Techniques for High Accuracy Relative and Absolute Localization of TerraSAR-X / TanDEM-X Data U....

Techniques for High Accuracy Relative and

Absolute Localization of TerraSAR-X /

TanDEM-X Data

U. Balss, M. Eineder, T. Fritz, H. Breit, and C. MinetGerman Aerospace Center (DLR),

Remote Sensing Technology Institute (IMF)

Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum

Folie 2

2Institut für Methodik der

Fernerkundung

Outline

Introduction

Measurement MethodConsideration of Continental Drift

Particulars of Bistatic Acquisition Geometry

Measurement Results ofAbsolute Localization Accuracy (TerraSAR-X)

Relative Localization Accuracy (TanDEM-X)

Conclusions


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Fernerkundung

Introduction

TSX-1 (launched June 2007) and TDX-1 (launched June 2010) constitute first bistatic SAR system in space.

One satellite transmits radar pulses.

Both satellites receive the echoes.

High geometric accuracy requires consideration of

signal propagation effects

geodynamic effects

in geolocation of ground targets.

passive channel: Geolocation is additionally complicated by bistatic acquisition geometry


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Measurement Method

6 Corner Reflectors (CR) at Oberpfaffenhofen Test SiteComparison of

measured radar positionstheir expected values

Expected values are based onprecise GPS measurements of CR positionsorbit interpolation of satellites’ positions

The following effects have to be taken into account:additional signal delays(caused by electrons in ionosphere andwater vapor in atmosphere)solid earth tidescontinental drift


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Continental Drift and Geodetic Coordinate Systems

*

TSX-1 / TDX-1 orbit inITRS-2005/08 coordinates

*

GPS position of CR in tectonic platefixed system (e.g. ETRS89)

misinterpretation ofGPS coordinates

offset between expected and true CR position(e.g. approx. 60 cm if ETRS89 is taken for ITRF-2005)


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Effect of Continental Drift on Radar Coordinates(e.g. corner reflector CR moved to northeast)

expectedposition

of CR

trueposition

of CR

flight path

continentaldrift

azimuth

range

ascending orbit(right looking):

CR occurs more inlate azimuthandfar rangethan expected

WS

NE

height

t1

t2>t1


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Effect of Continental Drift on Radar Coordinates(e.g. corner reflector CR moved to northeast)

expectedposition

of CR

trueposition

of CR

flight path

continentaldrift

azimuth

range

descending orbit(right looking):

CR occurs more inearly azimuthandnear rangethan expected

WS

NE

height

t2<t1

t1


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Effect of a Coordinate System Mismatch

Wrong: ETRS89 coordinates are misinterpreted as ITRS-2005

Correct: ETRS89 coordinates are transformed to ITRS-2005 system

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

range offset [m]az

imu

th o

ffse

t [m

]

ascending

descending

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

range offset [m]

azim

uth

off

set

[m

]

ascending

descending


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Bistatic Acquisition Geometry of TanDEM-X(Passive Imaging Channel)

tRTx tRRx

tRttRtR RxTx 2

1

c

tRt

2

bistatic range

depends on signal travel time

which again dependson bistatic range


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Computation of Bistatic Closest Approach

20~R

t~t

AT

2R

iteration step (n=0, 1, 2, …)

estRx RtRtR 0

tR

c

tRtRtR Rx

n

Txn 2

2

11

initialization

2) Coordinate of hyperbola apexresults by nested intervals.

1) Recursive computation of bistatic range for given slow time t:


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Bistatic Acquisition Geometry of TanDEM-X(Active Imaging Channel)

Satellite moves during signal travel time.

Satellite position differs between instants of pulse transmission and echo reception.

Thus, even this acquisition geometry is strictly speaking bistatic.

Results of monostatic and bistatic computation scheme differ by some tenth of a millimeter.

tRTx tRRx


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Absolute Pixel Localization Accuracy of TSX-1(Based on TSX-1 Calibration Datatakes 2007/09)

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

range offset [m]

azim

uth

off

set

[m]

100 MHz150 MHz300 MHz

L1B products createdbefore 2011-07-15:

bandwidth dependent range offset:100 MHz : -33 cm150 MHz : -14 cm300 MHz : +12 cm

azimuth offset: +8 cm

Meanwhile bandwidth dependency is solved by code change in SAR processor and instrument is recalibrated.


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Absolute Localization Accuracy of TSX-1(Reprocessed by Actual SAR Processor Version)

σazimuth = 6.3 cmσrange = 3.8 cm

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

range offset [m]

azim

uth

off

set

[m]

100 MHz150 MHz300 MHz

The following offsetsare subtracted:

azimuth offset: +8 cmrange offset : -29 cm


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Absolute Localization Accuracy of TSX-1 and TDX-1 (Based on Calibration Datatakes 2010)

TDX-1σazimuth = 5.5 cmσrange = 3.5 cm

TSX-1σazimuth = 5.3 cmσrange = 3.5 cm

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

range offset [m]

azim

uth

off

set

[m

]

HH 100 MHzHH 150 MHzVV 100 MHzVV 150 MHz

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

range offset [m]

azim

uth

off

set

[m

]

HH 100 MHz

HH 150 MHz

VV 100 MHz

VV 150 MHz


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Relative Localization Accuracy of Bistatic TanDEM-X Acquisitions

different scaling of axesazimuth: -100 … +60 mmrange : -10 … +6 mm

!

mean value:mazimuth = -18 mmmrange = -2.1 mm

standard deviation:over all acquisitions:σazimuth = 40 mmσrange = 4.4 mmwithin an acquisition:σazimuth = 16 mmσrange = 1.0 mm

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

-0.010 -0.008 -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006

range offset [m]

azi

mu

th o

ffs

et [

m]

TSX-1 active

TDX-1 active


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Conclusions

Geolocation of ground targets has to accurately consider signal propagation and geodynamic effects.

Taking these effects into account, we reveal a much better absolute pixel localization accuracy of TSX-1 / TDX-1, than previous studies.

The increased measurement accuracy also helped us to identify and solve a small systematic effect in SAR processing.

TerraSAR-X: Absolute pixel localization accuracy in the order of magnitude of just few centimeters.

TanDEM-X: Relative pixel localization accuracy in range direction even at sub-centimeter level.

Thank you for your attention!

Date post:	28-Mar-2015
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Techniques for High Accuracy Relative and Absolute Localization of TerraSAR-X / TanDEM-X Data U....

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