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Vorträge im Institutsseminar 2011
Gianpaolo Massaroli “Crop Volume Characterisation using Dual Polarimetric SAR in X-band”
Montag, 19. Dezember 2011
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In agriculture the management practice using precision farming is becoming a standard. The idea behind is a farming management concept based on an optimized field-level management and it relies on new technologies like agricultural satellite monitoring systems, information provision and geospatial tools. Polarimetric SAR is an ideal monitoring tool to deliver important physical parameters over the whole crop cycle and the derived information can be used for precision farming. The main research purpose is to investigate dual polarimetric TanDEM-X data (HH/VV) for their potential to characterize crop volumes in terms of particle shape and volume orientation. Analyses are carried out for the whole growth season in order to enable first insights into dual-polarimetric X-band scattering of agricultural vegetation volumes. For this reason a time series from April until the end of July 2011 was recorded for the agricultural test site of Wallerfing (Lower Bavaria, Germany). Simultaneously to the overflights, in situ measurements were conducted by DLR and Ludwig-Maximilians-University (LMU) for three different crop types (winter wheat, winter rape and summer corn) to characterize the crop status and the soil conditions. In the beginning of the investigations simple correlations between PolSAR descriptors, like the polarimetric entropy, and the measured vegetation parameters, such as crop height, leaf area index and phenology, have been analyzed to retrieve qualitative information on the crop status. For quantitative analysis, a physically-based particle scattering model is applied for inversion of the volume orientation and the particle shape. The results reveal that the presence of ground scattering is quite distinct in X-band, even on later dates in the growing season. This biases the estimation of the vegetation parameters. Hence, first attempts were made to remove the ground scattering contribution for an improved vegetation analysis.
Vittorio Bianco “Phase Calibration of Multibaseline SAR Data Stacks”
Dienstag, 13. Dezember 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
New opportunities are arising in earth observation with the use of multibaseline (MB) SAR being able to combine data stacks for an improved imaging and characterization of the observed scene. Prior to any MB coherent processing, it is necessary to correct the data stack for the phase contributions due to residual non-compensated platform motions (typical in airborne SAR applications) and/or atmospheric propagation delays (e.g. in spaceborne SAR), which in general are different from track to track. The classical calibration methods tackle the MB phase calibration problem by means of the detection of point-like scatterers. However, the effectiveness of these techniques is scenario-dependent, as both the number and spatial distribution of such scatterers varies. Especially in natural scenarios, the MB phase calibration is particularly challenging given the volumetric nature of the scattering. Moreover, a limited number of baselines can impair the detection performance, which in turn results into a degraded calibration quality. In this work we propose a new calibration method based on the minimization of the entropy applied on the vertical profile of the backscattered power to improve the performance. This allows to potentially exploit the MB SAR signal independently of the imaged scattering mechanism. With particular reference to SAR Tomography applications, the proposed method has been tested under controlled conditions by processing a simulated dataset of a forest stand. Performance results are shown in this presentation. The calibration accuracy has been also evaluated with an airborne L-Band dataset acquired by the DLR E-SAR platform over the forest site of Traunstein (Germany), and comparisons with the classical calibration techniques have been carried out.
Junghyo Kim "Multiple-Input Multiple-Output (MIMO) SAR for Multimodal Operation"
Mittwoch, 30. November 2011
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
As expanding utilities of SAR data in various fields, capabilities of frequent monitoring, wide coverage and high geometric resolution become more important issues in a technical sense. Moreover, an adaptive system concept for diverse data acquisition modes is strongly desired. State-of-the-art SAR sensors however do not satisfy those demands at the same time. Based on two core techniques: digital beamforming (DBF) and orthogonal waveform, this work aims at establishing a novel Multiple-Input Multiple-Output (MIMO) SAR system concept to overcome the modern SAR performance and to satisfy the demands in a wide range of applications. The main contribution of the present work is to establish a novel multimodal operation concept and to develop a new waveform scheme. In this presentation, a novel orthogonal waveform scheme based on Orthogonal Frequency Division Multiplexing (OFDM) technique is introduced. For dual transmit antennas, this presentation shows the exploitation of orthogonal property of subcarriers to produce multiple orthogonal waveforms and the demodulation technique of these waveforms. For the experimental verification of the core techniques and the system concept, a laboratory experimental system is developed. This presentation also exhibits the hardware design issues to accomplish successful experiments and the developed system aspects as well as experimental results.
