Birgit Schättler

The TerraSAR-X Ground Segment

TerraSAR-X, the first national German remote-sensing satellite, was launched on June 15, 2007. It carries an X-band high-resolution synthetic aperture radar (SAR) instrument featuring imaging modes like StripMap, ScanSAR, and, particularly, SpotLight in a variety of different polarization modes. Primary mission goal is the provision of both science and commercial users with a variety of products from advanced SAR modes. The TerraSAR-X Ground Segment, which is provided by the German Aerospace Center (DLR), constitutes the central element for controlling and operating the TerraSAR-X satellite, for calibrating its SAR instrument, and for archiving the SAR data, as well as generating and distributing the basic data products. This paper depicts the ground-segment layout and describes its major elements. The ordering and product-generation workflow is presented. It introduces the applied prelaunch integration, testing, verification, and validation approach, a major key to the completion not only of the SAR technical-verification program but also the operational qualification of the ground segment itself within the commissioning phase.

TerraSAR-X SAR products and processing algorithms

TerraSAR-X is a German SAR satellite to be launched in 2006. The instrument is programmable in wide ranges and the dual polarized active phased array antenna is steerable in elevation and azimuth. Both features allow a number of imaging modes, among them stripmap, ScanSAR and spotlight. The later yields resolutions on the order of 1 meter. Geocoding and ortho-rectification capability is provided for all imaging modes. Additional experimental modes comprise an along track interferometric mode and a quad polarized mode. A wide product palette has been defined from the operational and experimental imaging modes that will be processed at and distributed by the German Aerospace Center DLR for commercial and scientific users. The employed SAR processing system is a new DLR development and will handle SAR data from the different acquisition modes (stripmap, ScanSAR, spotlight, multi-pol) and product variants (complex, detected, geocoded) in a unified way. This approach allows a coherent processor design and shall reduce the efforts for test, calibration and validation of the product tree. The paper summarizes the instrument operation modes, the applied processing algorithms and the product properties as they are relevant for the user. The geocoded product called Enhanced Ellipsoid Corrected will be described as well as the applied Digital Elevation Model Data Base (DEM-DB). Also details on phase preserving interferometric and polarimetric products are addressed.

SRTM/X-SAR: products and processing facility

The Shuttle Radar Topography Mission SRTM mapped the Earths surface in two frequencies - C-band and X-band. This paper presents the SRTM/X-SAR products, the processing and archiving facility as well as the procedures on how the products will be made available. The raw data volume stored online within the robot archive of DLRs Remote Sensing Data Center (DM) will be about four TBytes. The processing of this amount of data requires the use of high performance parallel computers scheduled and supervised by a new control and information system. The DEM production line is split into three subsystems the scanning and screening, the SAR as well as interferometric processing and finally the elevation derivation and mosaicking procedure. An online catalogue accessible via web browser provides all information required for a product selection.

RADARSAT ScanSAR interferometry

ScanSAR interferometry is an efficient technique for topographic mapping or surface change monitoring of large areas. The feasibility of ScanSAR interferometry has been demonstrated in theory and simulations before. The authors show the first ScanSAR interferogram from real RADARSAT data. In a first example, an interferogram derived from two ScanSAR data sets is presented. In a second example, an interferogram is formed from a ScanSAR a one strip-map data set. In this case, the azimuth synchronization problem involved in the acquisition of ScanSAR interferometric pairs is circumvented. Different interferometric ScanSAR algorithms are discussed.

A high precision workstation-based chirp scaling SAR processor

In order to meet the challenges of new spaceborne multi-mode SAR sensors and missions, a multi-sensor chirp scaling SAR processor is currently under development at the German Remote Sensing Data Center DFD. High precision data processing is ensured by floating point data representation, frequent processing parameter update as well as the underlying phase preserving chirp scaling algorithm enhanced to deal with arbitrary Doppler centroid variations over range. The availability of high performance general purpose computers enables the use of standard programming languages and hardware, even if a high throughput is required for operational applications. Multithreading software techniques lead to scalable processing systems running efficiently on different platforms ranging from single CPU workstations to multiprocessor systems. This paper describes the algorithms, the design and the implementation concept of this highly flexible SAR processor. Detailed image quality and throughput results based on simulated as well as real SAR data are presented.

The joint TerraSAR-X / TanDEM-X ground segment

This paper recalls the essential elements of the joint TerraSAR-X and TanDEM-X ground segment. It elaborates on some topics which are usually not in the primary focus from a pure SAR technical point of view, e.g. the flight formation. Both commissioning and early routine phase results from operating the joint TerraSAR-X and TanDEM-X ground segment are given.

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

TerraSAR-X, the first national German radar satellite, was launched in June 2007. It carries an X-band high-resolution synthetic aperture radar instrument featuring Stripmap, ScanSAR and, particularly, Spotlight imaging in a variety of different polarization modes. The mission completed its commissioning phase (CP) in December 2007, the provision of the SAR products for both the scientific and commercial user community was started in January 2008. One central TerraSAR-X element on ground is the pay-load ground segment PGS. From the beginning of the mission, PGS was nominally operated. About ten thousand data takes were already acquired and processed in 2007, not only for SAR verification and calibration purposes, but also for the operational ground segment validation. This paper provides the commissioning and early operational phase results from the SAR payload data processing perspective addressing data reception and SAR processing. Specifically the tuning and adjustment of the TerraSAR-X multi-mode SAR processor TMSP to meet the in-orbit data characteristics and to optimize the SAR focusing results is addressed. Relevant issues are the high-bandwidth chirp replica processing, side lobe suppression, Doppler frequency determination, processor normalization and phase-preservation.

TerraSAR-X Commissioning Phase Execution Summary

This paper provides an overview of the TerraSAR-X commissioning phase (CP). The overall CP planning and preparation is presented. The strategy for data-take (DT) command generation is discussed, and statistical reports summarize the acquired CP DTs. An overview summary on the main results in the different characterization and verification areas is provided together with synthetic aperture radar image examples.

The joint TerraSAR-X / TanDEM-X mission planning system

This paper recalls the essential system requirements and elements for the joint TerraSAR-X / TanDEM-X mission planning system. Its commissioning approach, tests and results are described in detail.

Doppler-Characteristics of the Ers-1 Yaw Steering Mode

Doppler centroid frequency and Dopple: FM rate are the most the Doppler variations in range [3,4]. The range migration can prominent parameters in SAR processing. In parncular, the be in particular prohibitive for a fast survey processor. The beneDoppler centroid depends on the antenna beam pointing and can fits of zero-Doppler line steelring for focussing on different terbe influenced by attitude control of the SAR platform. SAR Pro- rain hei hts, in particular for B X-SAR system, has been pointed cessing requirements are considerably relaxed, if the center out in h]. For squinted antenna angles a perfect focussing is beam points in the direction of the zero-Doppler line. This re- not longer possible, because of the dependence of the Doppler quires a continuous change in the attitude along the orbit and centroid on terrain height. Finally, squinted angles imply a skew is approximated in the yaw-steering operation mode of ERS-1. in the data and require then larger processing arrays, hence, deThe Doppler centroid characteristic predicted for this mode is creasing the system throughput. The yaw-steering mode of compared in this paper with the one estimated from ERS-1 SAR ERS-1 closely approximates the zero-Doppler line steering of signal data during nominal precision processing at the German the antenna and allows for the first time the evaluation of this Processing and Archiving Facility (D-PAF). Conclusions drawn mode for the ERS-1 platform. from this comparison may be helpful in the planning of future SAR missions.