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Vorträge im Institutsseminar 2010
Iole Pisciottano "First Analysis on Snow Cover Change Using Polarimetric TerraSAR-X Data"
Dienstag, 21. Dezember 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Snow represents a basic reservoir of water within the global ecosystem. Over the last three decades global warming caused a substantial decline of this resource. Therefore the monitoring of snow cover dynamics plays an important role for the assessment of climate change. This investigation will provide first insights into the sensitivity of fully polarimetric X-band data of TerraSAR-X with respect to snow parameters and temporal changes of the snow layer. The TerraSAR-X data are used for a first comparison with an electromagnetic snow scattering model of the CoReH20-mission incorporating field and meteorological data from collaboration partners in Sodankylae, Finland. In addition a model-based polarimetric decomposition was developed and applied on the space-borne PolSAR data for a first analysis of the surface and volume scattering mechanism within the snow pack.
Marcelo Schiller Lorande "Estimation of Moving Target Velocity Parameters with Air- and Spaceborne Multi-Channel SAR Systems"
Dienstag, 7. Dezember 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
For traffic monitoring applications using multi-channel synthetic aperture radar (SAR) systems operating on air- or spaceborne platforms the vehicles moving on ground have to be detected and their motion parameters have to be estimated. Up to now, with DLR’s airborne F-SAR system as well as with the spaceborne TerraSAR-X Dual receive antenna mode only two channels of an along-track array have been combined coherently for purposes of ground moving target indication (GMTI) using techniques such as displaced phase center antenna (DPCA) and along-track interferometry (ATI).
This work steps from target motion parameter estimation using two-channel techniques (ATI) to multi-channel STAP techniques. The drawback of two-channel target motion parameter estimation techniques such as ATI is that they cannot handle situations where moving target signals interfere with high clutter environments. By use of multi-channel STAP techniques and along-track arrays with more than two channels enough degrees of freedom are available such that even high clutter can be suppressed and at the same time target motion parameters can be estimated.
In the frame of this work various STAP parameter estimation algorithms are implemented and tested. The performance of the estimators is tested by use of Monte-Carlo simulations and compared to the Cramer-Rao Lower Bound (CRLB). In a next step the estimators are tested with experimental F-SAR four-channel X-band data and the performance achieved with the real data is compared to the performance predicted by the CRLB and achieved in the Monte Carlo simulations in order to evaluate the quality of the performance prediction.
With airborne radar systems and GMTI applications usually high PRF values are used such that the stationary world signals are highly oversampled. This is not possible with spaceborne radar systems due to swath width restrictions induced by the range ambiguities. For spaceborne multi-channel SAR systems range and azimuth ambiguities usually have to be considered for GMTI applications and the choice of the antenna length, the number of channels and the PRF are critical parameters in the multi-channel SAR satellite system design. Since the STAP parameter estimation techniques provide a general processing rule for coherently combining the signals from along-track arrays with arbitrary number of channels, arbitrary arrangement of the channels (as long as the system can be considered quasi-monostatic) and PRF they can also very well be used for the multi-channel SAR satellite system design. The impact of the antenna length, the number of channels and the PRF on the predicted moving target motion parameter estimation accuracy is shown for various near-future multi-channel SAR satellite system concepts.
Gabriel Castellanos Alfonzo "Performance Investigation of a Highly Digitized Radar at X-Band"
Dienstag, 30. November 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The performance of a highly digitized radar system called "GigaRad" was investigated. The GigaRad system is a new concept for a highly- digitized radar instrument to reduce the amount of analogue components to a minimum. A prototype was built in a previous work and has two key functioning elements: a high speed analogue to digital converter and an arbitrary waveform generator. The high sampling frequency of both elements enables the transmission and reception of wideband signals. In this work, the experimental prototype of the GigaRad system was expanded from one to two transmitter channels, each one fed by an orthogonal radar signal. Since the behaviour of the transmitted signals affects the resolution in the range direction of the system, a careful waveform design and performance study was done. The autocorrelation and cross-correlation properties of different radar waveforms known from the literature were studied and verified with ISAS measurements
Laís Sant'Anna Araujo “Coregistration Issues in TOPS and ScanSAR Interferometry and First Investigations of Sea Ice Dynamics Using TerraSAR-X and TanDEM-X Data”
Dienstag, 16. November 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Coregistration is a critical processing step in interferometric ScanSAR and TOPS data processing due to the azimuth variant properties of the impulse response function, which is imposed by the antenna steering during data acquisition. The work to be presented first investigates the coregistration with TerraSAR-X data of a stable area without movement and presents next the difficulties for TOPS and ScanSAR interferometry for natural areas characterized by surface displacements as occurs on glaciers in between the 11 days of successive TerraSAR-X orbits.
