hawaiʻi, because the system provides the capability of capturing snapshots of topography over time. These data have allowed for mapping of lava flow activity at Kīlauea, and especially for determining the lava eruption rate—a parameter that could not be measured in any other way but that is especially important to assessing hazards due to eruptive activity. Lessons learned from Hawaiʻi are already being applied to volcanoes elsewhere in the United States and around the world. For example, TanDEM-X data are providing new information about eruptive activity at such volcanoes as Merapi (Indonesia), Colima (Mexico), Etna (Italy), Tolbachik (Kamchatka), and Soufrière Hills (Montserrat), while TerraSAR-X spotlight data are affording new insights into volcanic activity in Alaska, at Mount St. Helens, and at Yellowstone.
Paola Rizzoli "Snow Facies Investigation of the Greenland Ice Sheet using TanDEM-X Interferometric SAR Data"
Dienstag, 08. März 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The Greenland ice sheet is a vast ice-covered plateau extending for about 1,700,000 km2 over 80% of the whole Greenland surface. It represents the second largest ice body of the planet after the Antarctica ice sheet and its properties are significantly affected by temperature changes. The knowledge of the properties of the Greenland ice sheet can substantially contribute to better understand the arctic ecosystem and its responses to climatic changes. This work presents an approach for classifying the different snow facies of the Greenland ice sheet by exploiting X-band TanDEM-X interferometric synthetic aperture radar acquisitions. Large-scale mosaics of radar backscatter and volume decorrelation, derived from the interferometric coherence, represent the starting point for applying an unsupervised classification method based on the c-means fuzzy clustering algorithm. The detected snow facies can then be related to the well-known dry snow, upper and lower percolation, and wet snow/ablation zones. Results show a good agreement with external snow melt data and independent multi-temporal TanDEM-X data. Moreover, a statistical analysis of backscatter and volume decorrelation improves the knowledge and understanding of the derived snow facies. The proper location of the different facies finally allows to estimate the X-band penetration depth into the ice sheet. The presented approach represents a starting point for a long-term monitoring of ice sheets dynamics and could be applied to future radar missions as well.
Albin Gasiewski "Application of a CubeSat-Based Passive Microwave Constellation to Operational Meteorology"
Freitag, 26. Februar 2016
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In their most recent decadal assessment (Earth Application from Space, 2007) of Earth science space missions the U.S. National Research Council identified the Precipitation and All-weather Temperature and Humidity (PATH) mission as one of ten recommended medium cost missions. Based on the NRC’s outlined goals, PATH would have the unique capability of providing all-weather temperature and moisture soundings and cloud and raincell imagery at spatial scales comparable to AMSU-A/B or ATMS, but at sub-hourly temporal resolution. The essential need is to provide the atmospheric penetrability and spatial resolution of operational microwave sensors but with temporal resolution commensurate with the natural rate of evolution of convectively driven weather. This seminar will focus on the merits of a constellation of passive microwave sounding and imaging CubeSats for achieving PATH goals from the multiple viewpoints of calibration accuracy, data assimilation and global sampling, downlink capability and latency, and orbital lifetime and launch availability. Microwave spectral imagery at 50, 118, and 183 GHz with spatial resolution of ~10-30 km and temporal resolution of ~15-60 minutes from such a fleet could be expected to significantly enhance forecasting of mesoscale convective weather and hurricane rain band evolution, along with provide valuable temporal gap-filling data for synoptic weather forecasting. It is argued that from a joint technology, science, and operational standpoint that a cost-effective realization of the PATH goals, but with the additional features of global coverage and improved NWP sensitivity, can be achieved by a low-cost random-orbit constellation of CubeSats supporting the ATMS and 118 GHz bands. The CU PolarCube mission will be discussed as a basis for this fleet concept.
