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Folie 1
A. Meta - 29.11.2007
First TOPSAR image and interferometry results with
TerraSAR-X
A. Meta, P. Prats, U. Steinbrecher, R. Scheiber, J. Mittermayer
DLR – Microwaves and Radar Institute
Folie 2Microwaves and Radar Inst itute
Ø Introduction
Ø TOPSAR acquisition mode
Ø First TerraSAR-X TOPSAR images
Ø First TerraSAR-X TOPSAR interferometric fringe
results
Ø Conclusions and future work
Outline
Folie 3Microwaves and Radar Inst itute
Introduction
Ø TOPSAR is a new acquisition mode proposed by E. Attema (ESA-
ESTEC) and F. Rocca (POLIMI)
Ø Developed by POLIMI 1
Ø TOPSAR requires a fast rotation of the azimuth antenna pattern
Ø it aims at achieving the same coverage and resolution as
ScanSAR, but with a nearly uniform SNR and DTAR
Ø It is going to be the operational mode for Sentinel-1
Interferometric Wide Swath (IWS) mode
Ø It is being successfully demonstrated with TerraSAR-X for the first
time within the framework of an ESA project
1) F. D. Zan and A. M. Guarnieri, “TOPSAR: terrain observation by progressive scan“, IEEE Trans. Geosci.
Remote Sensing, vol. 44, no. 9, pp. 2352 -2360, Sept. 2006.
Folie 4Microwaves and Radar Inst itute
TOPSAR acquisition mode
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TOPSAR acquisition mode
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Antenna array effects
Boresight caseNormalized angle of the
steering angle equal to 0.2
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Ø The azimuth array antenna pattern is amplitude
weighted by the single element pattern
Ø When the array pattern is being steered, the effect of
the grating lobes is increasing.
Ø A small residual scalloping effect can be introduced
Ø However, it is much smaller than the equivalent
ScanSAR case and has a lower frequency due to
extended burst image area
Antenna array effects
Folie 8Microwaves and Radar Inst itute
TerraSAR-X TOPSAR analysis
Ø A DTAR variation and scalloping of less than 1 dB is expected in
a typical TerraSAR-X TOPSAR configuration
Folie 9Microwaves and Radar Inst itute
Inverse TOPSAR
Nominal TOPSAR Inverse TOPSAR
0 0
0
21 1
i
i
k R k R vk k
v v R
! !! !+ = " # = +
Ø The timeline equation are the same for TOPSAR and inverse TOPSAR
Ø Steering rate higher in inverse TOPSAR, therefore higher scalloping
and DTAR variation to be expected
Folie 10Microwaves and Radar Inst itute
First TOPSAR images with TerraSAR-X
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TerraSAR-X TOPSAR configuration
Ø four subswaths
Ø ~80 km swath coverage
Ø 16 m azimuth resolution
± 0.75 degMaximum steering angle
514 kmHeight
7608 m/sSatellite velocity
0.33 degOne-way azimuth beamwidth
(3 dB)
12TR modules in along-track
4.8 mAlong-track antenna length
9.65 GHzCarrier frequency
TerraSAR-X parameters
Folie 12Microwaves and Radar Inst itute
TerraSAR-X TOPSAR acquisition example
9464.99467.99469.19471.4Burst image length – [m]
1234132611361220Number of Pulses per Burst – [ ]
0.49770.5060.5130.522Maximum steering angle - [deg]
454.79455.01455.13455.31Target Doppler Bandwidth – [Hz]
0.3050.3030.3010.300Burst Time – [s]
-24.99-25.31-23.46-25.03DTAR – [dB]
3.2513.3373.4043.479Steering angle rate – [deg/s]
0.3290.3290.3290.329Integration beamwidth – [deg]
Calculated parameters
4035436837614063PRF – [Hz]
6960696669706976Ground velocity – [m/s]
632.5616.5604.6591.8Slant middle range – [km]
34.08632.07530.42628.464Mean look angle - [deg]
Input parameters
SS 4SS 3SS 2SS 1
Folie 13Microwaves and Radar Inst itute
Vendome: inverse TOPSAR image
Ø Scene size: 84 km in
azimuth and 72 in slant
range
Ø 8 bursts
Ø Antenna steering from
+0.71 deg to -0.71 deg
Ø Burst image steering from
+0.67 deg to -0.67 deg
Ø Small scalloping effect
visible
Ø No scalloping correction
applied
Ø Data Take acquired on
June 29th, 2007, only two
