Ulrich Balss

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

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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

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Processing of bistatic TanDEM-X data

Helko Breit Thomas Fritz Ulrich Balss Andreas Niedermeier Michael Eineder

On June 21 ^st , 2010, the German radar satellite TanDEM-X was launched and successfully placed in an orbit approaching the TerraSAR-X satellite until both systems will fly in close formation and will establish the only available bi-static interferometer in space. The primary TanDEM-X mission goal is to generate a global Digital Elevation Model (DEM) with a relative point-to-point height accuracy of 2 meters for moderate terrain at 12 m posting. For that purpose interferometric SAR data will be acquired over a period of 3 years in parallel to the operational running TerraSAR-X mission. Systematic processing of SAR raw data to so-called Raw-DEMs is performed by one single processing system, the Integrated TanDEM Processor (ITP). The final global DEM is then calibrated and mosaicked by a second system, the Calibration and Mosaicking Processor (MCP). The scope of this paper is to present an overview of ITP functionalities and to summarize the first processing results.

Tandem

Data Processing

10.1109/igarss.2010.5653602

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Citations (19)

Towards Operational SAR Imaging Geodesy: An Extended Time Annotation Dataset for Sentinel-1 Image Products

Christoph Gisinger Steffen Suchandt Helko Breit Ulrich Balss Marie Lachaise

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The limits of spaceborne SAR geolocation: Can we attain the 1 cm level?

Christoph Gisinger Thomas Gruber Ulrich Balss Helko Breit Michael Eineder

Assigning precise coordinates to spaceborne 2-D SAR images is crucial when combining the data with other sources of geo-localized information like optical images, road networks or GIS data in general.The range-Doppler principle underlying the SAR images readily allows for direct geolocation of SAR products and the satellite providers have adjusted their processing chains by geometrical calibration to ensure geolocation at half of the product resolution or better. In the case of bright artificial point targets, however, geolocation may be carried out far beyond the average product resolution and it provides the key to an overall geometrical consistency across different products or even different SAR missions. To achieve this, all the elements involved in a SAR image acquisition - orbit determination, payload calibration, image processing, atmospheric path delay correction, solid Earth surface signal correction - have to be treated with meticulous care. In the framework of the ESA commissioned project Fiducial Reference Measurements for SAR Geometric Calibration and Performance Assessment (FRM4SAR), we have documented and tested these elements. Based on our experience gathered with Sentinel-1 and TerraSAR-X, we will demonstrate how this task can be solved down to the low centimeter level. Potentially, the range and azimuth coordinates of point targets could even become as accurate as 1 cm. Long-term stable corner reflectors (CRs) with accurately known reference coordinates enable verification and cross-comparison of the geolocation capabilities. Using our CR installations in Europe and the large CR array located at the Surat Basin, Australia, we address the crucial elements of accurate geolocation processing, and share our latest results for Sentinel-1 and TerraSAR-X. Particularly the CR array in Australia consisting of 40 individual CRs distributed across a large area allows for detailed spatial probing of SAR products which reveals the limitations in SAR processing employing common approximations. Tackling such shortcomings in the processing and agreeing on standards in correcting geometrical SAR observation opens new applications for spaceborne SAR and we hope that our findings with Sentinel-1 and TerraSAR-X will be of use to both ongoing and future SAR missions.

Geolocation

Payload (computing)

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Precise Orbit Analysis of TerraSAR-X - Possibilities and Restrictions

Stefan Hackel Oliver Montenbruck Christoph Gisinger Ulrich Balss Michael Eineder

Orbit (dynamics)

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Automatic Extraction of Traffic Flows Using TerraSAR-X Along-Track Interferometry

IEEE Transactions on Geoscience and Remote Sensing (2010)

Steffen Suchandt Hartmut Runge Helko Breit Ulrich Steinbrecher Alexander Kotenkov

