5_IGARSS2011_HU.pdf

Blind Azimuth Phase Elimination for TerraSAR-X ScanSAR InterferometryAlex Zhe Hu, Linlin Ge and Xiaojing LiGeodesy and Earth Observing Systems Group (GEOS),School of Surveying and Spatial Information Systems,The University of New South Wales, Sydney, Australia

Email: [email protected]

mailto:[email protected]

Contents

• Introduction• Methodology• Results and Discussions• Concluding Remarks

Contents


Introduction• ScanSAR Mode

– Burst Mode– Imaging time < a synthetic aperture

ScanSAR Mode

Stripmap Mode

image originally from Infoterra: http://www.infoterra.de

http://www.infoterra.de/

Introduction• ScanSAR Mode

– Cover multiple swathes– Large range coverage

ScanSAR Mode

Stripmap Mode

image originally from Infoterra: http://www.infoterra.de

http://www.infoterra.de/

Introduction• ScanSAR Interferometry

– Cover multiple swathes– Large range coverage

– Global DEM– Large-scale Earthquakes

Introduction• ScanSAR Interferometry

ALOS PALSAR

EnviSATASAR RADARSAT TerraSAR-X

L-band C-band C-band X-band

250–350km 400km 300–500km 150km

100m 75–150m 50–100m up to 16m

Shimada 2007 Ortiz and Zebker 2007

Holzner and Bamler 2002 ?

Introduction• TerraSAR-X ScanSAR Interferometry

– Distortion and signal loss in azimuth direction after resampling

– Only SLC data available for the public

Introduction• TerraSAR-X ScanSAR Interferometry

– Distortion and signal loss in azimuth direction after resampling

– Only SLC data available for the public

– Blind Azimuth Phase Elimination

Contents


Methodology• Phase Estimation Strategy

– The simulated burst for compensation should have similar fringe patterns

Methodology• Brief workflow

Determination of the Compensation Factor

Coarse Initialisation of the Key Parameter

Refining of the Key Parameter

Elimination of the Azimuth Phase

( ) ( )2 00s expstrip dmj f w

Tτ ττ π τ τ −⎛ ⎞⎡ ⎤= − ⋅ ⎜ ⎟⎣ ⎦ ⎝ ⎠

( ) ( )20exp rect c

scan dmb

Ts j fT

ττ π τ τ⎛ ⎞−⎡ ⎤= − ⋅ ⎜ ⎟⎣ ⎦ ⎝ ⎠

Moving Direction (Azimuth)

Sensor Sensor

Target

Synthetic Aperture

Stripmap


Sensor Sensor

Target

Burst Time

ScanSAR

• Determination of the Compensation Factor

Methodology


Sensor Sensor

Target

Synthetic Aperture

Stripmap


Sensor Sensor

Target

Burst Time

ScanSAR


Methodology

( ) ( ) ( ) ( )0sincstrip strip ref dmc s s T f Tτ τ τ π τ τ= ∗ = ⋅ −⎡ ⎤⎣ ⎦

( ) ( ) ( ) ( ) ( ) ( ){ }2 20 0sinc expscan scan ref b dm b dm c cc s s T f T j f T Tτ τ τ π τ τ π τ τ⎡ ⎤= ∗ = ⋅ − ⋅ − − − −⎡ ⎤⎣ ⎦ ⎣ ⎦


Sensor Sensor

Target

Synthetic Aperture

Stripmap


Sensor Sensor

Target

Burst Time

ScanSAR

Methodology

( ) ( ) ( ) ( )0sincstrip strip ref dmc s s T f Tτ τ τ π τ τ= ∗ = ⋅ −⎡ ⎤⎣ ⎦

( ) ( ) ( ) ( ) ( ) ( ){ }2 20 0sinc expscan scan ref b dm b dm c cc s s T f T j f T Tτ τ τ π τ τ π τ τ⎡ ⎤= ∗ = ⋅ − ⋅ − − − −⎡ ⎤⎣ ⎦ ⎣ ⎦

( ) ( ){ }2exp dm cg j f Tτ π τ⎡ ⎤= −⎣ ⎦



Sensor Sensor

Target

Synthetic Aperture

Stripmap


Sensor Sensor

Target

Burst Time

ScanSAR

( ) ( )