In this first part is explained the Spectral Diversity method for estimating the misregistration values between an interferometric pair. This estimate is usually applied to coregister the pair, giving a higher quality interferogram, but can also be used to investigate slow displacements in the Earth surface.
The second part of the work is dedicated to ScanSAR interferometry performed in along track interferometric mode. With the new data from TerraSAR-X and TanDEM-X, it is possible to obtain detailed information about the sea ice blocks motion.
In addition to the misregistration estimate, a local frequency investigation is made to measure the fringe rate in azimuth direction noticed in the sea ice blocks from a Greenland area and it is explained how it is related to a horizontal rotation of the blocks.
Johanna Dall'Amico of LMU, Munich "Soil Moisture from L-Band Radiometry: Calibration and Validation of ESA's Soil Moisture and Ocean Salinity (SMOS) Mission in Southern Germany"
Dienstag, 9. November 2010
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The Soil Moisture and Ocean Salinity (SMOS) mission, launched by the European Space Agency in November 2009, carries the first ever spaceborne interferometric L-band radiometer with the objective of providing a global dataset of soil moisture and ocean salinity. In order to validate the Level 2 soil moisture products, the maintenance of long term soil moisture monitoring sites is required, matching the spatial resolution of the sensor in the order of 40 km. The Upper Danube catchment, a temperate agricultural area situated mostly in Southern Germany, has an area of 77000 km² and is one of two major SMOS cal/val test sites in Europe. The SMOS cal/val approach is based on local in-situ soil moisture measurements, distributed high resolution land surface modeling, use of ancillary remote sensing data as well as ground based radiometer measurements and airborne campaigns. The aim of the presentation is to inform about the on-going activities, gained data sets and first results.
Alicja Kosc "Simulation, Aufbau und Test einer Antennenzeile als Untergruppe einer P-Band Antenne für Flugzeug -SAR Anwendung"
Donnerstag, 21. Oktober 2010
11.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Der Diplomvortrag beschreibt die Entwicklung von Komponenten einer P-Band Gruppenantenne für Flugzeug SAR. Hinsichtlich der mechanischen Beanspruchung ist ein geeignetes Design, elektrisch wie mechanisch, zu finden um den Anforderungen im operationellen Betrieb der Antenne gerecht zu werden. Hohe Pulsleistung, Strahlschwenk in drei Positionen und Festigkeit sind wichtige Designparameter für die P-Band Antenne. Die Entwicklung der Untergruppe ist auf diesen Betrieb der Gruppenantenne auszulegen. Die Azimutcharakteristik der Untergruppe ist auf die endgültige Antenne abzustimmen. In beiden Polarisationsrichtungen, linear horizontal und vertikal, ist das Netzwerk auf optimale Amplituden- und Phasenansteuerung auszulegen.
Andrés Bertetich "Investigation of Multi-Channel SAR Calibration Methods for Real-Time Traffic Monitoring"
Dienstag, 14. September 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
For traffic monitoring applications using multi-channel synthetic aperture radar (SAR) systems operating on high altitude it is essential, that the vehicles moving on ground can be detected and their parameters can be estimated in near real-time. In general software based adaptive calibration of each receiving channel has to be performed prior to ground moving target indication (GMTI) and parameter estimation. The calibration method used at present prevents real-time traffic monitoring, since the required computational load is very high.
In the frame of the master thesis existing and new channel calibration methods were investigated and implemented. The performances as well as the influence of these methods on the moving target signals were compared using experimental multi-channel SAR data acquired with DLR’s airborne F-SAR system. Results were analyzed in order to have some hints on where the actual calibration method used in the GMTI processor can be improved.
Giuseppe Parrella "Analysis of LiDAR data for multi-parametric SAR derived forest height validation"
Freitag, 13. August 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Forest height is one of the main parameters for the management and monitoring of forested areas. The objective of this work is to compare forest height estimates from different remote sensing systems: Airborne Lidar (TopScan GmbH with a Riegl Sensor), Spaceborne Lidar (ICESat/GLAS) and Radar PolInSAR (E-SAR). Investigations were done over the test site “Thüringer Wald”, a temperate coniferous forest placed in a hilly topography with strong slopes.
