Andreas R. Brenner

Bistatic SAR Processing and Experiments

Bistatic synthetic aperture radar (SAR) uses a separated transmitter and receiver flying on different platforms to achieve benefits like exploitation of additional information contained in the bistatic reflectivity of targets, reduced vulnerability for military applications, forward-looking SAR imaging, or increased radar cross section. Besides technical problems such as synchronization of the oscillators, involved adjustment of transmit pulse versus receive gate timing, antenna pointing, flight coordination, and motion compensation, the development of a bistatic focusing algorithm is still in progress and not sufficiently solved. As a step to a numerically efficient processor, this paper presents a bistatic range migration algorithm for the translationally invariant case, where transmitter and receiver have equal velocity vectors. In this paper, the algorithm was successfully applied to simulated and real bistatic data. The real bistatic data have been acquired with the Forschungsgesellschaft fur Angewandte Naturwissenschaften (FGAN)s X-band SAR systems, namely the Airborne Experimental Radar II and the Phased Array Multifunctional Imaging Radar, in October 2003

Bistatic SAR Experiments With PAMIR and TerraSAR-X—Setup, Processing, and Image Results

The spatial separation of the transmitter and the receiver in bistatic synthetic aperture radar (SAR) enables a variety of data acquisition geometries to achieve benefits like the increased information content of bistatic SAR data. In the case of hybrid bistatic SAR constellations where the transmitter is spaceborne and the receiver is onboard an aircraft, one has to deal with a huge discrepancy between platform velocities. This paper presents bistatic spaceborne/airborne SAR experiments, where the radar satellite TerraSAR-X is used as a transmitter and the airborne SAR sensor Phased Array Multifunctional Imaging Radar (PAMIR) of the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) is used as a receiver. Both sensors are equipped with phased-array antennas, which offer the possibility of beam steering and could be used for the first time for the “double sliding spotlight mode.” In this mode, the space- and airborne sensors operate with different sliding factors (ratio between footprint and platform velocity). The performance of two different experiments is analyzed, and the novel double sliding spotlight mode is presented. This paper describes the experimental setups, the synchronization system, and the data acquisition. The image results were processed by a modified backprojection algorithm and a frequency-domain algorithm. The analysis of the final bistatic images comprises the spatial resolution and the scattering behavior of selected objects. Parts of the bistatic SAR images are compared with the corresponding monostatic images of PAMIR and TerraSAR-X. It will be shown that hybrid bistatic SAR is a worthwhile and helpful addition to current monostatic SAR.

Wide-Area Traffic Monitoring With the SAR/GMTI System PAMIR

This paper presents a wide area traffic monitoring experiment under real conditions, using the scan-MTI mode of the airborne radar sensor PAMIR. This flexible GMTI (Ground Moving Target Indication) mode was designed in order to rapidly monitor wide areas for moving targets. The scan operation enables the detection of targets from different aspect angles with a high revisit rate. The parameters (e.g., radial velocity, signal-to-noise ratio, and positioning accuracy) of the detected vehicles are investigated and compared to the expected theoretical GMTI performance. It will be shown that the scan-MTI mode is particularly adapted to perform an efficient wide-area traffic monitoring.

New aspects of bistatic SAR: processing and experiments

The interest in bistatic synthetic aperture radar, using separated transmitter and receiver flying on different platforms, has been increasing rapidly over the last years. The reason for this is specific advantages, like the reduced vulnerability in military systems, forward looking SAR imaging, additional information about the target, or increased RCS. Nevertheless, besides technical problems - like the synchronisation of the oscillators, the involved adjustment of transmit pulse versus receive gate timing, antenna pointing, flight coordination, double trajectory measurement and motion compensation - the processing of bistatic radar data is still not sufficiently solved. Some of the possibilities and problems discussed. The second part of This work deals with a bistatic experiment performed in November 2003: two SAR systems of FGAN have been flown on two different airplanes, the AER-II system has been used as a transmitter and the PAMIR system as a receiver. Different spatially invariant flight geometries have been tested. High resolution bistatic SAR images were generated successfully.

