DTED-3

Feasibility Analysis of Pol-InSAR Applications 

with a TerraSAR-X Tandem Mission 

Alberto Moreira, Gerhard Krieger, Irena Hajnsek, Hauke Fiedler, Kostas Papathanassiou, 

David Hounam und Marian Werner 

German Aerospace Center (DLR) 

Microwaves and Radar Institute (HR) 

Postfach 1116 

82230 Weßling, Germany 

Alberto.Moreira@dlr.de 

Jan. 2005 

Datum: German 30.09.2004 Aerospace Center SAR-Strategiediskussion, RADAR 2004 - slide Folie 11 Institut für Hochfrequenztechnik Microwaves und Radarsysteme 

and Radar Institute

Response to DLR Call 

for Proposals for the next 

National Earth Observation Mission 

Datum: 30.09.2004 SAR-Strategiediskussion, Folie 2 

Institut für Hochfrequenztechnik und Radarsysteme

Spatial 

Resolution 

Interferometry with 

TanDEM-X 

Absolute 

Vertical 

Accuracy 

(90%) 

Relative 

Vertical 

Accuracy 

(90%) 

Absolute 

Horizontal 

Accuracy 

(90% circ.) 

Relative 

Horizontal 

Accuracy 

(90% circ.) 

DTED-1 90m x 90m < 16 m < 10 m < 60 m < 45 m 

DTED-2 30m x 30m < 16 m < 10 m < 20 m < 15 m 

DTED-3 

(HRTI-3) 

10m x 10m < 10 m 

Other Other product specifications (e.g. (e.g. 

DTED-4) will will be be considered during during 

phase phase A with with respect to to users users 

requirements 

< 2 m 

(4m,slope>20 %) 

< 10 m < 3 m 

SRTM / X-SAR E-SAR 

100 150 

DTED-2 DTED-3 



System and Mission Heritage 

X-SAR SAR SRTM 

DESA TOPAS 

CHAMP GRACE 

TerraSAR-X 

TerraSAR 

TanDEM-X 

TanDEM 



2SAT Pendulum 

Interferometry with TanDEM-X 

horizontal 

baseline 

Digital Elevation Model (DEM) 

from SRTM Mission 

vertical 

baseline 

2SAT Helix 

horizontal 

baseline 

Single-Pass Cross-Track Interferometry with TerraSAR-X Tandem: 

• no temporal surface decorrelation (as opposed to repeat-pass interferometry) 

• almost no atmospheric distortions (as opposed to repeat-pass interferometry) 

• large interferometric baselines 



Orbit Configurations I 



Two-Satellite Pendulum 

Flight direction 



Orbit Configuration II 



Two-Satellite Helix 

Flight direction 





v/PRF 

Three interferograms with 

two “effective baselines”: 

Bistatic Mode with 

Alternating Transmitters 

B monostatic = 2 • B bistatic 

SAT 1 

SAT 2 

+ good height accuracy 

(use large monostatic 

baseline) 

+ improved phase 

unwrapping 

(use smaller bistatic 

baselines) 

+ phase synchronization 

possible 

– requires increased PRF 

(as in in polarimetric mode) 

∂ϕ ∂ϕ 

= 2 

⋅ 

∂h 

∂h 

monostatic 

bistatic 



Parameter 

Wavelength 

Chirp Bandwidth 

Peak Transmit Power 

Duty Cycle 

Noise Figure 

Atmospheric Losses 

Antenna Size (Tx , Rx) 

PRF 

Processed Bandwidth 

Co-Registration Accuracy 

Quantization 

Sigma Nought Model 

(90% occurence levels) 

Effective Baseline 

Along-Track 

Displacement 

Swath Width 

Post Spacing 

Value 

0.031 m 

100 MHz 

2260 W 

18 % 

4.5 dB 

0.5 dB 

4.8 m x 0.7 m 

3500 Hz 

2300 Hz 

1/10 pixel 

3 bit (BAQ) 

Ulaby (X-Band, 

HH, Soil) 

