Bistatic TerraSAR-X/F-SAR Spaceborne–Airborne SAR Experiment: Description, Data Processing, and Results

Abstract

We report about the first X-band spaceborneairborne bistatic synthetic aperture radar (SAR) experiment, conducted early November 2007, using the German satellite TerraSAR-X as transmitter and the German Aerospace Center's (DLR) new airborne radar system F-SAR as receiver. The importance of the experiment resides in both its pioneering character and its potential to serve as a test bed for the validation of nonstationary bistatic acquisitions, novel calibration and synchronization algorithms, and advanced imaging techniques. Due to the independent operation of the transmitter and receiver, an accurate synchronization procedure was needed during processing to make high-resolution imaging feasible. Precise phase-preserving bistatic focusing can only be achieved if time and phase synchronization exist. The synchronization approach, based on the evaluation of the range histories of several reference targets, was verified through a separate analysis of the range and Doppler contributions. After successful synchronization, nonstationary focusing was performed using a bistatic backprojection algorithm. During the campaign, stand-alone TerraSAR-X monostatic as well as interoperated TerraSAR-X/F-SAR bistatic data sets were recorded. As expected, the bistatic image shows a space-variant behavior in spatial resolution and in signal-to-noise ratio. Due to the selected configuration, the bistatic image outperforms its monostatic counterpart in almost the complete imaged scene. A detailed comparison between monostatic and bistatic images is given, illustrating the complementarity of both measurements in terms of backscatter and Doppler information. The results are of fundamental importance for the development of future nonsynchronized bistatic SAR systems.

A Modified Synchronization Method for Bistatic Sar

“…BiSAR system has many advantages, including high flexibility in designing SAR missions, higher signal to noise ratio (SNR), etc. [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. As a typical BiSAR configuration, spaceborne/stationary configuration fixes the transmitter sub-system on the satellite and the receiver sub-system on the ground, as shown in Figure 1.…”

“…Reference target is used in [18] to achieve synchronization. A dedicated channel that receives signal directly from transmitter can also provide synchronization information [16][17][18][19].…”

“…Reference target is used in [18] to achieve synchronization. A dedicated channel that receives signal directly from transmitter can also provide synchronization information [16][17][18][19]. However, the above-mentioned methods have limitation in practice when the parameters of the transmitted signal are unknown, and the direct signal has serious saturation, or the gain of the direct signal (GDS) is very low.…”

Performance Analysis of Bistatic Interferometer Based on Spaceborne Sar

“…Over the last few years, the BSAR synchronization and imaging technology have been studied well [1][2][3][4][5][6]. Several experiments with different topologies have been conducted, and a number of valuable results have been published [7][8][9][10]. Research is now moving towards the exploitation of BSAR application, including interferometric measurement and coherent change detection [11][12][13][14].…”

“…Usually, the revisit cycle of spaceborne SAR is quite long (several days or more), and this system could only work for several seconds during the revisit [7,8]. Therefore, to avoid echo window synchronization issues and to enhance the reliability of experiments, a conservative continuous data acquisition mode is applied in BIBASS.…”