The document discusses experiments performed using TerraSAR-X (TSX) and TanDEM-X (TDX) satellites to demonstrate capabilities of distributed imaging with bi-static SAR systems. Three key experiments are described: 1) Super resolution in range was achieved through step-frequency acquisitions from both satellites, combining the signals coherently to increase range resolution beyond the individual satellite limitations. 2) Super resolution in azimuth used the satellites' Doppler offsets to synthesize a signal with twice the azimuth resolution of either satellite alone. 3) Quad-polarized images were synthesized from dual-polarized acquisitions from each satellite, using one polarization for imaging and the other for calibration.

1. Pau Prats , Paco López-Dekker, Francesco De Zan, Steffen Wollstadt, Markus Bachmann, Ulrich Steinbrecher, Rolf Scheiber, Andreas Reigber, Gerhard Krieger Microwaves and Radar Institute (HR) German Aerospace Center [email_address] Distributed Imaging with TSX and TDX

2. Motivation Future SAR missions will exploit bi- and multistatic SAR systems. Such systems increase the potential, reliability and flexibility of future SAR missions. Potential: frequent monitoring, wide-swath imaging, single-pass interferometry, enhanced products (e.g. in terms of resolution). Perform new experiments! ;c) G. Krieger and A. Moreira, “Spaceborne bi- and multistatic SAR: potential and challenges”, IEE Proc.-Radar Sonar Navig., vol. 153, no. 3, June 2006.

3. VU > Alberto Moreira SAR Interferometer Close formation Global DEM (HRTI-3) T erraSAR-X a dd o n for D igital E levation M easurements

4. TanDEM-X: Secondary Mission Objectives VU > Alberto Moreira Bistatic SAR Imaging Super Resolution Polarimetric SAR Interferometry Ground Moving Target Indication SAR Tomography Sea ice monitoring B 1 B 2 B 3     Crossed-orbits   Double Differential Interferometry Digital Beamforming

5. Some Experiments with Distributed Imaging Demonstration of distributed imaging with the following experiments: Range-resolution enhancement Azimuth-resolution enhancement Quad-pol synthesis with dual-pol acquisitions Digital beamforming Elaborated manual commanding of each experiment Experiments performed during the monostatic commissioning phase: 20 km ~ 3 s TSX TDX Baseline needs to be compensated

6. TanDEM-X Commissioning Phase June‘10 July‘10 Aug‘10 Sep‘10 Oct‘10 Nov‘10 Dec‘10 Early Orbit Phase Grg Segment Checkout Bi-static Commissioning Phase 20 km Formation TDX Orbit Drift 16.000 km  20 km Close Helix-Formation 300-400 m Launch 21 June DEM Acquisition First SAR Image 24 June (MET +3.6) First DEM 16 July (MET +25) TDX Monostatic Comm. Phase 6 Months Commissioning Phase First close formation DEM 19 October (MET +124) First bi-static SAR image 8 August (MET +48) First single-pass bi-static DEM 2 October (MET +107)

7. Super Resolution in Range: Step-Frequency with TSX and TDX Limitation: RF filter allows maximum band of 300 MHz Advantages within limitation: Increased SNR Data rate distributed among satellites Baseline compensation for proper coherent combination Negligible spectral shift for current configurations (but nevertheless considered) f 0 -  f f 0 +  f f 0 f r f r f r  TSX TDX 300 MHz

8. Super Resolution in Range: Step-Frequency with TSX and TDX Coregistration Common-band spectrum interferogram

9. Super Resolution in Range: Experimental Setup Data takes over Sydney, Australia, on August 15 and 26, 2010

10. Super Resolution in Range: Experimental Results azimuth  range 

11. Super Resolution in Range: Experimental Results (II) Common-band interferogram azimuth  range 

12. Super Resolution in Range: Experimental Results (III) azimuth  range 

13. Super Resolution in Range: Experimental Results (IV) azimuth  range 

14. Super Resolution in Range: Experimental Results (V) azimuth  range 

15. Super Resolution in Range: Experimental Results (VI) Interferometric coherence between synthesized images Interferometric phase between synthesized images azimuth  range 

16. Super Resolution in Azimuth f DC,1 f DC,2 f DC,mean f a f a f a  TSX TDX

17. Super Resolution in Azimuth: Experimental Setup Data take over Neustrelitz, Germany, on September 20, 2010

18. Super Resolution in Azimuth: DTAR Analysis TDX DTAR: -21.67 dB TSX DTAR: -21.04 dB Maximum bandwidth DTAR: -19.91 dB Twice the resolution DTAR: -21.42 dB

19. Super Resolution in Azimuth: Experimental Results (I) azimuth  range 

20. Super Resolution in Azimuth: Experimental Results (II) Common-band interferogram azimuth  range 

21. Super Resolution in Azimuth: Experimental Results (III) azimuth  range 

22. Super Resolution in Azimuth: Experimental Results (IV) azimuth  range 

23. Super Resolution in Azimuth: Experimental Results (V) azimuth  range  azimuth  range 

24. Super Resolution in Azimuth: Experimental Results (VI) Measured resolutions over a corner reflector: TSX: 2.97m TDX: 2.97 m Combined: 1.49 m

25. Quad-Pol Synthesis with Dual-Pol Acquisitions Each satellite acquires a co-pol and a cross-pol channel, e.g. HH-VH and HV-VV The cross-pol channel is used to estimate the calibration phase Better SNR and DTAR when compared to the experimental quad-pol product using the dual receive antenna (DRA) mode DLR’s E-SAR example: quad-pol synthesis at C-band with repeat-pass dual-pol acquisitions [1] E-SAR [1] R. Scheiber et al. , “Radar data processing, quality analysis and level-1b product generation for AGRISAR and EAGLE campaigns,” in AGRISAR and EAGLE Campaigns Final Workshop, Noordwijk, The Netherlands, Oct. 15-16 2007.

26. Quad-Pol Synthesis: Experimental Results New acquisitions performed in bistatic mode are on their way. azimuth  range 

27. Conclusion & Future Work Proof of concept of several experiments with TSX and TDX Range-resolution enhancement Azimuth-resolution enhancement Quad-pol synthesis with dual-pol acquisitions Qual-pol synthesis with dual-pol acquisitions using bistatic data (close formation) Further performance analyses, especially for the azimuth case By doubling the PRF one can obtain simultaneously a resolution improvement in both dimensions Digital beamforming with an interferometric baseline

28. Thank you for your attention! VU > Alberto Moreira