Ulrich Balss

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Michael Eineder

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Helko Breit

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Christoph Gisinger

Hospital of the Brothers of St. John of God

Thomas Fritz

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Steffen Suchandt

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Hartmut Runge

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Stefan Hackel

Clinical Research Consortium

Xiao Ying Cong

Technical University of Munich

Marie Lachaise

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Xiaoying Cong

Dornier Flugzeugwerke (Germany)

Cooperative Institutions

Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

Technical University of Munich

Remote Sensing Solutions (Germany)

Federal Agency for Cartography and Geodesy

Dienstleistungszentrum Ländlicher Raum

ORCID

European Space Astronomy Centre

University of Bremen

Polytechnic University of Turin

Friedrich-Alexander-Universität Erlangen-Nürnberg

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Geodetic Stereo SAR - 4-D coordinate retrival of persistent scatterers from TerraSAR-X radar observations

Christoph Gisinger Stefan Gernhardt Stefan Auer Ulrich Balss Stefan Hackel

The combination of geodetic principles for correcting radio signals with spaceborne Synthetic Aperture Radar (SAR) has led to a new type of accurate radar observations. This approach is comparable to satellite altimetry or Global Navigation Satellite Systems (GNSS), where errors in the signal time-of-flight caused by the Earth’s atmosphere and the geodynamic effects (solid Earth tides, ocean loading, …) are removed by external models or complementary observations. In case of the radar satellites TerraSAR-X and TanDEM-X, the possibility of such geodetic SAR observations was demonstrated by using several radar corner reflectors with known reference coordinates. Their positions were retrieved not only in the 2-D radar geometry (range, azimuth) but also in absolute 3-D with an accuracy of 1-2 centimeter (1 sigma level). Moreover, additional velocity determination has become possible if the radar data has sufficient temporal coverage. After the successful demonstration for radar corner reflectors, the concept of geodetic stereo SAR shall now be applied to opportunistic persistent scatterers (PS) found in SAR images acquired in urban areas. TerraSAR-X data covering several years are available for the city of Munich and our general aim is the usage of geodetic stereo SAR to retrieve both the global coordinates of the PS as well as their common velocity vector linked to plate tectonics. Like in the case of the corner reflectors, a controlled test scenario has been established by selecting a building of Technische Universtat Munchen (TUM) which provides a large set of PS clearly visible in the radar images. A detailed and geometrically accurate model of this building was created in the global reference frame, and analysed by ray tracing methods to verify the 3-D PS positions obtained from SAR. Regarding the secular velocity, permanent GNSS operated at TUM campus enables a reliable cross-comparison with the SAR-based solution. Our presentation gives insight into the methods and the results achieved for the TUM test scenario. In future, geodetic stereo SAR shall enable the straight forward integration of SAR observations into GNSS networks and support the observation of secular deformations like plate tectonics or post glacial rebound.

Corner reflector

Source

Cite

Citations (0)

Analysis of internal timings and clock rates of TerraSAR-X

Ulrich Balss Helko Breit Thomas Fritz Ulrich Steinbrecher Christoph Gisinger

Due to the indirect measurement principle of radar on base of signal travel time, a very precise calibration of the sensor's internal clock with regard to clock rate and potential time offsets relative to the Coordinated Universal Time is an essential prerequisite for accurate pixel localization in Synthetic Aperture Radar. Giving special considerations on this aspect, we developed two algorithms that improve the already high localization accuracy of TerraSAR-X: The either one very precisely determines the true oscillator clock rate, while the other one effectively refines the accuracy of time annotation. Experimental analyses evaluate the obtained improvements in localization accuracy from both techniques.

SIGNAL (programming language)

10.1109/igarss.2014.6947024

Cite

Citations (19)

Space Borne SAR Traffic Monitoring

Hartmut Runge Steffen Suchandt Alexander Kotenkov Helko Breit Martin Vonavka

The need for world wide traffic monitoring with remote sensing means is described. The pros and cons of air borne and space borne sensor platforms are compared for this application. First results of automatic detection of moving objects in a TerraSAR-X scene are presented.

