new first topsar image and interferometry results with...

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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

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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

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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.

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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

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TerraSAR-X TOPSAR analysis

Ø A DTAR variation and scalloping of less than 1 dB is expected in

a typical TerraSAR-X TOPSAR configuration

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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

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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

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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

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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

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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

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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

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Challans: TOPSAR image

Time acquisition: July 9th, 2007 at 6.26 am

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Challans: ScanSAR image

Time acquisition: September 2nd, 2007 at 6.26 am

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First TOPSAR Interferometry results

with TerraSAR-X

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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

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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.

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Uyuni salt lake: TOPSAR coherence image

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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

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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

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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

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Thanks for your attention