An Experiment of GB-SAR An Experiment of GB-SAR Interferometric Measurement Interferometric Measurement of Target Displacement and of Target Displacement and Atmospheric Correction Atmospheric Correction Hoonyol Lee, Jae-Hee Lee Hoonyol Lee, Jae-Hee Lee Kangwon National University, Korea Kangwon National University, Korea Seong-Jun Cho, Nak-Hoon Sung, Jung-Ho Kim Seong-Jun Cho, Nak-Hoon Sung, Jung-Ho Kim Korea Institute of Geoscience and Mineral Korea Institute of Geoscience and Mineral Resources Resources IGARSS2008, Boston, MA, USA
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Hoonyol Lee, Jae-Hee Lee Kangwon National University, Korea
IGARSS2008, Boston, MA, USA. An Experiment of GB-SAR Interferometric Measurement of Target Displacement and Atmospheric Correction. Hoonyol Lee, Jae-Hee Lee Kangwon National University, Korea Seong-Jun Cho, Nak-Hoon Sung, Jung-Ho Kim Korea Institute of Geoscience and Mineral Resources. - PowerPoint PPT Presentation
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An Experiment of GB-SAR Interferometric An Experiment of GB-SAR Interferometric Measurement of Target Displacement and Measurement of Target Displacement and
Atmospheric CorrectionAtmospheric Correction
Hoonyol Lee, Jae-Hee Lee Hoonyol Lee, Jae-Hee Lee Kangwon National University, KoreaKangwon National University, Korea
Seong-Jun Cho, Nak-Hoon Sung, Jung-Ho KimSeong-Jun Cho, Nak-Hoon Sung, Jung-Ho KimKorea Institute of Geoscience and Mineral ResourcesKorea Institute of Geoscience and Mineral Resources
– “Ground-Based”• Fairly versatile system configuration
– Multiple frequency (L, C, X, Ku, Ka, etc)– Full Polarization (VV, VH, HV, HH)
• Ultimate SAR focusing– Zero Doppler centroid (stationary vehicle and target during Tx/Rx)– Accurate estimation of Doppler rate from geometry
• Topography Mapping: Cross-Track InSAR• Surface Motion: Zero-baseline and short atmospheric path for high temporal
coherency, DInSAR• Useful for new SAR concept design
• GB-SAR Activities– EU and Japan for avalanche, landslide, glacier, building monitoring
GB-SAR System
< Example >Center frequency : 5.3 GHz
Range bandwidth : 600 MHz Range resolution: 25 cmNumber of points : 1601Maximum Range: 200 m Azimuth length : 5 m Azimuth Step : 5 cm Azimuth Resolution: 0.32 degreeAzimuth width: 32 degree Power : 33 dBmPolarization: Full
System Configuration
SAR Focusing Algorithms
Algorithms Advantage Disadvantage Usage
Range-Doppler or ω-k
Widely used for SAR
Memory inefficiency for partial-focusing
Near Range
(full-focusing)
Deramp-FFTEfficient in
memory and CPU time
Distortion in near range
Far Range
(partial-focusing)
Time Domain Exact everywhere Time consuming Everywhere
• Our algorithm in HH polarization at 52% humidity (average of Pipia et al.) is:
33.30 10 R
31.85 10 R
Wavelength Dependency of Phase Delay
• n is constant over the wide range of electromagnetic spectrum (non-dispersive).
• Phase delay is inversely proportional to wavelength.
• Gradient ratio between X and C-band: 1.78
• Wavelength ratio between C and X-band: 1.82
4
Rn
So, what’s the point?
• Merely 11% of the humidity change (47%-58%) between two C-band SAR observations may cause:– a DInSAR-error of 3 mm at 200 m range,– a satellite DInSAR-error of 3 cm (one fringe)
assuming 2 km range propagation through the tropospheric thick moist zone
– 1.5mm DInSAR-error between near-range and far-range (100 m path difference for 2 km lower troposphere) for Envisat IS2
• Care should be taken of when we try to seek a geophysical meaning of one or two fringes.
2 km thick moist layer
Satellite SAR
Conclusion
• We made a SAR system capable of highly accurate consecutive measurements.
• GB-SAR displacement measurement have shown 2-3 mm error with moisture change of 11% (47-58%) at 160 m range.
• Phase/Range vs humidity showed highly linear trend, resulting in a simple atmospheric correction algorithm in terms of humidity.
• Comparison with an X-band experiment (Pipia et al., 2008) confirmed the non-dispersive nature of microwave.
• Merely 11% moisture change both in time and space, for example, is enough to generate one or two fringes for satellite-based InSAR applications.