ICESat/GLAS is a full waveform LiDAR system with a footprint size of 65m. The GLAS dataset for the test site encloses three acquisition tracks for the period from 2004 to 2007. Airborne LiDAR data were acquired in 2003 and 2004, providing a 5m resolution DTM (ground echoes) and DSM (vegetation echoes). The L-band PolInSAR dataset were acquired by DLR’s E-SAR system in 2009, in an ascending and a descending mode (two different look directions).
Because of the strong topography in the test site, slope correction plays a crucial role in the analysis of the different data sets.
Height estimates of the different data, with particular focus on the ICESat/GLAS waveform analysis, will be compared and discussed.
Jayanti Sharma "Estimation of Glacier Ice Extinction using Long-wavelength Polarimetric Interferometric Synthetic Aperture Radar"
Dienstag, 10. August 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In recent years there has been increased interest in using synthetic aperture radar (SAR) to study and monitor glaciers and ice sheets for glaciological and climate change research. Further extensions to SAR including interferometric SAR (InSAR), polarimetric SAR (PolSAR), and a combination of the two (Pol-InSAR) offer additional potential in quantifying glaciological parameters such as the ice extinction coefficient. Extinctions are useful in characterising regions of volume scatter which are related to the presence of melt structures, and could thus be used as a proxy indicator for changes in glacier mass balance and regional climate.
In this presentation a new scattering model relating long-wavelength Pol-InSAR observables to the ice extinction coefficient is introduced. Pol-InSAR coherences are modelled as a combination of a surface contribution (from the snow-ice interface and wind-induced sastrugi features) and a volume response. Surface-to-volume scattering ratios derived from a novel polarimetric decomposition are used in conjunction with Pol-InSAR coherence magnitudes to invert the extinction of the ice layer. The inversion is performed on experimental airborne Pol-InSAR data at L-band (1.3 GHz) and P-band (0.35 GHz) acquired by DLR's E-SAR system over the Austfonna ice cap in Svalbard, Norway as part of the SVALEX 2005 and ICESAR 2007 campaigns. Extinction dependencies on frequency and glacier zone are investigated, and validation is performed comparing ground penetrating radar data and airborne sounder data to SAR backscatter and extinction values.
Jaime Hueso-Gonzalez "Investigation of the multipactor effect in space-borne waveguide devices"
Dienstag, 11. Mai 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The multipactor effect is a known phenomenon consisting of an electron avalanche/discharge in microwave devices operating under high power and vacuum conditions. Multipactor discharges disrupt the electromagnetic response of RF devices and increase the temperature in the metallic surfaces of the waveguides, even leading to metal outgassing, ionization of the particles and physical damage/melting of the device (Corona). This problem especially affects space hardware (like travelling wavetubes TWTs in SAR instruments), since, in orbit, most of the conditions responsible for this discharge are fulfilled. Therefore, sensitive satellite flight hardware has to undergo thorough and expensive multipactor testing for its space qualification.
In order to reduce these costs and increase the multipactor-free power range of hollow waveguides, an innovative geometry is proposed in this work, consisting of a wedgeshaped waveguide with inclined top and bottom walls. An analysis tool has been developed that is able to efficiently calculate the electromagnetic fields in this kind of waveguides by means of the BIRME method, and derive the voltage between top and bottom plates. Additionally, a prediction tool tracks the movement of an electron within the wedge-shaped waveguide (Velocity Verlet algorithm) under the influence of the fundamental mode EM-fields. The combination of these tools allows for statistically predicting the presence of multipactor discharges in the device under the selected transmitted power, conductor material and geometry conditions. The results include a study of the optimal inclination angle of the wedge-shaped geometry, and a set of design rules for applying this innovative structure to more complex devices, like waveguide pass-band filters. Finally, experimental results are shown, which have been carried out in the Payload Systems Laboratory in ESTEC (ESA), the Netherlands.