1 km 

1 km 

30 km 

12 m x 12 m 

Interferometric 

Performance Estimation 

Relative Height Accuracy 



Scientific Areas 

Applications derived from across-track interferometry 

– Land Environment Topographic Topographic Mapping, Mapping, Cartography, Cartography, Urban Urban 

Areas, Areas, Disaster Disaster and and Crisis Crisis Management, 

Management, 

Navigation, Navigation, Archaeology, Archaeology, Change Change Detection Detection 

– Hydrology/Glaciology Ice Ice and and Snow, Snow, Wetlands, Wetlands, Morphology, Morphology, Flooding Flooding 

– Renewable Resources Land Land use use mapping, mapping, agriculture, agriculture, forestry forestry and and 

grassland grassland 

– Oceanography Wind Wind and and Waves, Waves, Ocean Ocean Dynamics, Dynamics, 

Ship Ship Detection, Detection, Bathymetry 

Bathymetry 

– Geology/Hazards Geological Geological mapping, mapping, Earthquake Earthquake /Tectonics, /Tectonics, 

Volcanoes, Volcanoes, Landslides 

Landslides 



Scientific Areas 

Applications with Along-Track Interferometry 

– Oceanography Ocean Ocean currents, currents, coastal coastal zone zone mapping mapping 

– Traffic Traffic Traffic flow flow monitoring monitoring 

– Glaciology Ice Ice flow flow monitoring monitoring 

New Techniques 

– Pol-InSAR 

– Digital beamforming 

– Multi-Angle Observations 

–Bi-static Processing 

–Super Resolution 

–Formation Flying 



Single Pass 

Polarimetric SAR Interferometry 

Pol-InSAR Natural Scatterers 

Observables 

3 Interferometric 

Coherences 

3 Interferometric 

Phases 

for one baseline and three 

polarisation states 

II Step: Model 

and Validation 

Inversion 

Coherent 

Scattering 

Model 

Forest 

Parameters 

Surface 

Parameters 

Agricultural 

Parameters 

Land Ice 

Parameters 



Polarimetric Interferometric: 

Performance Estimation 

ground-tovolume 

range 

µ min 

µ max 


Institut für Hochfrequenztechnik und Radarsysteme 

∆ϕ

Wheat (h=40cm, LAI=1.0, 30 m x 30 m) 

B = 500 m B = 1000 m B = 2000 m 

B = 4000 m B = 6000 m B = 8000 m 



Wheat (h=70cm, LAI=3.5, 30 m x 30 m) 

B = 500 m B = 1000 m B = 2000 m 

B = 4000 m B = 6000 m B = 8000 m 



Sun Flower (h=60cm, LAI=1.0, 30 m x 30 m) 

B = 500 m B = 1000 m B = 2000 m 

B = 4000 m B = 6000 m B = 8000 m 



Sun Flower (h=120cm, LAI=4.1, 30 m x 30 m) 

B = 500 m B = 1000 m B = 2000 m 

B = 4000 m B = 6000 m B = 8000 m 

ambiguous 



TanDEM-X Phase A 

Main challenges to to be be investigated in in Phase A: A: 

••PRF PRF and and Phase Synchronisation (design upgrade) 

••Precise Precise baseline determination using differential GPS 

and and phase measurements 

••Close Close formation flying capability 

••Bi-static Bi-static and and interferometric data data processing (DTED-3) 

••Spotlight Spotlight SAR interferometry 

••Interferometric Interferometric calibration (Ocean data data takes, tie tie points) 

••Scientific Scientific applications and and opportunities 



•• DEM-based applications (DTED-3): 

--land land environment, hydrology, 

geology, etc. etc. 

•• polarimetric SAR SAR interferometry 

•• along-track interferometry 

(e.g. (e.g. mapping of of ocean ocean currents, 

moving target target indication) 

•• super-resolution in in azimuth and and 

range range 

•• Digital Digital beam-forming with with 4 

phase phase centers 

•• multi-angle bistatic observations 

•• bi-static SAR SAR polarimetry 

•• stereogrammetric applications 

•• Formation flying 

flying 

Scientific Opportunities

DTED-3

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