The article proposes a novel approach for in-orbit satellite antenna pattern measurement by means of a dedicated small measurement satellite (MES) that flies in Double-Cross-Helix formation. For establishing and maintaining the quality of a satellite mission and its products, antenna pattern measurement while the satellite is in orbit is crucial. In remote sensing missions like synthetic aperture radar (SAR), the pattern is measured using calibration targets on the Earth’s surface. Such on-ground measurements are costly, time-consuming, and only offer 1-D azimuth or elevation patterns within constrained angular ranges. The novel approach provides a 2-D in-orbit measurement that covers the full angular range. The 2-D pattern is obtained from numerous central cuts resulting from small modifications of the MES’s orbit parameters that establish the Double-Cross-Helix formation. The measurement is performed in free space with a single free-flying MES. This avoids all distortions from atmosphere, ionosphere, ground clutter and multipath effects, ambiguities, and volume scattering. The approach is of great value for future satellite missions that are increasingly based on a huge number of electronically steered antenna beams and/or digital beamforming. The Dual-Cross-Helix approach provides faster, cheaper, and more accurate pattern measurements. The article discusses a high-level system concept of a feasible in-orbit pattern measurement of a SAR satellite similar to TerraSAR-X by means of a passive MES that is equipped with a reflecting sphere. Orbit simulations, measurement gain, and angular sampling accuracy analyses verify that the Double-Cross-Helix approach is feasible and advantageous for in-orbit antenna pattern measurement.

Spaceborne synthetic aperture radar (SAR) is an essential tool for Earth observation. The combination of multiple SAR images taken from different viewing angles allows forming accurate digital elevation models and high-resolution tomograms that unveil the three-dimensional structure of vegetation, ice, and dry soil. Whereas nowadays such images are mostly acquired sequentially, compromising product quality and hindering the monitoring of fast dynamics, multi-static SAR systems enable the simultaneous acquisition of all required data, paving the way for effective and powerful monitoring of our planet. One fundamental challenge is the conception of multi-static concepts that allow the generation of high-quality digital elevation models and tomograms from large sets of noisy and undersampled radar data acquired by clusters of smallsats with small antenna apertures. Swarms of drones, equipped with radars and localization systems, represent an affordable option to test multi-static concepts and acquire multi-static data with sub-hour temporal resolution.

The letter proposes a systematic derivation and description of dispersed synthetic aperture radar (SAR) for uniform intersatellite separation, points out some of its major challenges, that is, gapless sampling and power consumption, and provides solutions for them. Using a reference stripmap scenario, the improvements introduced by dispersed SAR using either fixed or alternating transmit satellites are discussed. It is shown that dispersed configurations allow for both a transmit power suited for small satellites and safe intersatellite separations.

This article reports the Phase A study results of the interferometric extension of the high-resolution wide-swath (HRWS) mission with three MirrorSAR satellites. According to the MirrorSAR concept, small, low-cost, transponder-like receive-only satellites without radar signal demodulation, digitization, memory storage, downlink, and synchronization are added to the planned German X-band HRWS mission. The MirrorSAR satellites fly a triple helix orbit in close formation around the HRWS orbit and span multiple single-pass interferometric baselines. A comprehensive system engineering and performance analysis is provided that includes orbit formation, MirrorLink, Doppler steering, antenna pattern and swath design, multi-static echo window timing, SAR performance, height performance, and coverage analysis. The overall interferometric system design analysis of Phase A is presented. The predicted performance of the global digital elevation model (DEM) is improved by one order of magnitude compared to presently available global DEM products such as the TanDEM-X DEM.

This article defines Doppler steering laws for different bi- and multistatic acquisition geometries for synthetic aperture radar (SAR). Central swath line (CSL) and transmit swath line (TSL) acquisition geometries are introduced. Bistatic zero Doppler steering (BZDS) is defined. Multistatic acquisitions are classified into dedicated and supplementary types. Numerical approaches for the calculation of yaw, pitch, and roll angles are described providing zero Doppler, constant Doppler, and/or full Tx-Rx beam footprint overlap. The appendix provides an approximated analytical approach to calculate yaw and pitch angles to achieve a desired swath line.