Luis Gustavo Pereira Vicente "Correlating SAR: Concepts and Simulation"
Donnerstag, 20. Oktober 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
As it is well known, SAR systems rely on targets staying coherent during the integration time so that a synthetic aperture can successfully be constructed. Fast decorrelating targets appear, therefore, defocused in azimuth. The Correlating SAR (CoSAR) concept is presented as an alternative technique to overcome this limitation. This alternative technique is inspired in the aperture synthesis techniques used by some imaging radiometers, like MIRAS on the SMOS mission. CoSAR operation concept is to first estimate the azimuth spatial cross-correlation by combining the radar echoes received by two systems moving in opposite directions, and then applying the equivalent to a matched filter to this cross-correlation function. This work presents and illustrates, by means of computer proof-of-concept simulations, the CoSAR concept.The simulations produced by the program show the difference between the results of basic SAR processing and CoSAR image, and highlight some fundamental trade-offs.
Noora Al-Kahachi "Polarimetric Characterization of Two Layer Structure"
Dienstag, 18. Oktober 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
One of the challenges of future SAR missions will be the estimation of surface and subsurface geometric and dielectric characteristics. An example of two-layer structures is a frozen lake, where the upper layer consists of ice and the lower one is water. The ice water interface provides high reflectivity for the electromagnetic wave because of the strong dielectric contrast between the two media. For some of the shallow subarctic lakes the water interface disappears since the lakes freeze in winter to the bed. Therefore lakes are good candidates for evaluating SAR Polarimetric capabilities in subsurface probing. For this L-Band full Polarimetric ALOS(PALSAR) data are used in this research. A scattering model for volume, subsurface, and the interaction between them and evaluation of polarimetric SAR data using this model will be presented.
Arthur Antonello "Implementation of Compressed Sensing Algorithms in Python"
Dienstag, 11. Oktober 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Compressed Sensing (CS) is an emerging sampling paradigm that has recently proved to be an effective approach to polarimetric SAR tomography. This work focuses on the practical implementation of CS reconstruction algorithms via convex optimization. Specifically, we used the Python programming language and implemented a second order cone program (SOCP) that deals with multiple looks as well as multiple polarizations simultaneously. Also, special consideration was given to handling complex data appropriately. Finally, the methods will be validated by using airborne data acquired by the E-SAR sensor of DLR.
Kevin Eyssartier "Monitoring the Petermann Ice Island using TanDEM-X Satellites"
Dienstag, 30. August 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In August 2010, the head of one of the biggest glacier on Earth, the Petermann glacier located in Greenland, broke into a 250km² Iceberg.
It travelled at a fast pace into the Nares strait and turned into an ecological warning.
The goal of this project was to study the evolution of this iceberg, and in particular to study the changing topography due to melting and calving using a time-series of TanDEM-X interferometric Synthetic Aperture Radar (SAR) image processing data. The main challenge to be addressed in the context of this project was the large scale motion of the glacier, including drifts (translation) and rotations, which had to be estimated and compensated in order to work on a reference system tied to the Iceberg.
These challenges have been addressed combining techniques rooted in InSAR processing (such as block correlations) and Image Processing methods, such methods such as region growing or the Radon transform.
This presentation will describe in detail the processing flow, with an emphasis on steps not required in typical stacks processing, and present some preliminary results.
