Ulrich Steinbrecher

TOPS Imaging With TerraSAR-X: Mode Design and Performance Analysis

This paper reports about the performed investigations for the implementation of the wide-swath TOPS (Terrain Observation by Progressive Scan) imaging mode with TerraSAR-X (TSX). The TOPS mode overcomes the limitations imposed by the ScanSAR mode by steering the antenna along track during the acquisition of a burst. In this way, all targets are illuminated with the complete azimuth antenna pattern, and, thus, scalloping is circumvented, and an azimuth dependence of signal-to-noise ratio and distributed target ambiguity ratio (DTAR) is avoided. However, the use of electronically steered antennas leads to a quantization of the steering law and a nonideal pattern for squinted angles (grating lobes and main lobe reduction). The former provokes spurious peaks, while the latter introduces slight scalloping and DTAR deterioration. These effects are analyzed and quantified for TSX, and a TOPS system design approach is presented. Next, the requirements concerning interferometry are investigated. Finally, several results are shown with the TSX data, including a comparison between the TOPS and the ScanSAR modes and the reporting of the first TOPS interferometric results.

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

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.

X-SAR interferometry: first results

Repeat-pass interferometry data were acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry at four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model in ground range geometry has been derived. The limitations of the X-SAR interferometry are discussed. >

First Bistatic Spaceborne SAR Experiments With TanDEM-X

TanDEM-X (TerraSAR-X Add-on for Digital Elevation Measurements) is a high-resolution interferometric mission with the main goal of providing a global and unprecedentedly accurate digital elevation model of the Earth surface by means of single-pass X-band synthetic aperture radar (SAR) interferometry. Despite its usual quasi-monostatic configuration, TanDEM-X is the first genuinely bistatic SAR system in space. During its monostatic commissioning phase, the system has been mainly operated in pursuit monostatic mode. However, some pioneering bistatic SAR experiments with both satellites commanded in nonnominal modes have been conducted with the main purpose of validating the performance of both space and ground segments in very demanding scenarios. In particular, this letter reports about the first bistatic acquisition and the first single-pass interferometric (mono-/bistatic) acquisition with TanDEM-X, addressing their innovative aspects and focusing on the analysis of the experimental results. Even in the absence of essential synchronization and calibration information, bistatic images and interferograms with similar quality to pursuit monostatic have been obtained.

Fore and Aft Channel Reconstruction in the TerraSAR-X Dual Receive Antenna Mode

The TerraSAR-X satellite is a high-resolution synthetic aperture radar (SAR) system launched in June 2007 which provides the option to split the antenna in along-track direction and sample two physical channels separately. Modern SARs are equipped with active phased array antennas and multiple channels. In order to keep costs low, TerraSAR-X uses the redundant receiver unit for the second channel such that fore and aft channel signals are combined by a hybrid coupler to form sum and difference channel data. The dual receive antenna (DRA) mode can either be used to acquire along-track interferometric data or to acquire signals with different polarizations at the same time (Quad-Pol). Fore and aft channel reconstruction is necessary if ground moving target indication (GMTI) algorithms such as the displaced phase center antenna technique or along-track interferometry shall be applied, and in order to separate the horizontally and vertically polarized received signal components. The proposed approach uses internal calibration pulses from different calibration beams in order to estimate and compensate the hardware impact. The theoretical framework together with the results from the experimental data evaluation for the fore and aft channel reconstruction of the TerraSAR-X DRA mode are presented. The impact of the receive hardware transformation matrix estimation accuracy on errors in the reconstructed fore and aft channel image data is studied, and first examples on the GMTI capability of the TerraSAR-X DRA mode are given.

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.

Algorithms for X-SAR processing

The German/Italian X-SAR is an X-band SAR to be flown together with the SIR-C instrument on the Shuttle Radar Lab missions in April and December 1994. The paper describes the algorithms used in the X-SAR processor at DLR.<<ETX>>

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 Instrument Operations Rooted in the System Engineering and Calibration Project

This paper presents the TerraSAR-X instrument operations embedded into the Instrument Operations and Calibration Segment. Special focus is on the data-take (DT) command generation. The command generation for standard DTs is discussed, and the nonnominal DT commanding is described for several examples which demonstrate the flexibility of both the TerraSAR-X instrument and the instrument operations system on-ground.