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igarss_2011_presentation_brcic.ppt
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
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6. 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 Δ TEC [cycles / TECU] 0.89 0.15 0.18 0.012
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10. Split Spectrum Method interferometric phase at carrier frequency Subband Range Spectra Lower Subband Upper Subband non-dispersive topography, atmosphere dispersive ionosphere Optimal subband bandwidth? b = B / 3 (same as split spectrum/delta-k absolute phase estimator)
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12. 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
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15. 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 Range Phase Change [cycles / TECU] BIOMASS 12.5 6 3.2k 0.27 0.89 ALOS-PALSAR 4.5 14 21k 0.13 0.15 4.5 28 42k 0.047 DESDynI / TerraSAR-L 10 80 53k 0.015 Sentinel-1 6 100 110k 0.034 0.18 TerraSAR-X 3.3 100 200k 0.045 0.012 3.3 300 610k 0.0087
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19. 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. 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
22. 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 ( Δ STEC) 0.04 TECU or 0.09 cycles
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Notes de l'éditeur
Intro (rely on Franz’s intro) What: estimate/correct ionospheric phase screen in repeat-pass InSAR Why: significant effects at L-Band (TerraSAR-L, DESDynI) How: split-spectrum & range group-phase delay difference methods What exists: Franz
Swath widths, P 100, L 50, C 250, X 30
Scene 28 x 66 km 46 day repeat cycle 3 s synthetic aperture = 23 km in orbit, 13 km in ionosphere
Multilooking 4 x 25 SSC pixels
Delta-k smoothing: 67 x 30 ~ 2000 interferometric pixels Rewrapped ionospheric phase estimate and DEM compensated phase fringe patterns compare well On ground: 3 dB resolution 3 x 1 km
Range group–phase delay estimate Range group delay from coherent correlation over 64 x 64 SSC pixels Range phase delay from fullband MCF unwrapped phase Smoothed with triangular window
600 m topo , hoa 1 km/cycle topo phase ~0.6 cycles unwrapped fringes ~4 cycles iono phase ~4 cycles ( ΔSTEC of about 2 TECU ) SS Smoothing 32 x 32 ~ 1000 inf pixels 3dB res gnd 6 km x 6 km, iono 2.5 km x 6 km average coherence of 0.2, theoretical standard deviation for SS ionospheric phase 0.065 cycles and ΔSTEC 0.031 TECU RGPD incoherent + coherent CC 128 x 128 ml 18 x 112 3 dB res iono 4 km x 4 km General agreement in trend of ΔSTEC in upper 2/3 of the scene (average coherence 0.25) no agreement in lower 1/3 (average coherence 0.1)