Methodology

{ }2exp dm cg j f Tτ π τ⎡ ⎤= −⎣ ⎦

( ) ( ) ( ) ( ) ( ) ( )0sinc expscan scan ref b dm bc s s g T f T jτ τ τ τ π τ τ φ⎡ ⎤= ∗ ⋅ = ⋅ − ⋅⎡ ⎤⎣ ⎦⎣ ⎦


Methodology• Coarse Initialisation of the Key Parameter

– The compensation factor is a function of burst duration Tb

( ) ( ){ } ( ){ }2 2exp exp 2dm c dm s bg j f T j f T Tτ π τ π τ⎡ ⎤ ⎡ ⎤= − = − −⎣ ⎦ ⎣ ⎦


( ) ( ) ( ) ( ) ( ){ }( ) ( ) ( ){ }

1

1

scan scan ref scan ref

strip ref

c s s F F s F s

F a S W F s

τ τ τ τ τ

ω ω τ

−

−

⎡ ⎤= ∗ = ⋅⎡ ⎤⎣ ⎦ ⎣ ⎦

⎡ ⎤ ⎡ ⎤= ⋅ ∗ ⋅⎣ ⎦ ⎣ ⎦


– time difference between two peaks of sincfunction is determined by Tb

( ) ( ) ( ) ( ) ( ){ }( ) ( ) ( ){ }

1

1

scan scan ref scan ref

strip ref

c s s F F s F s

F a S W F s

τ τ τ τ τ

ω ω τ

−

−

⎡ ⎤= ∗ = ⋅⎡ ⎤⎣ ⎦ ⎣ ⎦

⎡ ⎤ ⎡ ⎤= ⋅ ∗ ⋅⎣ ⎦ ⎣ ⎦

( ) ( ){ } ( ){ } ( )11 sincscan ref strip bb

F F F c F s F S TaT

τ τ ω ω− ⎡ ⎤ ⎡ ⎤⋅ =⎡ ⎤⎣ ⎦ ⎣ ⎦ ⎣ ⎦


Methodology• Refining of the Key Parameter

– Iteratively approaching to the real value

Methodology• Comprehensive workflow

Burst N

Calculatinginitial burstduration Tb0

Generatingcompensation

Burst

Computingcorrelation

factor

compensationBurst

Correlationdecreasing?

IncreasingTb

Final compBurst

Y

N

Fittingcorrelation to find the peak

Contents


Information Master Image Slave Image

Acquisition Date 16 February 2010 27 February 2010

Acquisition Start Time 02:56:12 (UTC) 02:56:13 (UTC)

Acquisition Stop Time 02:56:30 (UTC) 02:56:31 (UTC)

Number of Swathes 4 (strip_04 – strip_07)

Number of Bursts 59 (strip_04 – strip_07) 61 (strip_04 – strip_07)

Central Latitude 28.785 ° 28.785 °

Central Longitude 47.514 ° 47.513°

Range Resolution 2.504 (metre) 2.503 (metre)

Azimuth Resolution 18.5 (metre) 18.5 (metre)

Results and Discussions

Original Bursts


Original Bursts

Compensation Phases


Original Bursts

Compensation Phases

Bursts after azimuth phase elimination


Resampled slave Burst-based interferogram


TerranSAR-X ScanSARInterferogram

ScanSAR Derived Height Value

-Pi Pi 0 300m


ScanSAR Derived DEM


Histogram of the difference


Height difference to SRTM DEM-50 50m

Contents


Concluding Remarks• Simplifying the TerraSAR-X ScanSAR

interferometry by making it Stripmap-like• Precise enough to remove the non-linear

azimuth phases• Providing a solution for TerraSAR-X

ScanSAR interferometry starts from SLC data

• Can also be applied to other advanced SAR system with non-linear azimuth phases, such as Spotlight

Acknowledgement:

The authors are grateful to Infoterra for providing the TerraSAR-X ScanSAR dataset on this research.

The first author also sincerely thanks GEOS and the Faculty of Engineering of UNSW for supporting his scholarship on his PhD study.

Education

5_IGARSS2011_HU.pdf