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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 HuangIntermap Technologies
© 2008 Intermap Technologies. All rights reserved.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
© 2008 Intermap Technologies. All rights reserved.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
© 2008 Intermap Technologies. All rights reserved.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
© 2008 Intermap Technologies. All rights reserved.5
Single-line vs. dual-line motion compensation
FM rate mismatch is being caused whenever the APC position deviates from the straight line requirementleads to defocusing and phase corruptionproblem in frequency-domain focusing: biases can be compensated, but instantaneous displacements not
© 2008 Intermap Technologies. All rights reserved.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
© 2008 Intermap Technologies. All rights reserved.7
TopoSAR single-pass L-band platform
< -40dBNESZ
3.5 minterferometric baseline
1.2 kmswath width
1000 mtypical flight altitude
0.25 mazimuth resolution
up to 1.1 mrange resolution
up to 135 MHz
(80 MHz nominally)
max. system bandwidth
2200 HzPRF (per channel)
quad (HH, HV, VH, VV)
Polarization
0.2262 mWavelength
0.4 kWPeak power
log-periodic antenna
© 2008 Intermap Technologies. All rights reserved.8
L-band Pauli Decomposition
Didsbury, AB, Canada
0.25m az resolution
1m resolution @ 4 looks
© 2008 Intermap Technologies. All rights reserved.9
Corresponding Google Earth image
© 2008 Intermap Technologies. All rights reserved.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
© 2008 Intermap Technologies. All rights reserved.11
Focusing performance
single-line mocomp
impulse response
0.5 m resolution
3.5° squint
© 2008 Intermap Technologies. All rights reserved.12
Focusing performance
dual-line mocomp
impulse response
0.5 m resolution
3.5° squint
© 2008 Intermap Technologies. All rights reserved.13
Focusing performance
time domain
impulse response
0.5 m resolution
3.5° squint
© 2008 Intermap Technologies. All rights reserved.14
High resolution processing
0.25 m azimuth resolution (> 8 sec azimuth integration time)
single-line mocomp dual-line mocomp time domain
© 2008 Intermap Technologies. All rights reserved.15
single-line mocomp dual-line mocomp time domain
Channel mis-registration (azimuth)
mis-registration in azimuth
20% oversampling (sample size = 0.8 × resolution cell size)
-1 samples 1
© 2008 Intermap Technologies. All rights reserved.16
Coherence
single-line mocomp dual-line mocomp time domain
single-pol coherence (HH)
© 2008 Intermap Technologies. All rights reserved.17
High squint handling
impulse response for 9.5° squint angle, 0.5 m az resolution
single-line mocomp dual-line mocomp time domain
© 2008 Intermap Technologies. All rights reserved.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
108510901095
110011051110
111511201125
1130113511401145
0 100 200 300 400 500 600
Cross Section
Meter
s
Meters
Lidar h100
Lidar DTM
L-band tree height
L-band ground
© 2008 Intermap Technologies. All rights reserved.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