Claudia Hilbert, Nicolas Ackermann, Tanvir Ahmed Chowdhury and Nicole Richter "3 PhD presentations from the Department for Earth Observation, University Jena"
Dienstag, 19. Juli 2011
10.30 h Großer Besprechungsraum HR, Gebäude 102
Claudia Hilbert "Derivation of forest structure using satellite, multifrequent radar and lidar data in Thuringian Forest, Germany"
Abstract:
The global forests play a critical role in the global carbon cycle but many issues regarding their functioning as carbon sinks and source are still poorly understood. Therefore detailed spatial information about the extent and three-dimensional structure of forests are needed. The synergy of pointwise lidar and multifrequent SAR data is a promising approach in this context. The study presented here uses ALOS PALSAR, TerraSAR-X and ICESat/GLAS data to derive forest height and biomass as main parameters for forest mapping in Thuringian Forest, central Germany. Several additional data sets like a forest inventory data base and airborne laser scanning (ALS) data are available for calibration and validation of the remote sensing data. Since the test site is a lower mountain range, the influence of the terrain topography on the remote sensing data is a main issue of the research.
The presentation will introduce the basic concept and the current status of the study. Some results regarding the different parameters described from the SAR data, i.e. intensity, coherence and texture, will be discussed. The SAR data are intended to provide information about the horizontal structure and the biomass of the forest. The focus of the second part of the presentation will be on the GLAS analysis. An approach to extract tree height from the GLAS waveforms based on the ground peak will be shown. The algorithm to define the ground peak will be assessed by comparing the GLAS surface elevation with the ALS based Digital Elevation Model (DEM). The GLAS tree height will be investigated with respect to reference heights extracted from the inventory and the ALS data sets. Finally, the influence of the surface topography on the waveform structure will be investigated and some waveform examples will be presented more in detail. The results of the GLAS analysis will provide a direct tree height measure. Thus, they will be an important input for a robust algorithm to retrieve forest structure by using SAR and lidar data.
Tanvir Ahmed Chowdhury "Forest Structural Parameters and Growing Stock Volume Retrieval in Thuringian Forest using L-band Polarimetric Radar"
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 saturation level of the radar backscatter is quickly achieved, despite further increases of GSV. To avoid this effect, polarimetric technique 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 sensor over the thousands of forest stands in Thuringian Forest, central part of Germany, 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, different types of species and dominant species of composition, tree volume, relative stocking were measured of these large forest stands. Investigation 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. The relationship between polarimetric parameters and GSV can be initially described using simple and multiple regression models. Further forest parameters to be implemented in this study are tree height, tree diameter, tree age, relative stocking, and tree species.
Nicolas Ackermann "Evaluation and modeling of Optical and SAR spaceborne sensors for stem volume retrieval over Germany’s low mountain range forested areas"
Abstract:
The aim of this research is to demonstrate the potential of optical and SAR satellite imagery for the retrieval of forest biophysical parameters and in particular forest Growing Stock Volume (GSV). The Thuringian Forest has been chosen for the investigations. The forest, located in the center of Germany, is well known for its low mountain range temperate regions mostly covered by Norway Spruce species. The available ground data consists of a forest inventory delivered by the local forest offices. The latter includes forest parameters such as stand height, basal area, DBH, stem volume or tree species composition. The satellite remote sensing data are composed of SAR and Optical sensors. L-band is distinguished by ALOS PALSAR while X-band frequencies are given by TerraSAR-X and Cosmo-SkyMed. RapidEye and Kompsat2, both high resolution multispectral systems, are completing the spaceborne datasets. The presentation will be divided into three different topics. Firstly, the Thuringian forest being characterized by frequent hilly regions, some topographic normalization issues of the SAR signal by considering aspect and slope information will be addressed. Secondly, a focus on the evaluation of the SAR and optical data will be given. The understanding of the scattering and forest decorrelation mechanisms occurring on the test site will be underlined as well as the physical processes occurring in the visible and infrared spectrum range. To this end, weather effects such as precipitation, temperature and wind, which most particularly affect the SAR signal will be taken into consideration. Lastly, a description of GSV retrieval using L-band multitemporal interferometric coherence will be given. Preliminary quantitative assessments using the Root Mean Square Error (RMSE) have been performed. The results showed an accuracy reaching 75 [m3/ha]. The presented results will serve as a foundation for the fusion of SAR and optical satellite imagery and more specifically for the development of more accurate and, above all, more robust retrieval algorithms.