Source

Cite

Citations (6)

A Satellite On-Board SAR Processing Chain for Generation of Rapid Civil Alerts

Stefan Wiehle Dominik Günzel Björn Tings Helko Breit Ulrich Balss

On board

Source

Cite

Citations (0)

High precision measurement on the absolute localization accuracy of TerraSAR-X

Ulrich Balss Xiao Ying Cong Ramon Brcic Moritz Rexer Christian Minet

The German SAR (synthetic aperture radar) satellites TerraSAR-X (TSX-1) and TanDEM-X (TDX-1), launched in June 2007 and June 2010 respectively, provide an unprecedented geometric accuracy. Previous studies showed an absolute pixel localization for both sensors at the centimeter level [4] [5] [6]. However, recent measurements show that in range, under extraordinary good conditions, a location accuracy of even a few millimeters seems to be attainable. While on a long-term scale, we observed a slow variation of subsequent measurements; on a short-term scale, they coincided to within a few millimeters. The measurement series will be continued. The cause of the long-term variation is the subject of current investigation.

10.1109/igarss.2012.6351217

Cite

Citations (27)

Evaluation of ESA's Extended Timing Annotation Dataset (ETAD) for Sentinel-1 - First Results for Ice Velocity Monitoring and InSAR Applications in Greenland, Iceland and Norway

Christoph Gisinger Thomas Nägler Ludivine Libert Petar Marinkovic Yngvar Larsen

SAR images benefit from excellent geometric accuracy due to accurate time measurements in range and precise orbit determination in azimuth. Moreover, the interferometric phase of each single pixel can be exploited to achieve differential range measurements for the reconstruction of topography and the observation of earth surface deformation and surface motions. But these measurements are influenced by the spatial and temporal variability of the atmospheric conditions, by Earth dynamics, and by SAR processor approximations, which may lead to overall displacements shifts of up to several meters. These effects become visible in various SAR applications including the retrieval of ice velocity applying offset tracking and various InSAR applications, which might require several post-processing steps and external information for correction. In this paper we present the Extended Timing Annotation Dataset (ETAD) for Sentinel-1 recently developed in a joint effort by ESA and DLR based on research results and processor prototypes available at DLR.

Earth observation

Source

Cite

Citations (1)

Potential of Global SAR Positioning for Geodetic Applications – Lessons Learned from TerraSAR-X and Sentinel-1

Christoph Gisinger Martin Willberg Ulrich Balss Stefan Hackel Michael Eineder

With our implementation of geodetic techniques for data processing and data corrections, spaceborne Synthetic Aperture Radar (SAR) has attained the possibility of fixing global positions of dedicated radar points at the low centimeter accuracy level. Such points can be created by passive radar corner reflectors, and the positioning method relies on the inherent ranging capabilities of SAR sensors. Thus, we may refer to the method as SAR imaging geodesy or geodetic SAR. Determining accurate long-term global positions of objects on the Earth’s surface is typically associated with Global Navigation Satellite Systems (GNSS) and one of the core elements of modern space geodesy. In order to do so, high-grade geodetic equipment with constant power supply, as well as the possibility for data transfer are required, limiting dense application on a large scale and poses difficulties for very remote areas with little or no infrastructure. Whereas certain regions like Japan or the San Andreas Fault are densely covered by GNSS such coverage may not be achievable everywhere on the globe. To improve the situation, we present a concept of jointly using SAR and GNSS for expanding geodetic positioning to applications requiring long-term coordinate monitoring. In future, the use of cost-effective passive reflectors in X-band SAR or low-cost battery-powered active transponders, which are currently in development for C-band SAR, could provide global coordinates anywhere where SAR imagery is acquired under multiple incidence angles. The main requirements are precise orbit determination, processing of the SAR imagery omitting geometric approximations, as well as the rigorous correction of perturbations caused by atmospheric path delay and signals of the dynamic Earth. If a reflector or transponder already has known reference coordinates, e.g. from co-location with GNSS, the perturbing signals can be mitigated for the surrounding radar points by applying differential SAR positioning techniques similar to differential GNSS, provided that all the points are included in the same radar image. In this contribution we discuss the geodetic SAR methods with respect to our experiences gained with the TerraSAR-X mission, and present first results of experiments carried out with Sentinel-1 data.