Dirk Fischer "System Architecture of a Polarimetric Multiparameter Phased-Array Radar"
Dienstag, 23. Februar 2016
15.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
This presentation describes the digital signal processing architecture and the radio frequency (RF) signal conditioning of the Digital Beamforming Weather Radar (DBWR) which is currently being developed at the Münster University of Applied Science. The basic architecture of the DBWR, its signal paths and signal processing as well as the polarimetric multiparameter intrapulse modulation techniques and the possibilities to evaluate the received signals are presented. With some scaling this system is capable to gain much higher resolution by expanding the bandwidth to several 100 MHz, therefore other applications than measuring weather processes are a future option. With the specification of modulation parameters, special routines generate the complete transmitting pulse in a simple Lookup Table (LUT) which can be transmitted in the digital signal processing unit, implemented in a System on Chip based (SoC) Field Programmable Gate Array (FPGA). The signal processor itself is responsible for the subsequent processing, the implementation of the phased-array functionalities and the output of the transmitting signal at an Intermediate Frequency (IF) of currently 44.6875 MHz. The IF of the 3rd generation of the DBWR will be in the range of 1 GHz. In the specification of the transmitting pulse the intrapulse modulation of frequency, amplitude and phase as well as the modulation of the polarization, based on a predefined polarization ellipse over the complete duration of the pulse width (PW), is feasible. By mixing the generated signal with a Direct Digital Synthesis (DDS) signal in an FPGA which is variable in phase and amplitude, it is possible to implement and calibrate the phased-array functionality without any influences on the modulations. The following RF-Front-End is responsible for the up- and down-conversion, filtering and amplification for the X-Band-Radar functionalities. The raw data of the received signal can be send back to software and with the known modulation and the phase-/amplitude-offsets of the mixed signal, it can be evaluated in different ways to determine the most effective algorithm for the single receive signal parameters.
Michelangelo Villano "Staggered Synthetic Aperture Radar"
Mittwoch, 17. Februar 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic aperture radar (SAR) remote sensing allows high-resolution imaging independently of weather conditions and sunlight illumination and is therefore 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 imaged at the expense of a degraded azimuth resolution. This limitation can be overcome by using systems with multiple receive subapertures 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: Multiple subswaths can be, in fact, simultaneously imaged using digital beamforming in elevation, but “blind ranges” are present between adjacent swaths, as the radar cannot receive while it is transmitting. Staggered SAR overcomes the problem of blind ranges by continuously varying the pulse repetition interval (PRI). A proper selection of the PRIs, together with an average oversampling in azimuth, allows an accurate interpolation of the non-uniformly sampled raw data on a uniform grid, so that resampled data can be then focused with a conventional SAR processor. This concept therefore allows high-resolution imaging of a wide continuous swath without the need for a long antenna with multiple subapertures. As an additional benefit, the energy of range and azimuth ambiguities is spread over large areas: Ambiguities therefore appear in the image as a noise-like disturbance rather than localized artifacts. In this thesis, the impact on performance of the selected sequence of PRIs, the adopted interpolation method, and the processing strategy are addressed. Design examples for single-, dual-, and fully-polarimetric staggered SAR systems are presented, based on both planar and reflector antennas, in L-band and C-band. The impact of staggered SAR operation on image quality is furthermore assessed with experiments using real data. As a first step, highly oversampled F-SAR airborne data have been used to generate equivalent staggered SAR data sets and evaluate the performance for different oversampling rates. Moreover, the German satellite TerraSAR-X has been commanded to acquire data over the Lake Constance in staggered SAR mode. Measurements on data show very good agreement with predictions from simulations. Furthermore, a data volume reduction strategy, based on on-board Doppler filtering and decimation, has been developed to cope with the increased azimuth oversampling of staggered SAR. Finally, a patented extension of the staggered SAR concept is provided, where the phase centers are continuously varied as well, so that it is possible to transmit pulses according to a sequence of different PRIs and acquire uniformly sampled data without the need of any interpolation. The staggered SAR concept is currently being considered as the baseline acquisition mode for Tandem-L, a proposal for a polarimetric and interferometric spaceborne SAR mission to monitor dynamic processes on the Earth’s surface with unprecedented accuracy and resolution.