Nicole Richter "Surface Deformation of Kīlauea Volcano, Hawai‘i, from TerraSAR-X Interferometry"
Abstract:
Nearly all volcanic eruptions are accompanied by measurable changes in the physical and chemical state of the volcanic system. Surface swelling, for example, is a characteristic expression of subsurface magma accumulation and is therefore an excellent indicator of potential future volcanic activity. Here, TerraSAR-X interferometry was applied to identify and analyze volcano-wide deformation of Kīlauea Volcano, Hawai’i, during June 2008 to early 2011. Pre- and co-eruptive TerraSAR-X interferograms of the Kamoamoa eruption (March 5, 2011) have been produced. Results have been compared to ENVISAT interferograms (only available until October 2010, when a change in ENVISAT’s orbit compromised the quality of derived InSAR data for Hawai`i) and GPS time series, both of which agree with the TerraSAR-X InSAR results. In comparison to ENVISAT, the TerraSAR-X data have the advantage of very high resolution (pixel size of about 3 m compared to 30 m for ENVISAT) and a repeat cycle of only 11 days (compared to 35 days for ENVISAT). The latter characteristic allowed for the interpretation of net deformation associated with short-term (i.e., hours to days) deflation-inflation cycles of Kīlauea’s summit magma reservoir. With the availability of a very high-resolution LIDAR DEM of Kīlauea’s summit to correct for topography, it is also possible to make use of the satellite’s high spatial resolution. Interferograms with 3 m pixel resolution provide information on instability of the summit eruptive vent, which has the potential to forecast collapses that lead to vent growth and occasional explosive events. These results could not be achieved with lower spatial and temporal resolutions, demonstrating the excellent prospects for continued use of TerraSAR-X as an operational volcano monitoring and research tool.
Octavio Ponce Madrigal "Fast Factorized Back Projection for Circular SAR"
Dienstag, 12. Juli 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Circular SAR (CSAR) has become of more interest in the SAR community. Unlike Stripmap, ScanSAR and Spotlight modes, CSAR has the capability to get measurements over 360°. Thus, it has the potential to obtain high resolution images (up to ≈ λ/4), as well as tomographic information for 3D reconstruction. Due to the non-ideal motion of the platform and large observation times, only time-domain approaches result in high quality focused data. Therefore, the large amount of data involved result in a bottle-neck and a huge computational burden, especially for the direct Back Projection (BP) algorithm. The Fast Factorized Back Projection (FFBP) algorithm for circular tracks improves significantly the computational burden, while at the same time considering the topographic changes and the real flight track with high accuracy. To further accelerate the process this algorithm was implemented also on a Graphics Processor Unit (GPU). Fully polarimetric data, acquired by the DLR’s E-SAR system, was focused with this method to the theoretical limit of ≈ λ/4, hence the efficiency, accuracy and performance of the circular FFBP are demonstrated, as well as the potential of CSAR when focusing over 360°.
Dr. Pekka Alitalo "Realization of broadband electromagnetic cloaking devices"
Dienstag, 28. Juni 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Recently the topics of electromagnetic cloaking and invisibility have attracted significant interest in the scientific community. The advances in the areas of metamaterials and transformation-optics have made it possible to realize materials and devices that can guide electromagnetic waves around an object so that the total scattering cross section of this object can be made very small, ideally zero. This means in practice that the object is made "invisible" to the impinging electromagnetic radiation and therefore undetectable. The transformation-optics approach usually employs resonant metamaterials to achieve exotic wave propagation characteristics that are required in cloaking. However, these devices often suffer from extremely narrow operation bandwidth and high complexity of the structure. This presentation gives an overview of the most important cloaking techniques and shows how simple waveguiding structures can be used to realize broadband, low-loss cloaking devices at microwave frequencies.
