EO Conference’04 - Tokyo - 16/07/2004
PS InSAR analysis with different SAR sensors
Claudio Prati, Fabio Rocca, Alessandro Ferretti
Politecnico di Milano – [email protected]
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Differential InSAR for surface deformation mapping
PS (Permanent Scatterers): distributed and
point-wise scatterers that maintain a
coherent radar signature in time
R1
R2
Bam – Iran: Dec. 26, 2003 earthquake
∆r
PS
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PS
PS
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Permanent Scatterer InSAR
VS (time-Varying Scatterers): distributed
scatterers that do not show a coherent
radar signature over the time gap between
two SAR acquisitions
R1
R2
Arno
Pisa
∆r
Livorno
Migliarino
VS VS
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PS
VS
VS
PS
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Identification of the Permanent Scatterers
PSs can be identified by analyzing the phases of neighboring pixels in
several interferograms.
The relative elevation of each PS is estimated
by means of a linear regression of the
interferometric phases with respect to the
baseline
The relative linear motion component of each
PS is estimated by means of a linear
regression of the interferometric phases with
respect to the time
The residual phases of each PS are due to the
Sub-meter accuracy
Millimeter accuracy
Pi
Po
atmosphere
clutter
geometric decorrelation
temporal change
PS = small residual phases
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Accuracy of the Permanent Scatterers measurements
1. The larger the relative bandwidth
2. The larger the baseline dispersion
3. The larger the number of takes
1. The larger the baseline dispersion
2. The shorter the relative baseline
3. The larger the number of takes
}
}
the smaller the elevation dispersion
the smaller the PS motion error variance
PS elevation and motion accuracy with
lower frequency SARs (λ > 10 cm) are
mainly limited by the SNR (clutter and
ambiguities noise), however the number
of PS increases in rural area.
1. Wide orbital tube during the initial phase of the mission (large baseline dispersion)
2. Narrow orbital tube after the initial phase of the mission (short relative baseline)
3. Images should be systematically acquired (large number of takes in a limited time span).
A synchronized SCANSAR mode allows short revisiting and global coverage
4. C – band for sub-millimeter accuracy in urban areas
5. L – band for sub-centimeter accuracy in rural/vegetated area
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Tokyo: J-ERS PS elevation
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Tokyo: ERS PS elevation
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Tokyo: RADARSAT PS elevation
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PS elevation: RADARSAT, ERS, J-ERS comparison
RADARSAT C-band HH pol.
ERS1/2 C-band VV pol.
J-ERS C-band HH pol.
30 images (ERS-like mode)
24 days revisiting period
2.5 years time interval
680 PS/km2
with coherence > .8
30 images
35 days revisiting period
10 years time interval
270 PS/km2
with coherence > .8
46 images
44 days revisiting period
6 years time interval
240 PS/km2
with coherence > .8
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PS elevation profile
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Accuracy of the measured orbits
2m
40m
750m
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Orbital estimation errors
The PS measurements are exploited as a very large ground antenna that allows to estimate
the baselines with up to 10-20 centimeters accuracy. Much larger systematic errors (as for
Radarsat and JERS) might be due to some orbit propagators inaccuracies.
TS=24d
Baseline errors (meters) as measured from the PS analysis
20
10
0
TE~365.25d
TM~27.32d
-10
-20
The Radarsat baseline error behavior
shows a periodicity that might be
connected to a combination of Earth
(TE~365.25 days) and Moon
revolution period (TM~27.32 days)
sampled with the satellite revisiting
period (TS=24 days) or to a higher
harmonic of the Moon revolution
period sampled at 24 days.
Nice question to Radarsat technical
staff.
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-500
0
500
Baseline errors fitting using Earth revolution, Moon and satellite periodicities
20
10
0
-10
-20
-500
0
days
500
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Permanent Scatterer InSAR: APS estimation
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Tokyo: PS motion - Preliminary Radarsat results
RADARSAT C-band HH pol.
30 images (ERS-like mode)
24 days revisiting period
2.5 years time interval
ERS1/2 C-band VV pol.
30 images
35 days revisiting period
10 years time interval
J-ERS C-band HH pol.
46 images
44 days revisiting period
6 years time interval
Secular trends of baseline errors cause smooth velocity anomalies still to be removed for Radarsat,
absent in ERS, already removed for JERS
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Tokyo: PS motion - comparison
80
60
Radarsat
40
mm
20
0
ERS
-20
-40
-60
1992
JERS
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1996
1998
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Tokyo: PS motion - comparison
40
30
Radarsat
mm
20
ERS
10
0
-10
-20
1992
JERS
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1996
1998
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Hilo volcano: RDARSAT PS motion
RADARSAT C-band HH pol.
26 images (standard beam)
24 days revisiting period
2.5 years time interval
-5 to +5 cm/yr from red to blue
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RADARSAT PS RESULTS: BELRIDGE OIL FIELD (CALIFORNIA)
AVERAGE LOS DISPLACEMENT RATE
Color code: up to –160 mm/yr (dark red)
Background layer: Fine Beam MIR Map
Area: ~75 km2 # PS ~4500
Average PS density: ~60 PS/km2
• 22 FINE BEAM RADARSAT images (March 2000 – February 2002)
• Incidence angle: ~39 deg (beam F1), Resolution: 8.3 m x 8.4 m
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RADARSAT PS RESULTS: BELRIDGE OIL FIELD (CALIFORNIA)
3D view of the average deformation rate (superimposed on the multi-image
reflectivity map) highlighting the main and secondary subsidence bowls
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RADARSAT PS RESULTS: BELRIDGE OIL FIELD (CALIFORNIA)
LOS velocity: -163.3 mm/yr
LOS velocity: -69.3 mm/yr
LOS velocity: -26.9 mm/yr
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LOS velocity: 0 mm/yr
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ERS: 3 vs 35 days revisiting – PS elevation
35 days
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ERS: 3 vs 35 days revisiting – PS motion
35 days
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CONCLUSIONS
•
•
•
DINSAR quality is almost independent of the radar frequency, provided that the
wavelength be shorter than 10cm.
Longer wavelengths require quadratic higher SNR to get the same accuracy.
S an C bands are most indicated to get sub-millimeter motion and sub-meter
elevation accuracy in urban areas. X band does not improve S or C band results while
increasing unwrapping costs and decreasing penetration.
•
L band is useful to get sub-centimeter motion and meter elevation accuracy in
rural/vegetated areas.
•
The PS technique yields several advantages with respect to standard InSAR:
1.
2.
3.
4.
•
Allows long surveys
Precise baselines estimation
Atmospheric Phase Screen estimates
Elevation and motion of single scatterers
The PS potential is fully exploited if:
1. SAR images with the same acquisition mode are acquired regularly and often
2. Orbits are known with sub-meter accuracy
3. The orbital tube is wider at the beginning of the mission
Mode changes (frequency, angle, orbit …) entail archive regeneration (min 15 images)
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