Björn Döring "Traceable Radiometric Calibration of Synthetic Aperture Radars"
Dienstag, 16. Februar 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Radarsysteme mit synthetischer Apertur, sogenannte SAR-Systeme, sind veritable Messgeräte. Wurden SAR-Abbildungen in früheren Jahren zunächst ausschließlich zur Zieldetektion und Kartographie genutzt, so werden radiometrische Messdaten heute für vielfältige Anwendungen auch quantitativ genutzt. Mit Hilfe von physikalischen Modellen reichen die Anwendungen dabei von der Bestimmung der Wald-Biomasse hin zur Vermessung der Bodenfeuchte oder der großflächigen Bestimmung der Windgeschwindigkeit auf dem offenen Meer. Diese Parameterinversionsanwendungen setzen kalibrierte SAR-Systeme voraus, damit einmal abgeleitete Modellparameter ihre Gültigkeit behalten. Ein wichtiger Aspekt der Kalibrierung ist dabei die metrologische Rückführbarkeit, also die Eigenschaft eines Messergebnisses, durch eine dokumentierte, geschlossene Kette von Kalibrierungen unter Berücksichtigung der Messunsicherheiten auf eine Referenz bezogen werden zu können. Im Zentrum der Arbeit steht die Aussage, dass Messergebnisse für radiometrische SAR-Messungen derzeit nicht rückführbar sind. Dadurch ist eine Vergleichbarkeit verschiedener Datenprodukte nicht gewährleistet und es besteht die Gefahr, in wissenschaftlichen und kommerziellen Anwendungen Falschaussagen zu treffen. In diesem Zusammenhang werden in der Arbeit fünf Beiträge geliefert, um die Rückführbarkeit für radiometrische Messergebnisse zu erreichen: • Zunächst wird die neue Messgröße „äquivalenter Radarrückstreuquerschnitt“ (engl. equivalent radar cross section – ERCS) eingeführt. Dies ist notwendig, da die bisherige Messgröße „Radarrückstreuquerschnitt“ (engl. radar cross section – RCS) weder dem Einfluss der komplexen Phase im reflektierten Signal noch der gewichteten Mittelwertbildung in der SAR-Prozessierung über Frequenz und Winkel gerecht wird. • Weiterhin wird ein numerisches Verfahren entwickelt, mit dem die bekannte Messgröße RCS mit der neu eingeführten Messgröße ERCS verknüpft werden kann, eine Voraussetzung für die metrologische Rückführbarkeit. • Es wird ein analytisches Modell abgeleitet, mit dem der Einfluss der Übertragungsfunktionen von einem SAR-System (insbesondere der Gewichtungsfunktionen zur verbesserten Nebenkeulenunterdrückung) und einem abgebildetem Punktziel auf radiometrische Messungen quantitativ bestimmt werden kann. Weiterhin wird das Problem der in der Praxis uneinheitlich eingesetzten Gewichtungsfunktionen in der SAR-Prozessierung thematisiert und Lösungsvorschläge aufgezeigt. • Zur Kalibrierung des Radarrückstreuquerschnitts von aktiven radiometrischen Kalibriernormalen, sogenannten Transpondern, wird die neue Dreitranspondermethode entwickelt und deren praktische Umsetzbarkeit durch eine Messreihe demonstriert. Die Methode erlaubt, die Standardunsicherheit von bisher typisch 0,21 dB auf 0,08 dB erheblich zu reduzieren, wobei eine direkte Rückführbarkeit des Messergebnisses auf ein Primärnormal des Meters möglich ist. • Außerdem wird erstmals der Ansatz der hierarchischen Modellierung, einem Teilgebiet der Bayesschen Statistik, für die Bestimmung der radiometrischen Messunsicherheiten im Gebiet der SAR-Kalibrierung eingeführt. Die Methode erlaubt, bei gleicher Datenerhebung bisher verworfene Informationen auszunutzen die so zu genaueren Parameterschätzungen und damit letztendlich zu genaueren radiometrischen SAR-Messungen führen. Die mit den Beiträgen erreichte metrologische Rückführbarkeit erlaubt die uneingeschränkte Vergleichbarkeit radiometrischer Messergebnisse. Diese ist dringend erforderlich, da die Anzahl von existierenden SAR-Satelliten ständig steigt. Erst mit der direkten Vergleichbarkeit wird ein fundierter Datenaustausch zwischen verschiedenen Systemen möglich, der wiederrum weitere wissenschaftliche und kommerzielle Synergieeffekte freisetzen kann. Die vorliegende Arbeit liefert dafür einen wichtigen Beitrag.
Martin Maier "Quality management for a scientific environment – The HR process for science, research and development"
Donnerstag, 04. Februar 2016
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Quality management in a scientific environment is a challenge for both sides (scientists and quality manager). On one hand, scientists want a flexible and open environment to do their research, on the other hand quality manager loves straight and tight processes and structures. The HR process will combine both sides in common process. The seminar will provide an overview of the proposed HR process and will be the starting point for the discussion of future improvement of our research environment. During the seminar we will also discuss the existing concerns and doubts.
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