Esteban Pedro Aguilera "Compressed Sensing for Polarimetric SAR Tomography"
Dienstag, 14. Juni 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
In recent years, three-dimensional imaging by means of SAR tomography has become a field of intensive research. In SAR tomography, the vertical reflectivity function for every azimuth-range pixel is recovered by processing data acquired from a special tomographic imaging geometry. The most common approach is to generate a vertical synthetic aperture in the elevation direction through imaging from a large number of parallel tracks. This imaging technique is appealing, since it is very simple and applicable in the space-borne case, but has the drawback that it is considerably time consuming when only one or a few sensors are available.
In an attempt to reduce the number of parallel tracks, a new tomographic focusing approach is proposed, that trades number of SAR images for correlations between neighboring azimuth-range pixels and polarimetric channels. As a matter of fact, this can be done under the framework of Distributed Compressed Sensing (DCS), which stems from Compressed Sensing (CS) theory.
Results will be validated by using fully polarimetric L-band data acquired by the E-SAR sensor of DLR, thus demonstrating the potential of the DCS methodology.
Francesco DeZan "Coherent Stacking of SAR Images for Efficient Interferometric Processing"
Dienstag, 31. Mai 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The estimation of the interferometric phases from stacks of SAR images is not as straightforward as with single interferograms. A Cramér-Rao bound for the phase estimation for stacks has been derived and an efficient estimator is available too, however its computational cost might be too high for large-scale processing tasks. With a limitation to the number of interferograms that can be processed, the natural choice seems to be to select the most coherent among them, but that is not the right thing to do in all cases. This presentation intends to explain theoretically why it is so and what we can do in such cases. It is proposed to stack images instead of interferograms. The idea is that a filtering operation (coherent summation along time) can enhance the scatterer components which are coherent in the long term and yield interferograms with high coherence. The stable components of the targets --when present-- are the backbone of the interferometric performance and --if isolated-- do not need to be frequently sampled (hence the data and computational reduction). Some simulations along with some results for X and L-band data will be presented.
Rainer Tritz-Floßdorf, Leiter Schutzrechte und Lizenzen "Patente und Urheberrechtsschutz – ein Überblick"
Dienstag, 24. Mai 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Der Vortrag gibt einen kurzen Überblick zu den folgenden Fragestellungen:
- Was sind Patente?
- Wofür sind sie nützlich?
- Was sind die Voraussetzungen für die Erteilung eines Patents?
- Wie sind die Verfahren zur Erlangung eines Patents?
- Wie sind die DLR-internen Verfahren der Erfindungsmeldung?
- Was ist urheberrechtlich geschützt?
- Wie sieht es mit dem rechtlichen Schutz von Software aus?
- Ist Software patentierbar?
Maria José Sanjuan Ferrer "Contribution of Polarimetry for the CSs Detection in Ice with Full-Polarimetric TerraSAR-X Data"
Dienstag, 17. Mai 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The interest in using synthetic aperture radar (SAR) to study and monitor ice and glacier terrains for glaciological and climate change research has been increased in the last years. These natural objects are called distributed areas and are characterized by complex scattering mechanisms. Recently a technique to detect point-like scatterers called Coherent Scatterers (CSs) was developed and has shown its performance over urban areas using airborne data. Depending on employed polarization channel this technique enables the extraction of polarimetric based information from detected CSs. In this presentation, the potential of using CSs detection techniques over distributed areas, like glacier terrain, with wide-band TerraSAR-X data is investigated, using a new developed spectral correlation method: the Phase Variance Approach. Two test sites have been analysed: Glacier d'Argentière (France) and Aletschgletscher (Switzerland). The contribution of polarimetry will be presented and the problems derived from the new CSs detection method will be investigated.