Radar imaging of urban areas by means of very high resolution SAR and interferometric SAR

In remote-sensing applications, the monitoring of urban areas by means of synthetic aperture radar (SAR) sensors has grown into a valuable and indispensable tool. Although SAR imaging with a spatial resolution down to 1 m is widespread, a resolution as fine as 10 cm and below is offered only by very few SAR sensors worldwide. In this paper, the potential of very high-resolution radar imaging of urban areas by means of SAR and interferometric imaging will be demonstrated and discussed. Results of urban SAR imaging down to subdecimeter resolution will be shown. Even though the immanent layover situation in urban areas is an obstacle to simple image understanding, a remedy can be found by using interferometric SAR imaging. Interferometric results based on very high-resolution SAR images acquired over urban areas, partially with a severe layover situation, will be presented. The corresponding data was acquired with the phased array multifunctional imaging radar (PAMIR), the X-band demonstrator of the Research Institute for High Frequency Physics and Radar Techniques (FHR), Forschungsgesellschaft fur Angewandte Naturwissenschaften (FGAN), Wachtberg, Germany. It can be stated that high-resolution interferometric SAR will be an important basis for upcoming radar-based urban analysis.

Bistatic Forward-Looking SAR: Results of a Spaceborne–Airborne Experiment

Forward-looking radar imaging continues to gain in significance due to a variety of convenient applications, like landing assistance for aircraft in poor visibility conditions. Synthetic aperture radar (SAR) techniques are typically used to achieve a high azimuth resolution, but conventional monostatic SAR is not applicable in forward direction because of azimuth ambiguities and poor Doppler resolution. To improve the Doppler resolution and to avoid azimuth ambiguities, bistatic SAR configurations can be used to obtain high-resolution radar images. This is demonstrated for the first time in a spaceborne-airborne SAR experiment by using TerraSAR-X as the illuminator and the Phased Array Multifunctional Imaging Radar as the receiver. For convenience, the receivers SAR antenna was mounted on the aircrafts loading ramp and looked backward. Due to identical image properties and the same challenges for forward- and backward-looking sensors, this configuration also demonstrates the feasibility of forward-looking bistatic SAR. This letter describes the experimental setup, analyzes the performance, and presents the imaging results.

Bistatic SAR processing using an Omega-K type algorithm

Bistatic SAR uses separated transmitter and receiver flying on different platforms to achieve benefits like exploitation of additional information contained in the bistatic reflectivity of targets, reduced vulnerability in military systems, forward looking SAR imaging [1] or increased RCS. Besides of technical problems, like the synchronization of the oscillators, the involved adjustment of transmit pulse versus receive gate timing, antenna pointing, flight coordination and motion compensation, the development of bistatic focusing algorithm is still in progress and not sufficiently solved. As a step to a numerically efficient processor, an omega-k type algorithm is presented in the first part of this paper. The second part of this paper deals with a bistatic SAR experiment performed in October 2003, where two SAR systems of FGAN have been flown on two different airplanes. First bistatic SAR images are presented. Bistatic SAR, SAR processing, omega-k algorithm, bistatic experiments

ARTINO: A New High Resolution 3D Imaging Radar System on an Autonomous Airborne Platform

The new radar system ARTINO (Airborne Radar for Three-dimensional Imaging and Nadir Observation), devel- oped at FGAN-FHR, allows to image a direct overflown scene in three dimensions. Integrated in a small, mobile, and dismountable UAV (Unmanned Aerial Vehicle) it will be an ideal tool for various applications. This paper gives an overview about the ARTINO principle, the raw data simulation, the image formation, the technical realisation, and the status of the experimental system. I. THE ARTINO PRINCIPLE

Potential and limitations of forward-looking bistatic SAR

Bistatic synthetic aperture radar (SAR) operateswith spatially separated transmit and receive antennas that are mounted on separated platforms. Provided that there is an overlap of both antenna footprints, the platforms can move with different velocities in arbitrary directions. A special configuration is given, when the receive antenna looks in forward direction, which is called bistatic forward-looking SAR. Besides the well known advantages of bistatic SAR like the increased information content of the data because of different RCS and scattering characteristics, such a configuration enables high resolution imaging in forward direction, which is not possible with conventional monostatic SAR systems. This paper analyzes a bistatic forward-looking configuration and demonstrates the capability and feasibility of imaging in forward or backward direction using the radar satellite TerraSAR-X as transmitter and the airborne SAR system PAMIR as receiver.

Image quality analysis of the vibrating sparse MIMO antenna array of the airborne 3D imaging radar ARTINO

ARTINO1 is a new radar system, integrated in a small mobile and dismountable experimental UAV2. The side- looking geometry of usual SAR3 systems produces shading effects of the scene to be imaged. ARTINO overcomes this restriction with the ability to image the direct overflown area (Nadir looking) in three dimensions. The effects caused by vibrations of the used sparse MIMO4 antenna array- which is embedded in the wings of the airplane - are discussed with respect to the 3D imaging quality. A correction approach within the image formation process is presented, too.