Spaceborne synthetic aperture radar (SAR) offers great potential for the measurement of ground traffic flows. A SAR with multiple receiving apertures aligned in flight direction repeatedly images the same ground area with a short time lag. This allows for an effective detection of moving ground objects, whose range variation translates into an interferometric phase signal between the receiving channels. The high-resolution German SAR satellite TerraSAR-X offers several ways to create multiple along-track apertures. We exploit this to demonstrate satellite-based traffic-flow measurements using along-track interferometry (ATI) and Displaced Phase Center Array techniques. In this paper, we address the usage of different TerraSAR-X ATI modes for data acquisition and describe an automatic near-real-time processing chain for the extraction of traffic information. The performance of this TerraSAR-X traffic processor is significantly driven by incorporating a priori knowledge of road networks. We present examples of automatic traffic detection as well as empirical evaluations thereof using different kind of reference data.

10.1109/tgrs.2009.2037919

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Citations (129)

<title>Processing of TerraSAR-X payload data: first results</title>

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2007)

Helko Breit Ulrich Balss Richard Bamler Thomas Fritz Michael Eineder

TerraSAR-X is Germany's new radar remote sensing flagship. It carries an advanced high-resolution X-band SAR instrument. The key element of the system is the active phased array antenna nominally operated with a bandwidth of 100 MHz or 150 MHz and an experimental 300 MHz capability. The instrument's flexibility with respect to electronic beam steering and pulse-to-pulse polarization switching allows the acquisition of SAR data in Stripmap, Spotlight and ScanSAR imaging configurations in different polarization modes for a wide range of incidence angles. The mission is implemented in the framework of a public-private partnership between the German Aerospace Center (DLR) and EADS Astrium GmbH Germany and will provide high resolution SAR data products for commercial use and scientific exploitation. Processing of the payload data will be performed at DLR's Payload Ground Segment (PGS) for TerraSAR-X. 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. During the 5 months lasting commissioning phase the complete processing chain will be properly tuned and adjusted. The TMSP algorithms have to be configured, e.g. thresholds for calibration pulse analysis, estimation window sizes for SAR data analysis, parameterization of estimation algorithms. Also the configuration of product variants with respect to resolution and radiometric quality will be checked and refined. This paper shortly reviews the different imaging configurations and product variants and gives a report on the SAR processor checkout activities and presents the first results.

Phase center

Payload (computing)

Data Processing

10.1117/12.738066

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SAR ground control point identification with the aid of high resolution optical data

Sina Montazeri Xiao Xiang Zhu Ulrich Balss Christoph Gisinger Yuanyuan Wang

Only until recently, it has been demonstrated that absolute localization with centimeter accuracy can be achieved for manually matched Persistent Scatterer (PS)s from TerraSAR-X images acquired from cross-heading geometries [1]. This paper describes an automatic algorithm for absolute localization of natural PSs in SAR images, where the detection of potential PSs is aided by high resolution optical data. As the focus of the study is on urban area, the target detection part relies on identification of lamp posts using template matching. These targets are, most probably, the only ones visible in SAR images acquired from both ascending and descending orbits. Thus, the methodology includes identification of lamp posts from high resolution optical data and retrieves the precise absolute three-dimensional coordinates of the points from corrected TerraSAR-X timing measurements using the stereo SAR method [1]. Preliminary results for a test site in the city of Berlin acquired from TerraSAR-X high resolution spotlight mode are shown.

Identification

Control point

10.1109/igarss.2016.7729829

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Citations (6)

IEEE Transactions on Geoscience and Remote Sensing (2009)

Ulrich Balss Helko Breit Thomas Fritz

Synthetic aperture radar (SAR) image intensity is disturbed by additive system noise. During SAR focusing, pattern corrections that are adapted to the characteristics of the wanted signal, but not to the characteristics of the noise, influence the spatial distribution of the noise power. Particularly in the case of ScanSAR, a distinct residual noise pattern in low backscatter areas results. This necessitates a noise-adapted radiometric correction of the focused image for almost all applications except interferometry. In this paper, we thoroughly investigate this topic. Based on signal theoretical and stochastic considerations, we develop a radiometric correction scheme. Simulations and the application of the algorithm to TerraSAR-X datatakes support the theoretical results.