Charles Deledalle - "Filtering of polarimetric SAR images based on non-local means"
Dienstag, 10. Mai 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Synthetic aperture radar (SAR) images provides reflectivity, polarimetric or interferometric informations, which are paramount to scene interpretation or low-level processing tasks such as segmentation and 3D reconstruction.
Interferences of elementary scatterers causes speckle effects on the measured backscattered waves. Due to speckle, the images are estimated in practice on local windows (known as multi-looking). These windows lead to biases and resolution losses due to local heterogeneity caused by edges and textures. During the past few years, non-local techniques have proved their efficiency for image denoising to reduce noise while preserving structures. These approaches assume there exist enough redundant patterns in images to be used for noise reduction. We suggest that the same assumption can be done for different modalities of SAR images. The proposed filter seems to deal well with the statistical properties of speckle noise and the multi-dimensional nature of such data. Results challenge/outperform other techniques.
Dr. Thomas Bahr "IDL 8.0 / ENVI 4.8 / SARScape 4.3 - Workshop"
Dienstag, 08. April 2011
09.30 h Großer Besprechungsraum HR (Raum 078), Gebäude 102
Abstract:
What’s New in IDL 8.0: New IDL 8 Graphics: Full batch & optional interactive usage, Very easy to annotate, print and save, High Quality Printing, direct PDF generation, New IDL 8 Language Features: New State of the Art Object Syntax, What’s New in ENVI 4.8 Full ENVI and ArcGIS Integration: Use ENVI directly within ArcGIS, Empower ArcGIS Models with ENVI+IDL, Advanced ArcGIS Mapping Tools in ENVI, Extend ENVI to the Enterprise: ENVI for ArcGIS Server, Deploy ENVI Tools to a Web Application, What’s New in SARscape 4.3 for ENVI, New Interferometry Stacking Module: Explore Persistent Scatterers and SBAS, New ENVISAT-ASAR atmospheric correction
Mehr
Rolf Hempel "Innovative Softwaretechnologie im DLR – Ein Überblick der Einrichtung „Simulations- und Softwaretechnik“ "
Mittwoch, 30. März 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Software ist zu einem wesentlichen Erfolgsfaktor in F&E-Projekten geworden. Ihre Entwicklung erfordert aufgrund wachsender Komplexität in zunehmendem Maße IT-Spezialkenntnisse. Die DLR-Einrichtung „Simulations- und Softwaretechnik“ beteiligt sich an der internationalen Softwareforschung und übernimmt anspruchsvolle Softwareentwicklungsaufgaben in Projekten mit anderen DLR-Instituten und externen Partnern. Sie ist an den DLR-Standorten Köln und Braunschweig vertreten. Das Spektrum der Themen und Projekte ist so vielfältig wie der Einsatz von Software in der heutigen Spitzenforschung. Es reicht von der Integration von Simulationsanwendungen in räumlich verteilte Softwaresysteme zur virtuellen Produktentwicklung, über die Visualisierung und das Management wissenschaftlicher Daten, über High-Performance-Computing bis zu eingebetteter Onboard-Software, zum Beispiel zur Lageregelung von Satelliten.
Aktuelle Software-Engineering-Verfahren werden in den eigenen Projekten eingesetzt und weiterentwickelt. Über das DLR-weite Software-Engineering-Netzwerk stellt die Einrichtung Entwicklungswerkzeuge und -techniken anderen Instituten zur Verfügung und schult deren Mitarbeiter in ihrer Anwendung. Die Einrichtung betreibt ein offiziell akkreditiertes Software-Testlabor.
Der Vortrag gibt einen Überblick der aktuellen Themen und Projekte der Einrichtung. Das Ziel ist die Identifikation des Kooperationspotentials zwischen HR und SC.