weeks after the TerraSAR-
X launch
Folie 14Microwaves and Radar Inst itute
Neuville: TOPSAR image
Ø Scene size: 90 km in
azimuth and 75 in slant
range
Ø 9 bursts
Ø Antenna steering from
+0.55 deg to -0.55 deg
Ø Burst image steering from
+0.44 deg to -0.44 deg
Ø Difficult to see scalloping
effects
Ø No scalloping correction
applied
Folie 15Microwaves and Radar Inst itute
Inverse TOPSAR
azimuth profile example
~0.8 dB scalloping
Nominal TOPSAR
azimuth profile example
~0.4 dB scalloping
Azimuth profiles
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Challans: Google image
Folie 17Microwaves and Radar Inst itute
Challans: TOPSAR image
Time acquisition: July 9th, 2007 at 6.26 am
Folie 18Microwaves and Radar Inst itute
Challans: ScanSAR image
Time acquisition: September 2nd, 2007 at 6.26 am
Folie 19Microwaves and Radar Inst itute
First TOPSAR Interferometry results
with TerraSAR-X
Folie 20Microwaves and Radar Inst itute
TerraSAR-X TOPSAR interferometry
A squint error translates into a Doppler shift
The TerraSAR-X characteristics:
Ø Along-track position accuracy is within ~50 m (0.005 deg at 620
km)
Maximum Doppler shift of approximately 40 Hz
For a processed Doppler bandwidth of 455 Hz (16 m res.), a
maximum interferometric resolution loss of less than 9% is
expected due to band filtering.
2
shift
vf !"
#=!"
Accurate coregistration is required due to high Doppler centroids at
the edges of the burst images.
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Uyuni salt lake
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Uyuni salt lake
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Uyuni salt lake: TOPSAR master image
Ø Scene size: 110 km in
azimuth and 74 in slant
range
Ø 8 bursts
Ø Look angle is varying from
32.9 degree to 37.9 degree
Folie 24Microwaves and Radar Inst itute
Uyuni salt lake: TOPSAR slave image
Ø Same configuration as the
master data take
acquisition
Ø Coarse misalignment of 70
pixel in range and 3 in
azimuth
Ø Along-track misalignment
around 22 m.
Folie 25Microwaves and Radar Inst itute
Uyuni salt lake: TOPSAR coherence image
Folie 26Microwaves and Radar Inst itute
Uyuni salt lake: TOPSAR interferogram
Ø The estimated range
frequency is linearly
decreasing with increasing
range and with along-track
position,
Ø estimated perpendicular
baseline varying from 67 to
38 meter
Ø The resulting ambiguity
height is varying from
approximately 92 to 173
meter.
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Uyuni salt lake: TOPSAR final interferogram
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Unwrapped phase
Folie 29Microwaves and Radar Inst itute
Doppler centroid variation effects
( )2
0
_
41 1
2
DC
rg err mis
f rr
v
!"#
!
$ %$ %& '= ( ) )& '& '* +* +
_ 2az err DCf t! "= #
0.1 pixel azimuth misregistration
Negligible effect
Very important
Folie 30Microwaves and Radar Inst itute
Ø Calibration of the TOPSAR interferometry phase and
quantitative analysis
Ø Processing of TerraSAR-X data takes for Sentinel-1 simulations
in terms of coverage, steering angle, scalloping
Ø Final results will be used for suggestions for the TOPSAR IWS
of the ESA Sentinel-1 sensor
Next steps
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Conclusions
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Ø TerraSAR-X TOPSAR data takes have been successfully
generate, commanded and executed
Ø First TOPSAR images have been produced with the
experimental processor developed at DLR
Ø First TOPSAR interferometric fringe have been successfully
generated over the Uyuni salt lake
Ø Unique validation approach by joining the knowledge and
expertise of TerraSAR-X SEC, processing and airborne groups
at the DLR – Microwaves and Radar Institute
Conclusions
Folie 33Microwaves and Radar Inst itute
Thanks for your attention
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