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DTM Extraction Beneath Canopy Using L- and P-Band Data from INDREX-II:
Preliminary Results
Presented to the PolInSAR Workshop: Frascati, ItalyJanuary 24, 2007
Bryan Mercer, Qiaoping Zhang
Intermap Technologies Corp.
Calgary, Canada
Acknowledgements:
ESA (Malcolm Davidson), DLR, WUR / SARVision
Alberta Ingenuity Fund
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Contents
IntroductionRationale and Objectives
The Approach
Current results
Issues to be Resolved
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Rationale and Objectives
Extraction of ground elevation (DTM) beneath canopyUseful accuracy desired ~ 2-3 meters RMSEPrevious P-Band experience with TopoSAR systemHow does L-Band performance compare?
Opportunity, through ESA, to use INDREX-II data setL- and P-Band quad-pol, interferometric dataGround truth
Objectives of this activity:To compare DTM performance of P- and L-Band To understand the issues and sensitivities with respect to various factors such as forest height and density, slope etcCurrently at an early stage
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Previous Work with TopoSAR SystemCapitol Forest Elevation Profiles
145
150
155
160
165
170
175
180
185
0 100 200 300 400 500 600 700 800
Cross SectionM
eter
s
Meters
LIDAR ‘Truth’ P-Band
X-Band
30 m
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The Approachassume RVOG* model applicable,
extract ground phase Φ
* Treuhaft and Siqueira (2000), Papathanassiou and Cloude (2001)
Real
Imaginary
+*
ΦxΦ = κZ Z0
= Ground Phase
= ground/volume ratiois polarization dependent
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The Reality
γobs = γv γsnr γt γrgsp ...~ ~ ~
INDREX-II Final Report to ESAIrena Hjansek, DLRDirk Hoekman, WUR
≈ 1 We hope!
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Process Summary
L- and P- BandCo-registered SLC pairs
(plus ancillary info)
Coherence Optimization
Coherence
X-BandGeocoded
DSM and image
GPS GroundElevations
CorrectionSurface
Or NormalizationDEM
Phase Unwrap Unit Circle Phase Projection
DEM
INDREX
ThisWork
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The ‘Ideal’ Test Area(for our purpose)
Contains:Patches of alternating bare and forested areasFlat and sloped samplesSamples of varying but homogeneous canopy heights
Ground truth Air Photos (geocoded)Ground photos (georeferenced)Tree height/density/biomass samplesA truth DTM (at the 1 m level or less)
• Lidar would be great (but not available)Radar data
L- and P-Band files complete‘Good’ KzNo temporal decorrelation, good SNR
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Location of Test Sites
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Samboja Lestari (a compromise)
Segment 1P-Band Quad-pol
Image
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X-Band DSMTest Area
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The P- and L-Band Interferometric Data
P-Band Baselines nominally 15 m and 30 m
P15: KZ = - 0.026 rad / mP30: KZ = - 0.079 rad / mP-Band DEM applied directly from interferometric phase (assumes large ‘m’)
L-Band Baselines nominally 5 m and 8 m
L5: KZ = - 0.059 rad / mL8: KZ = -0.061 rad / mL-Band DEMs computed from unit circle projection of best fit among the 3 optimum complex coherences
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Difference Surface: (X – P30) Before Correction
Test Area
meters
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Test Area
Tree Heights 8 – 16 meters
XVVMagnitude
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Test Area: Then (2001) and Now (2004)
IKONOS (2001)
E-SAR X-Band (2004)
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X-Band DSM
(m)
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P-Band DEM 30 m Baseline (P30)Kz = 0.079 rad/m
(m)
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P-Band DEM 15 m Baseline (P15)Kz = 0.026 rad/m
(m)
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Difference Surface (X – P30)
(m)
meters
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Selected Profile Lines on X-Band ORI
Tree measurements
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P30 Profile Line 01
Measured tree height: 11.9m±3.7m
P-Band (30 m)
X-Band
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P30 Cross Profile Line 03
Measured tree height: 11.9m±3.7m
X-Band
P-Band (30m)
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P30 Cross Profile Line 04
Measured tree height: 13.3m±2.8m
P-Band (30m)
X-Band
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L-Band Initial Results
From unit circle projectionWhat do we expect to see?