Philipp Looser "RF Design of a Transponder for Calibrating Spaceborne SAR Systems"
Donnerstag, 06. Mai 2010
10:30 Uhr Großer Besprechungsraum HR, Gebäude 102
Abstract:
Accurate calibration of spaceborne SAR systems is based on precise reference targets with well known characteristics like the radar cross section (RCS) or the stability. Only then, the image information can be transformed in geophysical units like the backscattering characteristics of the Earth surface or digital elevation models. To satisfy the growing demand for such precise SAR data products, the calibration group is developing a new transponder for the calibration of future SAR-systems. To meet the stringent requirements concerning accuracy and stability, the transponder includes an internal calibration loop to compensate the temperature effects and the components' ageing. The topics of this presentation include the design of the analog front-end, the development of an adequate internal calibration strategy, and stability considerations. Improvements of the new design are shown by a comparison to transponders already deployed for different SAR missions. Based on this approach, the different error sources have been identified and where possible simulated or measured.
Claudia Hilbert, Nicolas Ackermann and Tanvir Ahmed Chowdhury "3 PhD presentations from the Department for Earth Observation, University Jena, on radar applications for forest mapping in the "Thüringer Wald"
Dienstag, 4. Mai 2010
14.00 h Großer Besprechungsraum HR, Gebäude 102
Claudia Hilbert: "Mapping 3D forest structure using satellite multifrequency radar and lidar data in the Thuringian Forest, Germany"
Abstract:
The current status of a study combining lidar and radar data for forest height and biomass estimation are presented. The objective of the study is to develop a methodology for mapping the three-dimensional forest structure using satellite, multifrequent radar and lidar data.
TerraSAR-X, ALOS PALSAR and ICESat/GLAS data for a test site in the Thuringian Forest are investigated. TerraSAR-X data have a high spatial resolution and are aimed to analyse the horizontal forest structure. ALOS PALSAR data are used to identify the vertical structure and ICESat/GLAS waveforms provide direct estimations of tree height for the footprint sites. A forest inventory GIS database will be used for a stepwise calibration and validation of the remote sensing based method. Additionally, digital orthophotos and an airborne lidar based Digital Height Model (DHM) are use d to assess the forest conditions in the test site.
The presentation will introduce the objectives and the status of the ongoing work. The calculation of the airborne lidar based DHM will be explained as well as the calculation of the GLAS waveform parameters. Some first results showing a comparison between the GLAS metrics and the DHM will be shown. Also, a first analysis of ALOS PALSAR and the DHM will be presented.
Nicolas Ackermann: "Potential of fusion of SAR and Optical satellite imagery for biomass estimation in temperate forest areas"
Abstract:
The application of remote sensing techniques in the retrieval of forest stand proprieties, especially biomass and stem volume, has been intensively investigated during the last few years. New methods using SAR and Optical systems have been pointed out. However, these instruments present intrinsic limitations which prevent operational biomass retrieval while using them separately. In order to overcome SAR and Optical system restrictions with respect to biomass mapping, the present study will assess the potential of fusion of these two different sources of information. The Thuringian Forest located in the center of Germany has been chosen for the investigations. An extensive set of L-Band data (ALOS PALSAR) and X-Band data (TerraSAR-X, Cosmo-SkyMed) has been acquired in various sensor configurations (acquisition modes, polarizations, incident angles). High resolution optical data (RapidEye and Kompsat2) has been also acquired and a forest inventory with a great deal of forest stands has been delivered. The presentation will first concentrate on the pre-processing of the data. A data analysis will then be presented and preliminary results will be discussed with a view to the fusion of SAR and Optical information. The fusion of SAR and Optical systems has the potential to give new possibilities in terms of temporal and spatial transferability. In this context, it will be expected to increase the biomass map accuracy, its spatial extension and its updated frequency.
Tanvir Ahmed Chowdhury: "Assessment of the potentiality of L-band quadpol radar for the retrieval of forest structural parameters by means of polarimetric information in Central Siberia and Thueringian Forest"
Abstract:
Recent studies showed that there is a correlation between backscatter coefficient of synthetic aperture radar (SAR) and the retrieval of growing stock volume, GSV. However, it was also recognized that the saturation level of the radar backscatter is quickly achieved, despite further increases of GSV. To avoid this effect, polarimetric techniques may be one of the solutions to increase the saturation level of GSV. This includes the derivation and investigation of various polarimetric indices involving different decomposition parameters. L-band polarimetric synthetic aperture radar data acquired by ALOS-PALSAR over thousands of forest stands in the Thueringian Forest have been evaluated for the derivation of forest parameters with focus on GSV. A large set of inventory ground data such as tree age, tree height, tree diameter, tree volume, relative stocking and dominant species of composition were measured of these large forest stands.