Synthetic aperture radar (SAR) interferometry is a well-established technique for producing high-resolution digital elevation models (DEMs) of the Earth’s surface and measuring displacements on different time scales. Observations of SAR interferograms, however, show that azimuth ambiguities can be coherently imaged and may lead to phase biases and coherence losses that significantly degrade the interferometric performance. Whereas imposing very low ambiguity levels may represent a severe design constraint for a spaceborne SAR system, a slight variation of the pulse repetition interval (PRI) is a new, simple, yet effective technique to decorrelate ambiguities, which in turn reduces the phase biases and coherence losses without substantially affecting the imaged swath width. An additional benefit of the PRI variation is that range ambiguities also become decorrelated. This paper addresses two cases: For the repeat-pass case, slightly different pulse repetition frequencies (PRFs) can be used for the two acquisitions and the minimum required PRF difference can be analytically derived resorting to the power spectral density of the ambiguous signals; For the single-pass case, a slight variation of the PRI during the common acquisition is an effective solution, in case an along-track baseline is present. In particular, a square wave PRI variation scheme outperforms sinusoidal or random ones. Finally, simulations using TanDEM-X data are presented to show the improvement in interferogram and DEM quality resulting from ambiguity decorrelation. This work is relevant for the design of future spaceborne interferometric SAR systems and for the enhanced exploitation of current ones.

This paper introduces the concept of a fractionated MirrorSAR which is based on a set of mutually separated transmitter and receiver satellites. As opposed to previously published bi- and multistatic SAR systems, the receiver satellites are considerably simplified, as their main functionality is reduced to a kind of microwave mirror (or space transponder) which routes the radar echoes towards the transmitter. The forwarded radar signals are then coherently demodulated within the transmitter by using the same oscillator that had been used for radar pulse generation. This avoids the necessity of a bidirectional phase synchronization link as currently employed in TanDEM-X. Since the needs for fully equipped radar receivers, on-board memory and downlink are also overcome, the weight and costs of the receiver satellites can be significantly reduced. This allows for a scaling of their number without cost explosion, thereby paving the way for novel applications like multi-baseline SAR interferometry and single-pass tomography. Several additional opportunities make the MirrorSAR concept even more attractive. First, the separation of the transmitter and receiver front-ends reduces not only RF losses by avoiding switches and circulators, but it may also lower the peak power in the transmitter satellite by employing a frequency-modulated continuous wave (FMCW) illumination. This simplifies the design of the high-power amplifier and increases its efficiency. Second, the opportunity for continuous radar data collection enables new modes for the imaging of ultra-wide swaths with very high resolution, thereby overcoming an inherent limitation of conventional monostatic SAR systems. Third, the joint availability of all receiver signals in a centralized node offers new opportunities for efficient data compression, as the multistatic radar signals from close satellite formations are characterized by a high degree of mutual redundancy. Fourth, the use of a sufficiently separated transmitter satellite can avoid the risk for mutual illumination, which challenges the design and operation of fully-active multistatic SAR systems. Further advantages arise from the scalability and reconfigurability, which support new redundancy concepts and pave at the same time the way to new modes like MIMO-SAR tomography.

This paper proposes the wrapped staring spotlight (WSS) SAR imaging mode, which is a new method to extend the azimuth steering capability for phased array SAR to achieve either an improved azimuth geometric or radiometric resolution. It investigates the utility of steering directions with main lobe gains that are smaller than that of the grating lobes and exposes how these directions can be exploited. Furthermore, two methods are proposed to reduce the speckle and the image noise at once, i.e., the Look-Normalized Pattern Correction and the Ω-weighting. Based on two example TerraSAR-X WSS acquisitions, the image performance of extended and point targets is discussed.

The paper investigates the possibility to enhance the TerraSAR-X (TSX) azimuth resolution by means of staring spotlight imaging in combination with an extended azimuth pattern steering. The current TSX spotlight modes are briefly reviewed, and the azimuth steering limitations are discussed. Based on a realistic TSX azimuth pattern simulation and performance estimation using a Kepler orbit and the WGS84 reference ellipsoid, the key performance parameters are estimated for an increasing azimuth pattern steering angle span. The azimuth ambiguity performance is identified to be the driving performance parameter. Experimental TSX staring spotlight high-resolution images are presented. They demonstrate and verify the envisaged performance estimation. The paper concludes with a concept for a high-resolution TSX staring spotlight mode that serves as baseline for the upcoming operational implementation.