Frank Gumbmann "Millimeter Wave Imaging with an Optimized Sparse Periodic Array for Short Range Applications"
Dienstag, 22. Februar 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
The demand for millimetre wave (mmW) imaging techniques increases in the field of non-destructive testing (NDT) or security applications. The duration of the imaging process should be rather short. The imaging approach is a linear MIMO array that is linearly moved perpendicular to the antenna configuration. The mmW image is obtained by a digital beam forming (DBF) in array direction and SAR processing in along track. For a large MIMO array a high number of antenna elements are required to reach the spatial sampling rate, therefore an appropriate thinning concept is needed. A promising approach to reduce the total number of transmit and receive channels is a sparse periodic array (SPA) which offers an identical point spread function (PSF) compared to a dense array. The idea is to reduce the number of receive antennas, of a dense receive array, and enlarge the number of transmit antennas by the same factor. The resulting effective aperture, which is the convolution of the transmit and receive aperture function, is again a distribution of dense virtual antenna positions. Since the concept bases upon the effective aperture approach which is only valid in the farfield of the array, this approach will fail for short range applications. Thus the ambiguities which result from the under sampled receive array are not well suppressed. An extension of the sparse periodic array concept for short range applications on the basis of an optimized array design and an optimized beamforming algorithm is presented.
Tobias Rommel „Die Möglichkeiten von FM-CW-SAR bisherige Arbeiten und Ausblick in die Zukunft. Ein neues Radarexperiment für das DLR_School_Lab.“
Dienstag, 8. Februar 2011
10.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
FM-CW Radaren mit synthetischer Apertur wird immer mehr Beachtung geschenkt. Sie sind im Gegensatz zu gepulsten Systemen sehr leicht und äußerst kompakt. In Anbetracht dieser Tatsache wurde für das DLR_School_Lab ein eindimensional abbildendes Dauerstrichradar mit inverser synthetischer Apertur konzipiert und aufgebaut. Es soll Schülern in anschaulicher Weise die grundlegenden Prinzipien von SAR verdeutlichen.
Der Vortrag gibt einen kurzen Einblick in das bisherige Radarexperiment und stellt 2 Algorithmen beruhend auf kohärente Verarbeitung sowie signalangepasster Filterung (Matched Filter) zur Auflösung mehrerer, in Azimut ausgerichteter, Ziele gegenüber. Im Anschluss wird ein Ausblick auf weitere mögliche Arbeiten in dieser Thematik an unserem Institut gegeben.
Astor Torano Caicoya "Biomass estimation as a function of vertical forest structure - Potentials and limitations for Radar and LiDAR"
Dienstag, 1. Februar 2011
14.00 h Großer Besprechungsraum HR, Gebäude 102
Abstract:
Forest biomass stock, spatial distribution and dynamics are unknown parameters for many regions of the world. Thus, a method capable of quantifying biomass by means of Remote Sensing (RS) could help to reduce these uncertainties. In this study we analyze the capacity to improve the estimation of above-ground biomass (AGB) with a new approach based on forest vertical structure and its potential to improve RS estimations. Height to Biomass allometry allows biomass estimations from remote sensing systems capable to resolve forest height (LiDAR and polarimetric SAR interferometry (Pol-InSAR)). However, this approach meets its limitations for forest ecosystems under changing conditions in density and structure. To improve biomass estimation accuracy, additional parameters need to be measured. Pol-InSAR and LiDAR allow getting, besides forest height, vertical backscattering profiles which are connected to forest vertical structure. In the present presentation, the connection between forest vertical structure and biomass will be evaluated for several test sites. Moreover, vertical backscattering profiles from short footprint airborne LiDAR and Pol-InSAR data and their potential to reconstruct vertical forest structure will be presented. Last results from airborne x-band data from the Kryclan forest test site will be also presented.
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