The presentation will be initiated by establishing a relationship between GSV and polarimetric phase difference, where sensitivity for forest parameters and saturation level increment are expected. Afterwards polarimetric parameters derived from decomposition techniques will be investigated. Further forest parameters to be implemented in this study are tree height, tree diameter, tree age, relative stocking, and tree species.
Francesco Scotto di Clemente "Precise motion compensation for very high-resolution repeat-pass airborne SAR interferometry in the presence of high topography variation"
Montag, 03. Mai 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Motion compensation is one of the most critical processing steps for airborne SAR focussing. The high demands concerning the accuracy of motion compensation originate from applications like multibaseline polarimetric SAR interferometry, SAR tomography as well as differential SAR interferometry. During the recent years the E-SAR system of DLR-HR has been operated mainly in these modes. However, the future data supply for the development of novel SAR techniques and applications will be provided by the new F-SAR system offering improved spatial resolution, simultaneous acquisition in up to 3 frequency bands and in future also single-pass interferometry in X- and S-band.
In this context, the Precise Topography and Aperture (PTA) dependent motion compensation algortihm is re-investigated in this thesis and a improved 2D PTA approach is proposed to overcome the limitations of the PTA approach established for the E-SAR system. The method is validated on simulated and real F-SAR data in S- and X-band and the tradeoff between efficiency and precision of the processing is discussed.
Keith Morrisson "Evidence for a DInSAR Phase Signature of Soil Moisture"
Montag, 26. April 2010
14:00 Uhr s.t. Besprechungsraum im Vorstandsgebäude, 2. Etage
Abstract:
Differential interferometric SAR (DInSAR) is used for the detection and accurate monitoring of surface movement in a scene, and has found applications in fields such as mining subsidence and earthquake deformation. In these studies, the phase is understood to directly relate to the radial component of the physical vertical movement of the surface horizon. However, recent reports have suggested that in some cases these phase variations are related to soil moisture variations, either indirectly through swelling/shrinkage or directly through a change in bulk dielectric properties. To investigate these claims further, an extended laboratory-based study was undertaken to investigate the DInSAR phase behaviour of a sandy soil to varying moisture content. The presentation discusses the results of the work, which has implications for the classic interpretation of the interferometric signal, and instead, use of the DInSAR phase as a proxy for soil moisture. Timelapsed movies are used to provide a dynamic appreciation of the temporal and spatial development of the interferometric phase in response to varying moisture content
Xiaoxiang Zhu und Richard Bamler"Differential SAR Tomography - The Compressive Sensing Approach"
Dienstag, 20. April 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Differential SAR tomography (D-TomoSAR) extends the synthetic aperture principle into the elevation and time directions for 4-D (space-time) imaging. It is essentially a 2-D spectral estimation problem. With modern meter-resolution space-borne SAR systems like TerraSAR-X systematic tomographic imaging of urban infrastructure and its deformations becomes feasible. The high resolution fits well to the inherent scale of buildings (floor height, distance of windows, etc.).
Compressive sensing (CS) is a new and favorable sparse reconstruction technique. It aims at minimizing the number of measurements to be taken from signals while still retaining the information necessary to approximate them well. This presentation introduces the basic principle and some properties of this technique applied for D-TomoSAR. Compressive sensing is shown to provide a good compromise between classical parametric and non-parametric spectral analysis methods. Compared to parametric spectral analysis, CS is more robust to phase noise, has lower computational effort, and does not require model selection to provide the prior knowledge about the number of scatterers in a resolution cell. Compared to non-parametric spectral estimation CS overcomes the limitation of elevation resolution caused by the extent of elevation aperture, i.e. CS has super-resolution properties. Numerical simulations for realistic acquisition and noise scenarios will be presented to evaluate the potential and limits of the technique. The first CS D-TomoSAR results with TerraSAR-X spotlight data over urban areas will be presented.
Esra Erten "Information Theory of Multi-Temporal SAR Systems with the Application to Change Detection"
Dienstag, 13. April 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
This work proposes a new method for change detection measurement independent from system configuration in a set of multi-temporal-multidimensional SAR images. The method is based on the special case of the Kullback-Leibler (KL-divergence) test, known as Mutual Information. In order to develop an algorithm independent from the system configuration, firstly the joint distribution of PolInSAR data set, based on the second order statistics has been derived. Such a derivation accounts for the whole multi-temporal system configurations as interferometric and partial-PolInSAR data sets. Then the KL-divergence test is used to measure the difference between the joint density of multi-temporal PolSAR data set and their marginal density known as complex Wishart distribution. A comparison between the proposed and the other well-known change detection (e.g. cross correlation and the maximum likelihood ratio test) techniques is shown, describing the advantages due to the fact that the proposed change detector involve almost every facet of applied change detection.
