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IGARSS 2011, Vancouver, CanadaSession: 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
Institut für Methodik der Fernerkundung
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
Institut für Methodik der Fernerkundung
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
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Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
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IGARSS 2011, Vancouver, CanadaSession: 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 kmeffectively constant over SAR scene dimensions
Temporal variations: daily, seasonally, solar cyclesun-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
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IGARSS 2011, Vancouver, CanadaSession: 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 ScreenTEC ΔTEC (master – slave TEC)constant ΔTEC phase gradient in rangespatial variations in ΔTEC modulate ionospheric phase
22
cos
group phase
inc
STECK
f
TECSTEC
[m]
(Slant range TEC)
Ionosphere ~100 – 1000 km
equivalent SAR model thin layer, barycenter 400 km
TEC 13±0.2 STEC 16±0.5
07-07-2007, 18:30 local time68° W 25° S, scene 32 x 57 km
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IGARSS 2011, Vancouver, CanadaSession: 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
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 BIOMASSDESDynI/
TerraSAR-LALOS-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
Existing and future SAR systems: interferometric phase sensitivity to VTEC at 35° incidence angle
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
Institut für Methodik der Fernerkundung
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 8
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IGARSS 2011, Vancouver, CanadaSession: 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 GPSLow res ~100s of kms, little or no spatial resolution over SAR image, ~1 TECU RMSE
Single Image TechniquesAutofocus, Faraday Rotation (Polarimetric data, latitude dependent)
InSAR TechniquesSplit 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 correlationalso exploits differing dispersive/nondispersive frequency behaviour, low resolution
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
Institut für Methodik der Fernerkundung
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 10
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IGARSS 2011, Vancouver, CanadaSession: 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 phaseat carrier frequency
11
1
22
2
1 2 2 1 1 22
2 12
topo iono CC C
C
topo iono CC C
C
ionoC
C
ff
f f
ff
f f
f f f f
f f f
Subband Range Spectra
Lower Subband Upper Subband
2f
b
Cff
1f
B b
2 2 topo ionoC
C CC
f R K STEC
c cf
Split Spectrum Method
non-dispersive topography, atmosphere
dispersive ionosphere
C
Optimal subband bandwidth?
b = B / 3(same as split spectrum/delta-k absolute phase estimator)
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
Institut für Methodik der Fernerkundung
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 12
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IGARSS 2011, Vancouver, CanadaSession: 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
2iono C RC
2 2
topo ionoC C C
C
topo topo iono ionoR R C R C
R K STEC
cf
non-dispersivetopography, atmosphere
phase delay = group delay
dispersive ionosphere
phase delay = – group delay
take differenceperform averaging
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
Institut für Methodik der Fernerkundung
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 14
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IGARSS 2011, Vancouver, CanadaSession: 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 spectrumSubband center frequency error couples dispersive & non-dispersive components
Better performance at low carrier frequencies & high bandwidths
Range group-phase delayPerformance determined by crosscorrelation based group delay estimate
(In)Coherent CC σ is (1.5)2 x less than split-spectrum
22 13 3 1 [ ]
16Cfc TECU
K B N
erroriono iono topoC C Cf
range spectrum with nonuniform weighting
f
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IGARSS 2011, Vancouver, CanadaSession: 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
AveragedRange Phase Change
[cycles / TECU]
BIOMASS 12.5 6 3.2k 0.27 0.89
ALOS-PALSAR4.5 14 21k 0.13
0.154.5 28 42k 0.047
DESDynI / TerraSAR-L 10 80 53k 0.015
Sentinel-1 6 100 110k 0.034 0.18
TerraSAR-X3.3 100 200k 0.045
0.0123.3 300 610k 0.0087
( ) at 0.7ionoC
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IGARSS 2011, Vancouver, CanadaSession: 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 spectrum Range 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
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
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Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 18
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IGARSS 2011, Vancouver, CanadaSession: 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 coherence150.21 W, 69.96 N01-04-2007, 17-05-2007
2. Poor coherence147.40 W, 66.62 N01-04-2007, 17-05-2007
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IGARSS 2011, Vancouver, CanadaSession: 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 coherenceaverage = 0.5
Topographic phase from external DEM
250 m change in topography0.5 cycles at 512 m hamb
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IGARSS 2011, Vancouver, CanadaSession: 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
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IGARSS 2011, Vancouver, CanadaSession: 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
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IGARSS 2011, Vancouver, CanadaSession: 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 spectrumres. 1 km x 1 km
Range group–phase delayres. 2 km x 2 km
ΔSTEC Estimates
average coherence 0.5
split spectrum σ(ΔSTEC)
0.04 TECU or 0.09 cycles
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IGARSS 2011, Vancouver, CanadaSession: 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
Fullbandavg. coherence 0.2
FullbandMCF-PU
Split-spectrumΔSTEC
Split-spectrumionospheric phase
Range group–phase delayΔSTEC
<0.1
0.25
<0.1
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IGARSS 2011, Vancouver, CanadaSession: 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 TECSplit Spectrum Method
Range Group – Phase Delay Method
Theoretical Performance
Experiments with ALOS-PALSAR acquisitions
Summary & Conclusion
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IGARSS 2011, Vancouver, CanadaSession: 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“)