1. IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26, 15:20 - 17:00 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Ramon Brcic 1, Alessandro Parizzi 1, Michael Eineder 1, Richard Bamler 1 and Franz Meyer 2 1 Remote Sensing Technology Institute (IMF), German Aerospace Center (DLR) 2 Geophysical Institute, University of Alaska, Fairbanks

2. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 2 2 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

3. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 3 3 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

4. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 4 4 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Ionospheric Effects in InSAR Ionised gases at 50 – 1000 km Spatial variations: typically over >100 km effectively constant over SAR scene dimensions Temporal variations: daily, seasonally, solar cycle sun-synchronous orbits reduce temporal variation Scintillation: rapid temporal & spatial changes Yearly Average 2010 06:00 local, descending, 0 – 10 TECU 18:00 local, ascending, 0 – 30 TECU

5. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 5 5 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Ionospheric Effects in InSAR Dispersive medium for SAR signals Group Delay, Phase Advance, Faraday Rotation SAR images: location, phase shifts constant TEC STEC increases from near to far range group delay & phase advance increase Repeat-pass interferogram: focus on Ionospheric Phase Screen TEC ΔTEC (master – slave TEC) constant ΔTEC phase gradient in range spatial variations in ΔTEC modulate ionospheric phase Ionosphere ~100 – 1000 km equivalent SAR model thin layer, barycenter 400 km TEC 13±0.2STEC 16±0.5 07-07-2007, 18:30 local time 68° W 25° S, scene 32 x 57 km

6. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 6 6 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Ionospheric Effects in InSAR BandPLCX Carrier Frequency435 MHz1.27 GHz5.405 GHz9.65 GHz AgencyESANASA/DLRJAXAESADLR Mission or SensorBIOMASS DESDynI/ TerraSAR-L ALOS-PALSARSentinel-1TerraSAR-X, TanDEM-X Range Bandwidth [MHz]68014, 28100100, 150, 300 Range Delay [m / TECU] 5.20.610.0340.011 Interferometric Phase Advance [cycles / TECU] 7.52.60.610.34 Assumed Swath Width [km] 1005025030 Interferometric range phase change over swath for constant ΔTEC [cycles / TECU] 0.890.150.180.012 Existing and future SAR systems: interferometric phase sensitivity to VTEC at 35° incidence angle

7. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 7 7 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

8. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 8 8 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Estimating TEC / Ionospheric Phase Screen Global Ionospheric Models (GIMs) from GPS Low res ~100s of kms, little or no spatial resolution over SAR image, ~1 TECU RMSE Single Image Techniques Autofocus, Faraday Rotation (Polarimetric data, latitude dependent) InSAR Techniques Split Spectrum or Delta-k [Rosen, Freeman, …] exploit different behaviour of dispersive/nondispersive components in frequency Range group – phase delay [Meyer, Bamler] nondispersive components have same sign, dispersive components have opposite sign Subband correlation also exploits differing dispersive/nondispersive frequency behaviour, low resolution

9. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 9 9 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

10. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 10 10 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation interferometric phase at carrier frequency Subband Range Spectra Lower SubbandUpper Subband Split Spectrum Method non-dispersive topography, atmosphere dispersive ionosphere Optimal subband bandwidth? b = B / 3 (same as split spectrum/delta-k absolute phase estimator)

11. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 11 11 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

12. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 12 12 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Range Group – Phase Delay Method unwrapped interferometric phase at carrier frequency shift from crosscorrelation between master and slave non-dispersive topography, atmosphere phase delay = group delay dispersive ionosphere phase delay = – group delay take difference perform averaging

13. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 13 13 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

14. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 14 14 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Theoretical Performance Split spectrum Subband center frequency error couples dispersive & non-dispersive components Better performance at low carrier frequencies & high bandwidths Range group-phase delay Performance determined by crosscorrelation based group delay estimate (In)Coherent CC σ is (1.5)2 x less than split-spectrum range spectrum with nonuniform weighting

15. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 15 15 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Theoretical Performance Theoretical standard deviation of split-spectrum ΔSTEC and ionospheric phase for various SAR systems. Averaging over constant area of 1 km slant range x 1 km azimuth. Mission, SensorAzimuth Resolution [m]Range Bandwidth [MHz]Resolution Cells Averaged Range Phase Change [cycles / TECU] BIOMASS12.563.2k0.270.89 ALOS-PALSAR 4.51421k0.13 0.15 4.52842k0.047 DESDynI / TerraSAR-L108053k0.015 Sentinel-16100110k0.0340.18 TerraSAR-X 3.3100200k0.045 0.012 3.3300610k0.0087

16. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 16 16 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Comparison Split spectrumRange group-phase delay Computational Performance Filtering & InSAR processing of subbands Minimal extra effort group delay estimates from coregistration phase delay estimates from fullband PU Statistical Performance Better statistical performance (theoretically) Error Behaviour Identical workflow for both subbands common non-dispersive errors cancel Different workflow for group & phase delay estimates common non-dispersive erros may not cancel 2 x subband PU more chance of error 1 x fullband PU less chance of error Sensitivity to range center frequency error

17. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 17 17 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

18. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 18 18 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Experiments L-Band ALOS-PALSAR acquisitions over Alaska known to contain significant ionosphere (provided by Americas ALOS Data Node (AADN) and JAXA) PALSAR PLR-mode, 14 MHz quad pole, HH channel 1. Good coherence 150.21 W, 69.96 N 01-04-2007, 17-05-2007 2. Poor coherence 147.40 W, 66.62 N 01-04-2007, 17-05-2007

19. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 19 19 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Experiments Fullband coherence average = 0.5 Topographic phase from external DEM 250 m change in topography 0.5 cycles at 512 m h amb

20. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 20 20 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Experiments Fullband differential phase (DEM compensated) 6 cycles in unwrapped phase – 0.5 cycles due to elevation = 5.5 cycles in differential phase = 5.5 cycles of ionosphere Fullband unwrapped phase Fullband Phase

21. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 21 21 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Experiments Ionospheric phase rewrapped Ionospheric phase Split Spectrum Estimates Ionospheric phase ~5.5 cycles

22. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 22 22 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Experiments Split spectrum res. 1 km x 1 km Range group–phase delay res. 2 km x 2 km ΔSTEC Estimates average coherence 0.5 split spectrum σ(ΔSTEC) 0.04 TECU or 0.09 cycles

23. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 23 23 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Experiments Low coherence (<0.2) can cause difficulties for MCF-PU Affects both split spectrum and range group – phase delay Fullband avg. coherence 0.2 Fullband MCF-PU Split-spectrum ΔSTEC Split-spectrum ionospheric phase Range group–phase delay ΔSTEC <0.1 0.25 <0.1

24. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 24 24 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion

25. Institut für Methodik der Fernerkundung Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Folie 25 25 IGARSS 2011, Vancouver, Canada Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation Summary & Conclusion Compensation of ionospheric phase for InSAR vital at P and L-Band Estimation theoretically possible across P, L, C and even X-Band Ionospheric phase screen estimation for repeat-pass InSAR confirmed with successful L-Band experiments Given sufficient coherence for reliable phase unwrapping, split-spectrum and range group–phase delay approaches give similar results Current / future work: Comparison with other methods Fusion of all methods to obtain a better estimate (TH3.T02, Thursday, 13:20, Meyer et. al. Potential contributions of the DESDynI mission to ionospheric research)