Marc Jäger and Olaf Hellwich "Leveraging Spatial Context in the Automatic Clustering of Polarimetric SAR Data"
Dienstag, 6. April 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
This talk outlines a framework for the fully automatic clustering (also known as 'unsupervised classification') of polarimetric SAR data. The algorithms discussed partition a given image into a set of homogeneous regions by assigning a label to each observation on the basis of local radiometric information. These techniques are potentially useful as part of fully automated processing chains: a good example is image registration or data fusion based on segment shape.
The topics covered in the talk include a brief review of expectation maximization, a new mechanism for model order selection (i.e. determining a suitable number of clusters) using Bayes factor analysis and the use of Markov random fields for spatial regularization. The results presented cover real and simulated polarimetric SAR data and the generalization to other types of image data is discussed.
Boris Jutzi "Modelling and Analysis of full-waveform laser data"
Freitag, 26. März 2010
9:30 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Pulsed laser scanning systems determine the range to an illuminated object by a time-of-flight measurement. The time-of-flight is typically derived by the elapsed time between the emitted and backscattered laser pulses. Critical measurement situations can occur if the temporal waveform of the backscattered pulse is strongly deformed or more than one pulse is backscattered. Such kind of backscattered pulses can be expected for natural, as well as for man-made objects, like the canopy and the branches of trees, and different elevated building edges or sloped roof areas. Critical measurement situations can be investigated by the analysis of the temporal waveform to improve the capabilities of terrestrial and airborne laser scanning systems. Due to the varying received waveforms, a model is invented, which considers the transmitted waveform of the emitted laser pulse, the spatial energy distribution of the laser beam, the reflectance properties of the surface as well as the atmospheric transmission of the laser beam on the way from the sensor to the surface and the receiver characteristic. The modeling of complex surfaces requires a large effort for the calculations of the simulation.
To carry out the experiments the transmitted and received waveform is recorded separately with 20 GSamples/s. Therefore the waveform of each individual pulse can be recorded in detail. For analysis a deconvolution is utilized to remove the characteristic of the transmitted waveform from the received waveform to obtain a surface response.
Ernesto Imbembo "Effect of Temporal Decorrelation for Forest Height Inversion using Repeat Pass TerraSAR-X Data"
Dienstag, 23. Februar 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
The estimation of forest parameters (in particular forest height) in X band using the Random- Volume-over-ground model has been demonstrated successfully several times using long wavelenght airborne Pol-InSAR data. TerraSAR-X provides for the first time interferometric X-band data from space in a repeat pass mode. As X-band is highly affected by temporal decorrelation a repeat pass time of 11 days makes it difficult to get suitable data sets for this purpose. Additionally the available spatial baselines are formed by chance; therefore sensitivity to forest height changes from interferometric pair to interferoimetric pair. In this study 6 interferometric X-band acquisitions were investigated for their practicability to estimate forest heights. Data were acquired in a Dual Pol Stripmap mode. For data quality estimation interferometric coherence was calculated. The main factor affecting interferometric coherence is temporal decorrelation, being the dominant decorrelation source in all acquistions. For an outlook an optimum acquisition scenario, excluding temporal decorrelation, was derived which can be used for a single pass acquisition as could be provided by the future mission TanDEM-X.
Alicja Koscz "Optimierung der Parameter einer P-Band Gruppenantenne für elektrisches Beam-Pointing"
Dienstag, 26. Januar 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Das F-SAR wird mit zwei P-Band Frequenzbereichen ausgestattet. Da im Bereich 300 - 400MHz nur eingeschränkt Daten gesammelt werden können und sich dieser Frequenzbereich nicht mit z.B. BIOMAS deckt, wird ein erweitertes P-Band System im Bereich 410 - 460 MHz aufgebaut.
Im Rahmen einer Studienarbeit wurden die Grundlagen für die neue Antenne erarbeitet. Der Vortrag befasst sich mit der Entwicklung eines Einzelelementes und Vorstudien für eine Gruppenantenne im Frequenzbereich 435 MHz / 50 MHz Bandbreite. Dabei liegt der Fokus in der Gewichtsoptimierung der Struktur unter den Randbedingungen die durch das existierende P-Band System vorgegeben werden (Größe / Windabweiser, Befestigungspunkte,..).
