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TANDEM-X: DEM ACQUISITION IN THE THIRD YEAR ERA
D. Borla Tridon, M. Bachmann, D. Schulze, C. J. Ortega Miguez, M. D. Polimeni, M. Martone
and TanDEM-X Team
Microwaves and Radar Institute, DLR
5th International Conference on Spacecraft FormationFlying Missions and Technologies
29.05.2013
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Outline
Overview about TanDEM-X Mission
TanDEM-X Global DEM Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year
AntarcticaDifficult Terrain
Conclusions
Slide 2 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Outline
Overview about TanDEM-X Mission
TanDEM-X Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year
AntarcticaDifficult Terrain
Conclusions
Slide 3 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Slide 4
TerraSAR-X-add-on for Digital Elevation Measurements
TerraSAR-X / TanDEM-X:• German Earth observation SAR satellites• Public Private Partnership (PPP) • X-band @ 9.65 GHz• Multi-mode highly flexible operation•TSX-1 Launched on June 2007• TDX-1 Launched on June 2010• 514 km dusk/dawn orbit
Overall Mission Goals• acquisition of a global DEM according to Level-3 standard
• generation of local DEMs withLevel-4 like quality
• demonstration of innovative bistatic imaging techniques and applications
Spatial Resolution Absolute Vertical Accuracy(90%)
Relative Vertical Accuracy(point-to-point in 1° cell, 90%)
DTED-1 90 m x 90m < 30 m < 20 m
DTED-2 30 m x 30m < 18 m < 12 m
TanDEM-X 12 m x 12m < 10 m < 2 m
Level-4 6 m x 6m < 5 m < 0.8 m
Slide 4 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Helix FormationSlide 5 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Cross-Track Interferometry for DEM Acquisition
B
H
z
TanDEM-XφUnwrapping
DEM
Image1 Image 2
TerraSAR-X
Interferogram
Slide 6 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Outline
Overview about TanDEM-X Mission
TanDEM-X Global DEM Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year
AntarcticaDifficult Terrain
Conclusions
Slide 7 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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TanDEM-X Global DEM Acquisition Plan
1st Global Coverage• Small baseline (~200 m)• HoA* ~ 45 m
2010
Commissioningphase
2011
1st global coverage
2012 2013
2nd Global Coverage• Increased baseline (~300 m)• HoA* ~ 30 m
Combination:• Dual Baseline Phase Unwrapping• Improved Height Accuracy
*HoA: Height of Ambiguity ↔ 2π Interferometric Phase
2nd globalcoverage
Additional Acquisitions & Special Science
Additional Acquisitions (3rd year)• Difficult terrain to account
for shadow & layover• Different viewing
geometry• Antarctica
Secondary Mission Goals• Science acquisitions with special
formations• Higher resolution DEMs
with local extend
2014
Slide 8 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Interferometric Coherence of 1st Year120000 scene (1 scene = 50x30 km2)
Mean land coherence: 91.8% higher than 0.6 (“Good”-Quality Flag: 87.6%)
Slide 9 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
Forest: Volume Decorrelation
Deserts: Low SNR
Solid Surface:High Coherence
Mountains:Shadow/Layover
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Formation Flying Configuration
1st year 2nd year 3rd year
Height of Ambiguity ↔ 2π Interferometric Phase large baseline ↔ small HoA ↔ small rel. height errorPhase of libration: relative ascending node – relative perigee
Slide 10 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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DEM Acquisition Timeline Derivation
LandMask
Satellite resources/downlink
Desired baseline (HoA)
Beam definition
Acquisition Timeline derivation: orbit usage
Flight Dynamics(DLR-GSOC)
Helix OptimizationFormation
parameters
Acquisition param.: PRF, duty cycle, energy, memory
Performance param.: SNR, ambiguities,
coherence
Acquisition parameters optimization
Mission Planning(DLR-GSOC)
TanDEM-X Timeline: start/stop time, beam
TanDEM-X orders
Slide 11 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Outline
Overview about TanDEM-X Mission
TanDEM-X Global DEM Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year
AntarcticaDifficult Terrain
Conclusions
Slide 12 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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AntarcticaLeft-Looking acquisitions required -> low energy absorption by solar panels