Radiometry

Backscatter (email)

10.1109/tgrs.2009.2035443

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Citations (20)

TerraSAR-X SAR Data Processing

Helko Breit Thomas Fritz Ulrich Balss Andreas Niedermeier Marie Lachaise

The TerraSAR-X Mission started operational provision of SAR image products to the scientific and commercial user community in January 2008. An essential prerequisite for the excellent quality of the SAR products was the successful execution of a comprehensive commissioning phase (CP) in 2007. Here, the complete SAR system which comprises instrument commanding, instrument SAR data acquisition as well as SAR processing has been characterized, calibrated and verified. Finally SAR image product verification ensured that the product performance parameters are within the specification. Besides the versatile high-resolution X-Band SAR instrument in space, featuring Stripmap, ScanSAR and Spotlight imaging modes in different polarizations, the TerraSAR Multi-Mode SAR Processor (TMSP) is the central part of the ground segment. Most instrument and SAR calibration parameters have been derived on basis of SAR image products generated by the TMSP. Therefore, already in the beginning of the CP the products had to be relatively radiometric calibrated and geometrical undistorted. An indispensable prerequisite for this was the imaging mode independent normalization of the processor gain as well as the incorporation of external information, i.e. a digital elevation model for the projection of the elevation gain antenna pattern onto the terrain surface and a model of the atmosphere accounting for additional propagation delays. During the CP the TMSP has been adjusted to the in-orbit characteristics of the SAR data and instrument internal calibration. This includes adaptations of calibration pulse processing to a modified internal calibration strategy, accounting for duty cycle dependent pulse energy and temperature dependent gain levels as well as a fine tuning of the signal and geometry based Doppler centroid estimation algorithm. Furthermore, the determination of the reference function for range focusing has been optimized. Finally, the spectral weighting of the SAR data has been adjusted in order to obtain well balanced impulse response function properties in terms of resolution, side lobe ratios and azimuth ambiguities. The presentation reviews the essential features of the TMSP, summarizes the TMSP adjustments and presents results of the SAR product verification.

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The Extended Timing Annotation Dataset for Sentinel-1—Product Description and First Evaluation Results

IEEE Transactions on Geoscience and Remote Sensing (2022)

Christoph Gisinger Ludivine Libert Petar Marinkovic Lukas Krieger Yngvar Larsen

This paper introduces the extended timing annotation dataset (ETAD) product for Sentinel-1 (S-1) which was developed in a joint effort of German Aerospace Center (DLR) and the European Space Agency (ESA). It allows to correct range and azimuth timing of S-1 images for geophysical effects as well as for inaccuracies in synthetic aperture radar (SAR) image focusing. In combination with the precise orbit solution, these effects determine the absolute geolocation accuracy of S-1 SAR images and the relative collocation accuracy of repeat pass image stacks. ETAD contains the gridded timing corrections for the tropospheric and ionospheric path delays, the tidal-based surface displacements, and the SAR processing effects, all of which are computed for each data take using standard models from geodesy and auxiliary atmospheric data. The ETAD product helps S-1 users to significantly improve the geolocation accuracy of the S-1 SAR products to better than 0.2 m and offers a potential solution for correcting large scale interferometric phase variations. The product layout and the product generation are described schematically. The paper also reports first results for different SAR techniques: first, the improvement in geolocation accuracy down to a few centimeters by verification of accurately surveyed corner reflector positions in the range-azimuth plane; second, the well-established offset-tracking technique, that is used for systematic ice velocity monitoring of ice sheets and glaciers, where ETAD can reduce velocity biases down to sub-centimetric values; and third, the correction of atmospheric phase contributions in wide-area interferograms used for national and European ground motion services. These early results proof the added value of the ETAD corrections and that the product design is well suited to be integrated into the processing flows of established SAR applications such as absolute ranging of targets, speckle/feature tracking and interferometry.

Geolocation

10.1109/tgrs.2022.3194216

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Citations (10)