Das Element ist für den Einsatz in einer phasengesteuerten Gruppenantenne mit großen Schwenkwinkeln angepasst. Vorgeben sind die Blickrichtungen + - 42° Grad off nadir sowie nadir-Blickrichtung, für den Einsatz als Sounder. Für diese drei Richtungen ist die Gruppenantenne hinsichtlich Phasen- und Amplitudenansteuerung untersucht worden. Die sich ergebenden Diagramme für die Gruppenantenne bilden den vorläufigen Abschluss der Arbeit.
Dr. Christian Beine "Theoretische und experimentelle Untersuchungen zu einem vollpolarimetrischen, breitbandigen Mehrfrequenz-Radarsystem mit synthetischer Apertur für komplexe Szenarien"
Montag, 25. Januar 2010
14:00 Uhr s.t. Großer Besprechungsraum HR, Gebäude 102
Abstract:
Eine genaue und präzise Abbildung der Erdoberfläche ist heute ein universelles Verfahren der Informationsgewinnung sowohl für das Militär als auch zivile Organisationen. Mikrowellensysteme erfassen die charakteristischen Rückstreueigenschaften der abzubildenden Szene bei verglichen zur Optik großen Wellenlängen. Dabei sind aktive Systeme mit eigener Beleuchtung der Zielszene nahezu unabhängig von der Tageszeit und dem Ort der Beobachtung. Mikrowellen durchdringen die Atmosphäre mit ihren Wetterphänomenen deutlich besser als Licht und sind dadurch auch bei unsichtigen Wetterlagen einsetzbar.
Zunehmend höhere Anforderungen in der Mikrowellen-Fernerkundung verursachen einen Trend zu höheren Auflösungen. Ein hoher Detaillierungsgrad der Aufnahmen ermöglicht über die reine Detektion von Einzelzielen hinaus zumindest seine Klassifikation oder sogar seine Identifikation. Gegenwärtige Radarsysteme ziviler Nutzung liefern in der Regel Auflösungen im Bereich bis zu 1m oder leicht darunter, militärisch verwendete Systeme stoßen in Bereiche mit noch deutlich höheren Auflösungen vor.
In dieser Arbeit ist ein höchstauflösendes, kohärentes Radar für Abbildungen sowohl nach dem SAR-Verfahren als auch nach dem ISAR-Verfahren entwickelt und aufgebaut worden. Das mit dem Namen UniRad benannte System ist durch seine universelle Konstruktion in einem breiten Anwendungsspektrum einsetzbar. Dabei liegt besonderes Augenmerk nicht nur auf der extrem hohen Auflösung des Radarsystems in Entfernungs- und Azimutrichtung, sondern auch auf der Möglichkeit, Messungen in verschiedenen Frequenzbändern durchzuführen. Um eine Entfernungsauflösung im Zentimeterbereich zu erreichen, arbeitet UniRad mit Bandbreiten bis zu 4GHz und kann dabei im L-/ S-, C- X- oder Ku-Band betrieben werden.
Um die Leistungsfähigkeit zukünftiger operativer Radarsysteme anhand hochauflösender Bilder aufzuzeigen, ist es nötig, mit einem Experimentalradar bereits jetzt Bilder mit Auflösungen im Zentimeterbereich bereitzustellen. Für diese hohen Auflösungen ist der Aufbau des in dieser Arbeit entwickelten Radarsystems UniRad als Präzisionsmessgerät unumgänglich. Mit Unirad können bisher noch nicht beobachtbare Abbildungseffekte erforscht werden und weitaus detailliertere Signaturen höchster Auflösungen von relevanten Zielen erzeugt und somit erst untersucht werden, als es mit den bisherigen Radarsystemen möglich war. Durch seine Universalität kann das entwickelte UniRad für den Einsatz als bodengestütztes Seitensichtradar auf einem schienengebundenen Trägersystem bewegt werden. Für die Signaturerfasssung kann es als Radar zur Vermessung von Objekten auf einer rotierenden Plattform im inversen SAR-Modus (ISAR) betrieben werden.
Im Vortrag werden das Radarsystem und seine Eigenschaften vorgestellt. Mögliche Fehlereinflüsse werden per Simulation illustriert. Messergebnisse und deren Güte werden anhand von Punktzielen und komplexen Szenarien demonstriert und diskutiert.
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