Multistatic SAR Imaging: First Results of a Four Phase Center Experiment with TerraSAR-X and TanDEM-X

Multichannel synthetic aperture radar (SAR) imaging offers the possibility to overcome the pulse repetition frequency (PRF) constraints inherent to single-channel SAR systems. The multichannel approach enables the acquisition of wide swathes with high azimuth resolution. Using a constellation or swarm of small satellites, a cost efficient, faulttolerant system can be envisaged. This paper describes the first results of a multistatic four phase center experiment conducted with TerraSAR-X and TanDEM-X. The experiment is intended to increase the know-how and demonstrate the capabilities for the design of future SAR systems. Key challenges are addressed, the experimental acquisition is described and an evaluation approach is presented. Finally, first results focusing on the azimuth ambiguity performance are shown

Multistatic SAR Imaging: Comparison of Simulation Results and Experimental Data

Synthetic aperture radar (SAR) systems in a multistatic configuration are a promising candidate for future Earth observation and reconnaissance radar systems. They overcome the sampling constraints inherent to single-channel SAR systems. Thus, a multistatic SAR system enables the acquisition of high-resolution images while maintaining wide-swath coverage. Employing several small satellites instead of a single large one, a cost-efficient system with graceful degradation characteristics can be envisaged. Additionally, such a constellation or swarm of sensors offers interferometric and tomographic capabilities, which a single-satellite system is not able to provide. This paper shows results of multistatic experiments obtained with TerraSAR-X and TanDEM-X and compares these results with theoretical simulations. The key parameters analyzed are the Doppler spectrum and the azimuth ambiguity suppression

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 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 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 dual receive antenna 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 ground moving target indication capability of the TerraSAR-X dual receive antenna mode are given

Oil spill and ship detection using high resolution polarimetric X-band SAR data

Among illegal human activities, marine pollution and target detection are the key concern of Maritime Security and Safety. This thesis deals with oil spill and ship detection using high resolution X-band polarimetric SAR (PolSAR). Polarimetry aims at analysing the polarization state of a wave field, in order to obtain physical information from the observed object. In this dissertation PolSAR techniques are suggested as improvement of the current State-of-the-Art of SAR marine pollution and target detection, by examining in depth Near Real Time suitability

A Waveform-Encoded SAR Implementation Using a Limited Number of Cyclically Shifted Chirps

Synthetic aperture radar (SAR) provides high-resolution images of the Earth’s surfaceirrespective of sunlight and weather conditions. In conventional spaceborne SAR, nadir echoescaused by the pulsed operation of SAR may significantly affect the SAR image quality. Therefore,the pulse repetition frequency (PRF) is constrained within the SAR system design to avoid theappearance of nadir echoes in the SAR image. As an alternative, the waveform-encoded SAR conceptusing a pulse-to-pulse variation of the transmitted waveform and dual-focus postprocessing canbe exploited for nadir echo removal and to alleviate the PRF constraints. In particular, cyclicallyshifted chirps have been proposed as a possible waveform variation scheme. However, a largenumber of distinct waveforms is required to enable the simple implementation of the concept.This work proposes a technique based on the Eulerian circuit for generating a waveform sequencestarting from a reduced number of distinct cyclically shifted chirps that can be effectively exploitedfor waveform-encoded SAR. The nadir echo suppression performance of the proposed scheme isanalyzed through simulations using real TerraSAR-X data and a realistic nadir echo model thatshows how the number of distinct waveforms and therefore the system complexity can be reducedwithout significant performance loss. These developments reduce the calibration burden and makethe concept viable for implementation in future SAR systems

Study of the speckle noise effects over the eigen decomposition of polarimetric SAR data: a review

This paper is focused on considering the effects of speckle noise on the eigen decomposition of the co- herency matrix. Based on a perturbation analysis of the matrix, it is possible to obtain an analytical expression for the mean value of the eigenvalues and the eigenvectors, as well as for the Entropy, the Anisotroopy and the dif- ferent a angles. The analytical expressions are compared against simulated polarimetric SAR data, demonstrating the correctness of the different expressions.Peer ReviewedPostprint (published version

TerraSAR-X Dual Receive Antenna Mode, Calibration and GMTI Performance Assessment

Synthetic aperture radar with multiple channels separated in along-track direction allows for GMTI such as detection of road traffic. With TerraSAR-X two receive channels separated in along-track direction can either be realized through switching between the fore and aft antenna halves on a pulse to pulse basis, or with the dual receive antenna (DRA) mode. While the switching in the single channel switched aperture mode is implemented by alternately applying attenuation to the fore and aft antenna halves, in the DRA mode the signals of the fore and aft antenna halves are combined by a hybrid coupler generating the sum and difference channel data. By use of the redundant receiver unit both channels are sampled separately. Fore and aft channel signals have to be reconstructed in the signal processing step. In this paper the fore and aft channel reconstruction in the TerraSAR-X dual receive antenna mode is described. Then, the residual imbalances are modeled into the transfer function in order to analyze the quality of signal reconstruction and draw conclusions on the ground moving target indication (GMTI) performance of this two-channel mode. The theoretical results derived are validated with experimental data and GMTI results are shown

TerraSAR-X Dual Receive Antenna Mode: Experimental Data Results on Azimuth Ambiguity Suppression and GMTI

The German synthetic aperture radar (SAR) satellite TerraSAR-X provides the option to split the antenna in along-track direction and sample two physical channels separately. In the so-called dual receive antenna (DRA) mode the redundant receiver unit is used as the second channel and the fore and aft channel data are combined by use of a hybrid junction. Therefore, the fore and aft channel data have to be reconstructed in the processing. In this paper first results on the ground moving target indication (GMTI) capability of the TerraSAR-X DRA mode employing a channel reconstruction procedure based on internal calibration pulses and calibration beams are shown. Since usually with GMTI applications also a SAR image of the scene is required, the system configuration for optimum SAR imaging versus optimum GMTI is discussed

Remote Sensing and Geosciences for Archaeology

This book collects more than 20 papers, written by renowned experts and scientists from across the globe, that showcase the state-of-the-art and forefront research in archaeological remote sensing and the use of geoscientific techniques to investigate archaeological records and cultural heritage. Very high resolution satellite images from optical and radar space-borne sensors, airborne multi-spectral images, ground penetrating radar, terrestrial laser scanning, 3D modelling, Geographyc Information Systems (GIS) are among the techniques used in the archaeological studies published in this book. The reader can learn how to use these instruments and sensors, also in combination, to investigate cultural landscapes, discover new sites, reconstruct paleo-landscapes, augment the knowledge of monuments, and assess the condition of heritage at risk. Case studies scattered across Europe, Asia and America are presented: from the World UNESCO World Heritage Site of Lines and Geoglyphs of Nasca and Palpa to heritage under threat in the Middle East and North Africa, from coastal heritage in the intertidal flats of the German North Sea to Early and Neolithic settlements in Thessaly. Beginners will learn robust research methodologies and take inspiration; mature scholars will for sure derive inputs for new research and applications