Observed optimized coherence magnitudes
Observed points on unit circle5 and 8 m baselinesSeparation ?
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Test Area of Interest: L-Band, Bn = 5.4 mKz = 0.073 rad/m, σ = 0.202 m-1 (0.8 db/m)
Complex Coherence for (m/I1) = 0.01, 0.03, 0.10, 0.3, 1.0, 3, 10, 30, 100
as function of canopy height
-1.0
-0.8
-0.5
-0.3
0.0
0.3
0.5
0.8
1.0
-1.0 -0.8 -0.5 -0.3 0.0 0.3 0.5 0.8 1.0
Real
Imag
inar
y
h=30 mh=20 mh=10 mh=1 m
m/I1 = 0.01
m/I1 = 1.0
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Test Area of Interest: L-Band, Bn = 5.4 m Kz = 0.073 rad/m, σ = 0.096 m-1 (0.4 db/m)
Complex Coherence for (m/I1) = 0.01, 0.03, 0.10, 0.3, 1.0, 3, 10, 30, 100
as function of canopy height
-1.000
-0.750
-0.500
-0.250
0.000
0.250
0.500
0.750
1.000
-1.000 -0.750 -0.500 -0.250 0.000 0.250 0.500 0.750 1.000
Real
Imag
inar
y
h=30 mh=20 mh=10 mh=1 m
m/I1 = 0.01
m/I1 = 1.0
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Test Area of Interest: L-Band, Bn = 5.4 mKz = 0.073 rad/m, σ = 0.047 m-1 (0.2 db/m)
Complex Coherence for (m/I1) = 0.01, 0.03, 0.10, 0.3, 1.0, 3, 10, 30, 100
as function of canopy height
-1.000
-0.750
-0.500
-0.250
0.000
0.250
0.500
0.750
1.000
-1.000 -0.750 -0.500 -0.250 0.000 0.250 0.500 0.750 1.000
Real
Imag
inar
y
h=30 mh=20 mh=10 mh=1 m
m/I1 = 0.01
m/I1 = 1.0
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Test Area of Interest: L-Band, Bn = 5.4 mKz = 0.073 rad/m, σ = 0.023 m-1 (0.1 db/m)
Complex Coherence for (m/I1) = 0.01, 0.03, 0.10, 0.3, 1.0, 3, 10, 30, 100
as function of canopy height
-1.000
-0.750
-0.500
-0.250
0.000
0.250
0.500
0.750
1.000
-1.000 -0.750 -0.500 -0.250 0.000 0.250 0.500 0.750 1.000
Real
Imag
inar
y
h=30 mh=20 mh=10 mh=1 m
m/I1 = 0.01
m/I1 = 1.0
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L-Band Coherence Mag: Opt3, 5 m Baseline, Kz = -0.06 rad/m
Bare Area
Forest
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L-Band Coherence Mag: Opt25 m Baseline, Kz = -0.06 rad/m
Bare Area
Forest
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L-Band Coherence Mag: Opt15 m Baseline, Kz = -0.06 rad/m
Bare Area
Forest
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Selected Locations for Complex Coherence Plotting
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Observed Complex Coherence L-Band 8m baseline, Test Point 10
Kz = 0.06 rad/m
Pi/2 = 26 m
Note: HV phase above HH, below VV
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Observed Complex Coherence L-Band 8m baseline, Test Point 9
Kz = 0.06 rad/m
Pi/2 = 26 m
Note: poor separation
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Summary and IssuesStarted work on the extraction of ground elevation from INDREX-II P-Band and L-Band data The P-Band surfaces within the forest appear plausible when normalized locally to X-Band DSM.
Additional ground truth (particularly lidar) is needed for validation
Need to resolve preliminary L-Band coherence issues that are contrary to expectation and to other INDREX inversion results
Poor phase separation in many cases VH bracketed by HH and VVUnlikely that the effect is caused by SNR Possibly temporal de-correlation but unlikely