The document evaluates different focusing and motion compensation techniques for processing single-pass airborne polarimetric interferometric synthetic aperture radar (PolInSAR) data at L-band. It finds that omega-k focusing with dual-line motion compensation is sufficient for moderate resolutions but that time domain backprojection with terrain-based motion compensation improves performance for high-resolution and high-squint applications. Future work includes system re-calibration, further PolInSAR performance evaluation, and speeding up the time domain implementation.

1. Accurate Focusing of Single-Pass Airborne InSAR Data at L-band IGARSS 2010 Honolulu, Hawaii, July 26 - 30, 2010 Marcus Schwäbisch, Bryan Mercer, Qiaoping Zhang, Wei Huang Intermap Technologies

2. Overview Motivation Investigated Focusing Options Omega-k and dual-line mocomp vs. single-line mocomp Time domain backprojection Performance Evaluation Focusing Mis-registration Squint handling PolInSAR Conclusion

3. Motivation Goal accurate products from an airborne long-wavelength polarimetric interferometric SAR in an operational scenario Intermap’s TopoSAR L-band single-pass PolInSAR Processing challenges airborne: motion compensation long wavelength: wide azimuth beamwidth, long integration time interferometry: differential phase accuracy PolInSAR: requires high resolution processing to achieve sufficient number of looks operational aspect: requires high squint capability Processing aspects azimuth focusing motion compensation

4. Investigated processing options Omega-k focusing with single-line mocomp Omega-k in principle is an optimum SAR focusing technique without approximations requires data to be acquired along a straight line single-line mocomp is fast and efficient, but non-optimal for significant InSAR baselines Omega-k focusing with dual-line mocomp dual-line mocomp avoids differential effects in interferometric channels center-beam approximation in mocomp still does not avoid focusing degradation caused by FM rate errors Time domain backprojection with integrated mocomp full-aperture solution for mocomp terrain dependent time consuming

5. Single-line vs. dual-line motion compensation FM rate mismatch is being caused whenever the APC position deviates from the straight line requirement leads to defocusing and phase corruption problem in frequency-domain focusing: biases can be compensated, but instantaneous displacements not

6. Analysis Experimental setup L-band single-pass test data from Intermap’s experimental TopoSAR platform various testsites in Western Canada Performance evaluation focusing performance interferometric performance channel mis-registration coherence high squint handling PolInSAR performance

7. TopoSAR single-pass L-band platform log-periodic antenna < -40dB NESZ 3.5 m interferometric baseline 1.2 km swath width 1000 m typical flight altitude 0.25 m azimuth resolution up to 1.1 m range resolution up to 135 MHz (80 MHz nominally) max. system bandwidth 2200 Hz PRF (per channel) quad (HH, HV, VH, VV) Polarization 0.2262 m Wavelength 0.4 kW Peak power

8. L-band Pauli Decomposition Didsbury, AB, Canada 0.25m az resolution 1m resolution @ 4 looks

9. Corresponding Google Earth image

10. Analysis Experimental setup L-band single-pass test data from Intermap’s experimental TopoSAR platform various testsites in Western Canada Performance evaluation focusing performance interferometric performance channel mis-registration coherence high squint performance PolInSAR performance

11. Focusing performance single-line mocomp impulse response 0.5 m resolution 3.5° squint

12. Focusing performance dual-line mocomp impulse response 0.5 m resolution 3.5° squint

13. Focusing performance time domain impulse response 0.5 m resolution 3.5° squint

14. High resolution processing 0.25 m azimuth resolution (> 8 sec azimuth integration time) single-line mocomp dual-line mocomp time domain

15. Channel mis-registration (azimuth) mis-registration in azimuth 20% oversampling (sample size = 0.8  resolution cell size) single-line mocomp dual-line mocomp time domain -1 samples 1

16. Coherence single-line mocomp dual-line mocomp time domain single-pol coherence (HH)

17. High squint handling impulse response for 9.5° squint angle, 0.5 m az resolution single-line mocomp dual-line mocomp time domain

18. PolInSAR performance Edson, AB, Canada forest height and ground topography estimation RVoG model PolInSAR derived tree height PolInSAR derived ground topography Air photo Profile 1 Lidar h 100 Lidar DTM L-band tree height L-band ground

19. Summary and Conclusions We have analyzed various focusing/mocomp options to accurately process single-pass airborne PolInSAR data at L-band Omega-k focusing with dual-line mocomp and center-beam approximation is sufficient for moderate resolution and moderate platform motion Time domain backprojection with terrain-based mocomp greatly improves the performance for high-res and high squint applications Future steps system re-calibration (geometric and polarimetric) PolInSAR performance evaluation speed up the time domain implementation fast backprojection techniques GPU processing