O‘Higgins
Downlink & on-board memory limited (TDX:768 GBit, TSX:384 GBit)
Eclipse between May and August -> less energy on the solar panels
Vertical dist = 300 mHorizontal dist = 230 m
HoA
Acquisition in winter in Southern Hemisphere to avoid ice melt and low quality data
=> Acquisitions in the beginning of May
Slide 13 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Antarctica
Left-Looking acquisitions over a radius of 1300 km
Slide 14 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
Right-Looking acquisitions in the outer region
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Outline
Overview about TanDEM-X Mission
TanDEM-X Global DEM Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year
AntarcticaDifficult Terrain
Conclusions
Slide 15 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Difficult Terrain: Deserts and Mountainous Regionsto be acquired in the Third Year
- Shadow and Layover- Desert
Slide 16 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Difficult Terrain: Mountainous Regions
Steep and rough surfaces=> Phase unwrapping errors=> HoA > 85 m required
Shadow and Layover effects
Slide 17 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Difficult Terrain: Mountainous Regions
Shadow
ShadowLayover
Descending
Ascending
Andes
Shadow and Layover effects
=> Different viewing geometry:North descending / South ascending
Steep and rough surfaces=> Phase unwrapping errors=> HoA > 85 m required
Slide 18 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Difficult Terrain: Deserts
Deserts: low SNR => low coherence => high relative height error
Rocky deserts present difficult topography=> acquisition with different viewing geometry
as for mountainous regions
Sandy deserts require small incidence angle:between 14o and 28o (nominal 28o – 48o)
Slide 19 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Formation Flying Configuration
1st year 2nd year 3rd year
Baseline between TSX-1and TDX-1 only 150m
Different geometry -> Change in exclusion zones -> Change in the Phase of Libration by 180o (to transmit with both satellites)
Larger HoA -> smaller baselines: Vertical dist. > 250 m Horizontal dist. > 120 m Minimum baseline: 100 m
Cross Track [m]R
adia
l[m]
ϕ = 20o
ϕ = 200o
Phase of libration: relative ascending node – relative perigee
Slide 20 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Formation Flying Configuration
Phase of libration: relative ascending node – relative perigeeVertical dist = 300 mHorizontal dist = 230 m
ϕ = 200oϕ = 20o
Slide 21 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
Different geometry -> Change in exclusion zones -> Change in the Phase of Libration by 180o (to transmit with both satellites)
Larger HoA -> smaller baselines: Vertical dist. > 250 m Horizontal dist. > 120 m Minimum baseline: 100 m
Cross Track [m]R
adia
l[m]
ϕ = 20o
ϕ = 200o
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Outline
Overview about TanDEM-X Mission
TanDEM-X Global DEM Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year
AntarcticaDifficult Terrain
Conclusions
Slide 22 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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TanDEM-X Global DEM Acquisition Plan
2010
Commissioningphase
2011
1st global coverage
2012 2013
2nd globalcoverage
Additional Acquisitions & Special Science
2014
2013
1st Antarcticahigher HoA
2014
Difficult terrain X 2 2nd Antarcticalower HoA
Science
May August April July
Slide 23 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Conclusions
The TanDEM-X mission will deliver a global DEM with unprecedented accuracyStable operations in close formation1st global coverage completed in March 2012, 2nd global coverage in April 2013Antarctica acquisitions in Left-Looking mode in May-June 2013Difficult terrain acquisitions from August 2013
Mountainous regions - shadow and layover effects => different viewing geometryDeserts: low SNR => steeper incidence angles
Slide 24 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Thank you for your attention!
Slide 25 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
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Slide 26 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era
Acquisitions for the 1st and 2nd Coverage