This paper addresses several important aspects that need to be considered for the processing of spaceborne synthetic aperture radar (SAR) data with resolutions in the decimeter range. In particular, it will be shown how the motion of the satellite during the transmission/reception of the chirp signal and the effect of the troposphere deteriorate the impulse response function if not properly considered. Further aspects that have been investigated include the curved orbit, the array pattern for electronically steered antennas, and several considerations within the processing itself. For each aspect, a solution is proposed, and the complete focusing methodology is expounded and validated using simulated point targets and staring spotlight data acquired by TerraSAR-X with 16-cm azimuth resolution and 300-MHz range bandwidth.

This paper introduces the bidirectional synthetic aperture radar (BiDi SAR) imaging mode, i.e., the simultaneous imaging of two directions by one antenna into one receiving channel, and presents short-term time series of images and interferograms acquired by the TerraSAR-X and TanDEM-X satellites. A comparison to alternative approaches for the acquisition of short-term time series is provided. The BiDi acquisition geometry is defined, and a TerraSAR-X BiDi antenna pattern is analyzed. BiDi raw data are simulated, sampled with different pulse repetition frequency values, and compared with real BiDi raw data. The spectral separation of simultaneously acquired forward- and backward-looking images is explained. This paper presents the image results of BiDi acquisitions with TerraSAR-X and TanDEM-X satellites flying with 20-km along-track separation. This pursuit configuration allowed for the acquisition of up to six short-term repeated images and up to three interferograms in a single pass. An overview of potential applications for the new BiDi SAR imaging mode concludes this paper.

Two Block Adaptive Quantization (BAQ) algorithms considered for implementation on-board Sentinel-1, the Entropy Constrained BAQ (ECBAQ) and the Flexible Dynamic BAQ (FDBAQ) are investigated with real data acquired by TerraSAR-X. The two algorithms are compared with respect to the resulting signal-to-quantization-noise ratio (SQNR) and the compression rate. The results confirm the improved performance of FDBAQ to be expected for Sentinel-1 compared to the more conventional ECBAQ.

This paper presents an initial analysis of the possibilities for velocity and acceleration measurement with the Bi-Directional SAR imaging mode (BiDi). It comprises single satellite single path acquisitions as well as a constellation of two satellites. The translational velocity components into azimuth and range directions are simulated. A BiDi approach for measuring the azimuth velocity from one satellite with one receiving channel is proposed. Image examples acquired with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites show velocity and acceleration effects on ships and the proposed BiDi velocity approach is verified. Interferometric fringes were observed on anchoring ships. A first approach into the understanding of rotational effects was achieved by simulation of rotational fringes.

This paper presents the outcome of a staring spotlight experiment with TerraSAR-X for considerably enhanced azimuth resolution. The commanding is discussed in terms of calculation of the azimuth steering angle. The performance estimation results are given for TerraSAR-X parameters and a steering angle range from -2.2° to +2.2°. The first TerraSAR-X staring spotlight images are presented.

This paper addresses several innovative steps needed in the chirp scaling and extended chirp scaling (ECS) algorithms in order to process staring Spotlight TerraSAR-X (TSX) images with 21 cm azimuth resolution and 300 MHz range bandwidth. The aspects that need of special consideration are the 2D phase truncation in frequency domain of ECS, the element pattern of the antenna array, the curved orbit, the stop-and-go approximation, and the troposphere. All these aspects are expounded in detail and a solution is given for each of them. The suggested corrections are applied at raw data level, hence easing the integration within the existing TSX processor. Real data acquired by TSX in the experimental staring Spotlight mode are used to validate the proposed methodology.

This letter presents an investigation on scalloping correction in the Terrain Observation by Progressive Scan (TOPS) imaging mode for synthetic aperture radar systems with electronically steered phased array antennas. A theoretical simulation of the scalloping is performed, and two correction methods are introduced. The simulation is based on a general cardinal sine (sinc) antenna model as well as on the TerraSAR-X (TSX) antenna model. Real TSX data acquired over rainforest are used for demonstration and verification of the scalloping simulation and correction. Furthermore, a calibration approach, taking into account the special TOPS imaging mode properties, is introduced.

Global backscatter data can be used for accurate synthetic aperture radar (SAR) performance estimation and optimizing instrument settings for SAR systems, e.g. the TerraSAR-X mission (TSM) and the TanDEM-X mission (TDM). The goal of this work is the generation of X-band backscatter maps by mosaicking images acquired by the TSM. An algorithm that allows the estimation of the on-ground backscatter, for any required polarization and incidence angle from the available data, is implemented. In this paper, the backscatter map generation algorithm is presented, together with the first results, obtained from the TSX-1 data. The validity of the interpolation models is also discussed, as they will form the basis for a future global statistical analysis and modeling of backscatter behavior in X-band SAR data.

