Techniques for High Accuracy Relative and Absolute Localization of TerraSAR-X / TanDEM-X Data U. Balss , M. Eineder, T. Fritz, H. Breit, and C. Minet German Aerospace Center (DLR), Remote Sensing Technology Institute (IMF)
Mar 28, 2015
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 3
3Institut für Methodik der
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 4
4Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 5
5Institut für Methodik der
Fernerkundung
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)
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 6
6Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 7
7Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 8
8Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 9
9Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 10
10Institut für Methodik der
Fernerkundung
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:
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 11
11Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 12
12Institut für Methodik der
Fernerkundung
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.
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 13
13Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 14
14Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 15
15Institut für Methodik der
Fernerkundung
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
Institut für Methodik der Fernerkundung bzw. Deutsches Fernerkundungsdatenzentrum
Folie 16
16Institut für Methodik der
Fernerkundung
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!