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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 Brcic1, Alessandro Parizzi1, Michael Eineder1, Richard Bamler1 and Franz Meyer2 1 Remote Sensing Technology Institute (IMF), German Aerospace Center (DLR) 2 Geophysical Institute, University of Alaska, Fairbanks Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 2 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 2 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 3 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 3 Ionospheric Effects in InSAR Ionised gases at 50 – 1000 km Yearly Average 2010 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 06:00 local, descending, 0 – 10 TECU 18:00 local, ascending, 0 – 30 TECU IGARSS 2011, Vancouver, Canada Folie 4 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 4 Ionospheric Effects in InSAR Dispersive medium for SAR signals Ionosphere ~100 – 1000 km Group Delay, Phase Advance, Faraday Rotation group phase 2 K STEC STEC [m] f2 equivalent SAR model thin layer, barycenter 400 km TEC (Slant range TEC) cos inc 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 TEC 13±0.2 STEC 16±0.5 07-07-2007, 18:30 local time 68° W 25° S, scene 32 x 57 km IGARSS 2011, Vancouver, Canada Folie 5 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 5 Ionospheric Effects in InSAR Existing and future SAR systems: interferometric phase sensitivity to VTEC at 35° incidence angle Band P L C X Carrier Frequency 435 MHz 1.27 GHz 5.405 GHz 9.65 GHz Agency ESA NASA/DLR JAXA ESA DLR Mission or Sensor BIOMASS DESDynI/ TerraSAR-L ALOS-PALSAR Sentinel-1 TerraSAR-X, TanDEM-X Range Bandwidth [MHz] 6 80 14, 28 100 100, 150, 300 Range Delay [m / TECU] 5.2 0.61 0.034 0.011 Interferometric Phase Advance [cycles / TECU] 7.5 2.6 0.61 0.34 Assumed Swath Width [km] 100 50 250 30 Interferometric range phase change over swath for constant ΔTEC [cycles / TECU] 0.89 0.15 0.18 0.012 IGARSS 2011, Vancouver, Canada Folie 6 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 6 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 7 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 7 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 IGARSS 2011, Vancouver, Canada Folie 8 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 8 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 9 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 9 Split Spectrum Method C topo C interferometric phase at carrier frequency 2 fC R c iono C non-dispersive topography, atmosphere dispersive ionosphere Subband Range Spectra Lower Subband 2K STEC cfC 1 topo C f f1 Ciono C fC f1 2 topo C f f2 Ciono C fC f2 Upper Subband iono C f1 fC f2 b B b f f1 f 2 f 21 f12 2 2 fC f 2 f1 Optimal subband bandwidth? b=B/3 (same as split spectrum/delta-k absolute phase estimator) IGARSS 2011, Vancouver, Canada Folie 10 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 10 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 11 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 11 Range Group – Phase Delay Method C unwrapped interferometric phase at carrier frequency Ctopo 2R Ciono 2 K STEC cfC non-dispersive topography, atmosphere dispersive ionosphere phase delay = group delay phase delay = – group delay shift from crosscorrelation between master and slave R take difference perform averaging topo topo R C iono C iono iono R C C R 2 IGARSS 2011, Vancouver, Canada Folie 12 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 12 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 13 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 13 Theoretical Performance Split spectrum Subband center frequency error couples dispersive & non-dispersive components range spectrum with nonuniform weighting iono error C iono C topo C f f Better performance at low carrier frequencies & high bandwidths 3 3c fC2 1 16K B N 1 2 [TECU ] 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 IGARSS 2011, Vancouver, Canada Folie 14 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 14 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, Sensor Azimuth Resolution [m] Range Bandwidth [MHz] Resolution Cells Averaged (C ) at 0.7 Range Phase Change [cycles / TECU] BIOMASS 12.5 6 3.2k 0.27 0.89 4.5 14 21k 0.13 4.5 28 42k 0.047 DESDynI / TerraSAR-L 10 80 53k 0.015 Sentinel-1 6 100 110k 0.034 3.3 100 200k 0.045 3.3 300 610k 0.0087 iono ALOS-PALSAR TerraSAR-X 0.15 0.18 0.012 IGARSS 2011, Vancouver, Canada Folie 15 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 15 Comparison Split spectrum Computational Performance Filtering & InSAR processing of subbands Statistical Performance Error Behaviour Range group-phase delay Minimal extra effort group delay estimates from coregistration phase delay estimates from fullband PU Better statistical performance (theoretically) 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 IGARSS 2011, Vancouver, Canada Folie 16 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 16 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 17 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 17 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 IGARSS 2011, Vancouver, Canada Folie 18 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 18 Experiments 250 m change in topography 0.5 cycles at 512 m hamb Fullband coherence average = 0.5 Topographic phase from external DEM IGARSS 2011, Vancouver, Canada Folie 19 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 19 Experiments Fullband Phase 6 cycles in unwrapped phase – 0.5 cycles due to elevation = 5.5 cycles in differential phase = 5.5 cycles of ionosphere Fullband differential phase (DEM compensated) Fullband unwrapped phase IGARSS 2011, Vancouver, Canada Folie 20 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 20 Experiments Split Spectrum Estimates Ionospheric phase ~5.5 cycles Ionospheric phase rewrapped Ionospheric phase IGARSS 2011, Vancouver, Canada Folie 21 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 21 Experiments ΔSTEC Estimates average coherence 0.5 split spectrum σ(ΔSTEC) 0.04 TECU or 0.09 cycles Split spectrum res. 1 km x 1 km Range group–phase delay res. 2 km x 2 km IGARSS 2011, Vancouver, Canada Folie 22 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 22 Experiments Low coherence (<0.2) can cause difficulties for MCF-PU Affects both split spectrum and range group – phase delay 0.25 <0.1 Fullband avg. coherence 0.2 Fullband MCF-PU Split-spectrum ionospheric phase Split-spectrum ΔSTEC Range group–phase delay ΔSTEC IGARSS 2011, Vancouver, Canada Folie 23 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 23 Contents Ionospheric Effects in InSAR Estimating TEC Split Spectrum Method Range Group – Phase Delay Method Theoretical Performance Experiments with ALOS-PALSAR acquisitions Summary & Conclusion IGARSS 2011, Vancouver, Canada Folie 24 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 24 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“) IGARSS 2011, Vancouver, Canada Folie 25 Session: TU4.T02.2 - Ionospheric Effects on SAR, PolSAR and InSAR, Tuesday, July 26 Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum Institut für Methodik der Fernerkundung Ionospheric Effects in SAR Interferometry: An Analysis and Comparison of Methods for their Estimation 25