The goal of this work is the generation of an X-Band backscatter map by assembling images acquired by the TerraSAR-X mission. Global backscatter data is required for accurate performance estimation and instrument commanding inside the TerraSAR-X and TanDEM-X missions. Moreover, many scientific applications can be based on the analysis of backscatter behavior and evolution. The complete ground coverage will be achievable with TanDEM-X mission data. An interpolator, that allows the estimation of the backscatter for any required polarization and incidence angle from the available data, has been implemented. In this paper, the backscatter map generation algorithm will be presented, together with the first obtained results, generated using TerraSAR-X data. Moreover, the validity of the interpolation models will also be discussed, presenting the preliminary results of a statistical analysis of backscatter from TerraSAR-X data.

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.

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.

This paper presents results from the synthetic aperture radar (SAR) system performance characterization, optimization, and verification as carried out during the TerraSAR-X commissioning phase. Starting from the acquisition geometry and instrument performance, fundamental acquisition parameters such as elevation beam definition, range timing, receiving gain, and block adaptive quantization setting are presented. The verification of the key performance parameters—ambiguities, impulse-response function, noise, and radiometric resolution—is discussed. ScanSAR and Spotlight particularities are described.

This paper presents an efficient phase preserving processor for the focusing of data acquired in sliding spotlight and Terrain Observation by Progressive Scans (TOPS) imaging modes. They share in common a linear variation of the Doppler centroid along the azimuth dimension, which is due to a steering of the antenna (either mechanically or electronically) throughout the data take. Existing approaches for the azimuth processing can become inefficient due to the additional processing to overcome the folding in the focused domain. In this paper, a new azimuth scaling approach is presented to perform the azimuth processing, whose kernel is exactly the same for sliding spotlight and TOPS modes. The possibility to use the proposed approach to process data acquired in the ScanSAR mode, as well as a discussion concerning staring spotlight, is also included. Simulations with point targets and real data acquired by TerraSAR-X in sliding spotlight and TOPS modes are used to validate the developed algorithm.

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.

This paper presents an efficient phase preserving processor for the focusing of data acquired in sliding spotlight, TOPS (Terrain Observation by Progressive Scans) and ScanSAR imaging modes. They share in common a linear variation of the Doppler centroid along the azimuth dimension, which is due to a steering of the antenna (either mechanically or electronically) throughout the data take for the first two modes, and due to the burst mode in the ScanSAR case. Existing approaches for the azimuth processing can become inefficient due to the additional processing to overcome the folding in the focused domain. In this paper an azimuth scaling approach is presented to perform the azimuth processing, whose kernel is the same for all three modes. Data acquired by TerraSAR-X in sliding spotlight, TOPS and ScanSAR modes are used to validate the developed algorithm.

The paper presents selected results from the TerraSAR-X Commissioning Phase from instrument performance, SAR system performance and command generation.

The paper summarizes the results of the TerraSAR-X commissioning phase. The overall schedule and the planning tool are presented. The strategy for data take (DT) command generation and a statistic about all acquired data takes are discussed. An overview about the characterization/verification results is provided.

Data compression is crucial for modern synthetic aperture radar systems where high resolution or large coverage may result in huge amounts of raw data. Modern satellite systems, such as TerraSAR-X, give complete flexibility in choosing between various compression levels. This, however, results in additional effort to decide on the suitable compression level used, which may depend on the operation mode, polarization, scene backscatter, etc. The paper describes the approach used in the case of TerraSAR-X and shows the result of analyzing the data acquired during the commissioning phase. The methology is considered novel in the sense that it combines SAR measured data analysis with theoretical, i.e. model based simulations, results and later combines theory and measured data to extract optimum compression levels.

