tandem-x: dem acquisition in the third year era...stable operations in close formation 1st global...

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

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

Outline


TanDEM-X Acquisition PlanCurrent Acquisition Status (First and Second Year)Acquisition Plan for the Third Year


Conclusions


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


Helix FormationSlide 5 www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era

Cross-Track Interferometry for DEM Acquisition

B

H

z

TanDEM-XφUnwrapping

DEM

Image1 Image 2

TerraSAR-X

Interferogram


Outline




Conclusions


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


Interferometric Coherence of 1st Year120000 scene (1 scene = 50x30 km2)

Mean land coherence: 91.8% higher than 0.6 (“Good”-Quality Flag: 87.6%)


Forest: Volume Decorrelation

Deserts: Low SNR

Solid Surface:High Coherence

Mountains:Shadow/Layover

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


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


Outline




Conclusions


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


Antarctica

Left-Looking acquisitions over a radius of 1300 km


Right-Looking acquisitions in the outer region

Outline




Conclusions


Difficult Terrain: Deserts and Mountainous Regionsto be acquired in the Third Year

- Shadow and Layover- Desert


Difficult Terrain: Mountainous Regions

Steep and rough surfaces=> Phase unwrapping errors=> HoA > 85 m required

Shadow and Layover effects


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


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)



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



Phase of libration: relative ascending node – relative perigeeVertical dist = 300 mHorizontal dist = 230 m

ϕ = 200oϕ = 20o


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

Outline




Conclusions


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


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


Thank you for your attention!


www.dlr.de , D. Borla Tridon: TanDEM-X DEM Acquisition in the Third Year Era

Acquisitions for the 1st and 2nd Coverage

tandem-x: dem acquisition in the third year era...stable operations in close formation 1st global...

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