Earth observation

Source

Cite

Citations (0)

Absolute 4-D positioning of persistent scatterers with TerraSAR-X by applying geodetic stereo SAR

Christoph Gisinger Stefan Gernhardt Stefan Auer Ulrich Balss Stefan Hackel

The paper describes the direct retrieval of global coordinates of persistent scatterers (PS) including their secular displacement by plate tectonics from Synthetic Aperture Radar (SAR). For this purpose we combine stereo SAR methods, least squares parameter estimation, and geodetic observation corrections. The procedure is based on our previous research with TerraSAR-X and now applied for PS situated on the facade of a building of Technische Universität München (TUM). In order to verify the PS-based solution, we have created an accurate building model with global coordinates suitable for SAR simulations, and we use the results of permanent Global Navigation Satellite Systems (GNSS) to validate the displacement rates. Our preliminary results for the simulated phase centers and stereo SAR already indicate similar phase centers on the building facade, and the displacement rates could be retrieved with mm/year accuracy.

10.1109/igarss.2015.7326444

Cite

Citations (6)

First results of ground moving target analysis in TerraSAR-X data

Steffen Suchandt Hartmut Runge Michael Eineder Helko Breit Alexander Kotenkov

Summary form only given. The advanced high-resolution German SAR satellite TerraSAR-X is scheduled to be launched at the end of May 2007. Due to its daylight and weather independent applicability in combination with a large spatial coverage and a short acquisition time, SAR has become a promising tool for traffic monitoring in recent years. Ground moving target indication (GMTI) techniques shall be applied to TerraSAR-X data in order to demonstrate the capability of a space borne SAR sensor to monitor traffic flows on highways. A series of GMTI experiments were to be carried out during the commissioning phase of the TerraSAR-X satellite. In first trials, cars, which are equipped with special radar reflectors and GPS receivers, were to be used as moving target references that are imaged in TerraSAR-X data takes. In a follow on experiment, arbitrary cars on motorways were to be imaged simultaneously by TerraSAR-X and by an airborne high-resolution camera. Car tracks extracted from the series of the optical images shall serve as a reference for the evaluation of the TerraSAR-X moving target data in this case. The paper presents first results of the data evaluation. An experimental GMTI processing system is used to detect and measure moving targets in both single-channel and dual-channeldata. The dual-channel data, which enable the application of well established GMTI methods like the along-track interferometry (ATI) or displaced phase centre array (DPCA) techniques, are acquired either in the so-called "aperture switching" mode with virtual multiple receiving channels or in the dual-receive antenna (DRA) mode with physically separated receiving channels. The paper reports on the analysis of the first experimental GMTI data by using different detection and measurement strategies. This includes the adapted processing of the SAR raw data with respect to the moving target signals, the incorporation of GIS data in the detection and measurement process and the application of different detectors for across- and along-track velocity components of the moving cars. The quality of the data is thoroughly analyzed and conclusions are drawn for the development and the performance of a fully automatic GMTI processing system for TerraSAR-X. Furthermore, an outlook on the planned experiments is given.

Moving target indication

10.1109/igarss.2007.4423710

Cite

Citations (9)

TerraSAR-X SAR Payload Data Processing: Results from Commissioning and Early Operational Phase

Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on (2008)

Helko Breit Thomas Fritz Birgit Schaettler Ulrich Balss Heiko Damerow

TerraSAR-X, the first national German radar satellite, was launched in June 2007. It carries an X-band highresolution synthetic aperture radar instrument featuring the operational imaging modes Stripmap, ScanSAR and, particularly, Spotlight in a variety of different polarization modes. The TerraSAR-X mission completed its commissioning phase in December 2007 and started the provision of high-resolution products from advanced SAR modes for both the scientific and commercial user community from January 2008 on. The payload ground segment (PGS) is responsible for the reception of the SAR payload data, their archiving and processing and the distribution of the generated SAR basic products to users. From the first mission day on, PGS was operated successfully using both its request workflow starting with the input of user orders and ending with the delivery of the generated product and its operational SAR data workflow for the reception and processing of the SAR payload data. The central part of PGS is the TerraSAR Multi-Mode SAR Processor (TMSP) focusing the SAR data in a unified way for the different imaging configurations. A wide range of processing options spanning from phase preserving complex products in slant range geometry to orthorectified terrain corrected intensity images lead to a comprehensive collection of SAR product types and variants. Together with instrument calibration, checkout and tuning of the SAR processor was one of the major tasks of the commissioning phase with respect to product verification and validation. This paper summarizes the key activities and exposes the achievements obtained with respect to focusing quality.

Payload (computing)

Ground segment

Early-warning radar

Data Processing

Source

Cite

Citations (9)