The paper reports about investigations on the implementation of the recently proposed TOPSAR acquisition mode with TerraSAR-X. Differently from ScanSAR,TOPSAR mode allows a wide swath coverage with nearly uniform signal to noise ratio (SNR), therefore avoiding scalloping and azimuth dependent SNR. To achieve this goal the antenna beam is steered within the different swaths in the along-track direction. TerraSAR-X can electronically steer the azimuth beam; however, angle quantization is introduced because of the limited number of available azimuth beams per data take. The effects of the TerraSAR-X angle quantization of the antenna steering are analyzed resulting in a negligible distortion. The maximum azimuth steering angle of TerraSAR-X allows the implementation of TOPSAR with the same coverage and resolution as the nominal TerraSAR-X ScanSAR mode, four range subswaths with 16 m azimuth resolution and a total swath of 100 km. Finally,TerraSAR-X TOPSAR interferometry capability and the possibility of using an inverse TOPSAR configuration are discussed.

The paper discusses the areas covered by the TerraSAR-X Calibration/Verification-Plan. By means of a commissioning phase planning tool the data take requests required for characterization, calibration and verification are sequentially arranged. The status of the individual data takes is tracked from request planning to the final image analysis. All data take requests and results are supervised and summarized in a so-called verification matrix. In the end the paper gives an overview about the commissioning phase schedule and the repeat cycle based planning.

This paper presents an efficient phase preserving processor for TOPS (Terrain Observation by Progressive Scans) imaging mode. TOPS has been proposed as a new wide swath imaging mode, which solves the problems of scalloping and azimuth-varying ambiguities introduced by the conventional ScanSAR mode by means of steering the antenna along the azimuth direction. An algorithm based on ECS (Extended Chirp Scaling) is proposed, which uses sub-apertures and a new azimuth scaling step. The proposed solution is also efficient in the sense that it allows selecting the final azimuth image spacing by means of azimuth scaling, hence easing the forthcoming mosaicking of the different sub swaths. Simulations with point targets are used to validate the processor.

TerraSAR-X is a German satellite to be launched towards end of the year 2006. The SAR instrument built by EADS/Astrium has a multipolarized active phased array antenna and is programmable in wide ranges. This allows to operate imaging modes such as e.g. stripmap, spotlight, ScanSAR and dual-polarization modes. By further dividing the antenna in halves with different position or different polarization, experimental modes for ground moving target detection (GMT) or Quad-Polarization are possible. As a consequence of the various sensor capabilities the tree of SAR products offered by the DLR Ground Segment contains many different variants of polarization, resolution and scene size. Even more product variants are caused by different processing parameters selectable by the user. Some product performance parameters, such as the radiometric accuracy as a function of geometric resolution or the image resolution as a function of incidence angle depend on both, sensor settings (PRF, pulse duration) and on processing parameters (bandwidth, weighting, multi-looking). The processing parameters for the products have been designed by DLR in a way so that valuable products with maximum information content are offered to the user. In order to generate the specified products, the TerraSAR Multi Mode SAR Processor TMSP has been designed by DLR. This processor will be operated at the DLR payload ground segment in Neustrelitz for commercial and scientific customers. The processor will also be operated at additional direct access partner stations of Infoterra GmbH, who will serve private and public customers.

This letter presents a new method, called total Zero Doppler steering, to perform yaw and pitch steering for spaceborne synthetic aperture radar (SAR) systems. The new method reduces the Doppler centroid to theoretically 0 Hz, independent of the range position of interest. Residual errors are only due to pointing inaccuracy or due to approximations in the implementation of the total zero Doppler steering law. This letter compares the new method with currently applied methods. The attitude angles and the residual Doppler centroid frequencies are calculated and depicted exemplarily for the parameters of TerraSAR-X, for which the new method will be implemented and used. The new method provides a number of advantages. The low residual Doppler centroid and the reduced variation of the Doppler centroid over range allow a more accurate Doppler centroid estimation. Due to the low residual Doppler centroid, the synthetic aperture radar (SAR) processing can be alleviated, since the range cell migration is reduced and the Doppler frequencies are low. This facilitates the use of very efficient processing algorithms, which are based on approximations whose quality is better for low Doppler frequencies. The new method will furthermore optimize the overlap of the azimuth spectra of SAR image pairs for cross-track interferometry. Low Doppler centroids will also reduce the impact of coregistration errors on the interferometric phase. Furthermore, scalloping corrections in the ScanSAR processing are alleviated due to the low variation of the Doppler centroid over range.

This paper describes a new method to perform zero Doppler steering, namely Total Zero Doppler Steering. It is developed for spaceborne synthetic aperture radar (SAR) systems. This new method combines the yaw-steering with an additional pitch-steering, resulting in a Doppler centroid of theoretically zero Hertz over the whole desired range of incidence angles for the whole orbit and simultaneously for left and right looking geometry.

This paper presents a radiometric resolution optimization strategy which can be used in new generation of Synthetic Aperture Radar (SAR) systems. An expression, which allows optimization depending on application, has been developed for this purpose. In particular, special effort has been made for improving the radiometric resolution keeping the geometric resolution constant. Optimization examples have been carried out with realistic parameters taken from TerraSAR-X. The objective is to provide an effective and realistic way to tradeoff the instrument parameters for optimal exploitation of SAR images. Furthermore, a precise SNR formulation has been derived including processing gain and noise distribution

This paper evaluates the Spotlight processing accuracy for TerraSAR-X. It describes the developed Spotlight raw data simulator. Approximations in the Sliding Spotlight processing are calculated and verified by using this simulator. Based on a worst case scenario, raw data were simulated and processed with an Extended Chirp Scaling algorithm for Sliding Spotlight. The simulation results demonstrate the applicability of the processing algorithm for TerraSAR-X.

A major driver for the cost of a SAR satellite is the size of the antenna, which largely determines the dimensions of the payload, and, hence, indirectly of the whole satellite. As part of the SAFARI study to develop strategies for future space-borne SAR systems, techniques were investigated for suppressing ambiguities during processing, in order to relax the requirements on the antenna. The techniques are also valid for airborne SAR systems. The paper summarises the methods and discusses the impact on sensor design and the applications.

Abstract — This paper describes the sliding spotlight algorithm and the processing strategy to be applied for TerraSAR-X. The steering spotlight geometry is analysed. Analysis of scene size and resolution demonstrates the particularities of this mode. The Doppler frequencies for individual targets and for a whole sliding spotlight scene are analyzed and the result shows the applicabil-ity of azimuth subaperture processing to sliding spotlight data. A description of the Extended Chirp Scaling Algorithm for sliding spotlight is presented.

This Paper provides a demonstrative derivation of the effect of up and down chirp modulation on point and extended target signals. Analysis has been performed with respect to signal amplitude, signal extension, modulation rate and phase behavior. The suppression of "point target" range ambiguities is investigated for the a possible TerraSAR-X parameter setting. Extended targets have been simulated and filtered. A Range-Ambiguity Simulator is under development which is based on airborne X-band data from the Experimental SAR (E-SAR) of DLR. The simulator concept is presented.

This Paper describes the newly introduced Dual Re- ceive Antenna Mode (DRA) of the TerraSAR-X instrument. It explains the principle of forming two receiving antennas and deals with the already identified new applications and experi- ments enabled by this new mode, e.g. along track interferometry, geometric resolution enhancement and full polarimetric mode.

The results of an interferometric performance analysis for spaceborne parasitic SAR configurations are presented. The analysis includes errors due to limited SNR, block adaptive quantization, range and azimuth ambiguities, and geometric decorrelation for both flat surfaces and random volumes. Relative height accuracies for three spaceborne configurations with PALSAR, ASAR and TerraSAR-X as illuminators are derived and compared.

This paper presents a new processing algorithm for spotlight SAR data processing. The algorithm performs the range cell migration correction for non-chirped raw data without interpolation by using a novel frequency scaling operation. The azimuth processing is based on a spectral analysis approach which is made highly accurate by azimuth scaling. In almost all processing stages, a subaperture approach is introduced for efficient azimuth processing. In this paper, the complete derivation of the algorithm is presented. A very useful formulation for non-chirped SAR signals in the range Doppler domain is also proposed where the residual video phase is expressed by a chirp convolution. The algorithm performance is shown by several simulations. A spotlight image, which has been extracted from stripmap raw data of the experimental SAR system of DLR, shows the validity of the frequency scaling algorithm.

Presents a generalized formulation of the extended chirp scaling (ECS) approach for high precision processing of air- and spaceborne SAR data. Based on the original chirp scaling function, the ECS algorithm incorporates a new azimuth scaling function and a subaperture approach, which allow an effective phase-preserving processing of ScanSAR data without interpolation for azimuth geometric correction. The azimuth scaling can also be used for automatic azimuth coregistration of interferometric image pairs which are acquired with different sampling distances. Additionally, a novel range scaling formulation is proposed for automatic range coregistration of interferometric image pairs or for improved robustness for the processing of highly squinted data. Several simulation and processing results of air- and spaceborne SAR data are presented to demonstrate the validity of the proposed algorithms.