irena.hajnsek@dlr.de 26-Jan-2009

Polarisation Capabilities and Status of TerraSAR-X

Irena Hajnsek, Josef Mittermayer, Stefan Buckreuss, Kostas Papathanassiou German Aerospace CenterMicrowaves and Radar Institute

Slide 2

TerraSAR-X Satellite

Solar Generator

X-Band Radar Antenna384 Transmit/Receive Modules

X-Band Downlink AntennaData Rate: 300 MBit/sec

256 Gbit Solid State Mass Memory

S-Band TM/TC Antenna

Thrusters

Wet mass: 1209 kgOrbit average power: 800 W Size: 5 m height × 2.4 m diameter

Slide 3

TerraSAR-X Satellite Key FeaturesHigh resolution in SpotLight mode

Possibility of large area coverage by utilizing ScanSAR mode

Multi-polarization capability

Left Looking Mode (roll maneuver of S/C)

Dual Receive Antenna (DRA) Mode (ATI, MTI, Quad. Pol.)

300 MHz transmit bandwidth (1 m range resolution)

Reference orbit with ±250 m orbit tube (repeated acquisitions, interferometry, etc.)

Total Zero Doppler Steering

Secure operation by encryption of commands and data downlink

Prepared for TanDEM-X operation (synchronization)

Slide 4

Munich Oktoberfest Site

• Januar – Juni 2008 • 31.7. – 22.8.2008 • DifferenzInstitut für Methodik

der Fernerkundung

Slide 5

Data Quality

AchievementsImprovementsTrendsPlans…

Slide 6

Calibration: Results of the Commissioning PhaseGoal: SAR product verification and release of the basic products

• Verification of format, annotation and content passed

• Updated basic product specificationImprovements w.r.t. initial version as for example (Stripmap)

o absolute radiometric accuracy: 1.1 dB 0.6 dB

o relative radiometric accuracy 0.68 dB 0.31 dB

o spotlight mode (azimuth) resolution 2.2 m 1.7 m

o pixel localization accuracy 2.0 m 0.3 m in range2.0 m 0.53 m in azimuth

o side lobe ratio improved by approx. 10 dB**(at the cost of a reduction of the slant range resolution of 9 % from 1.1 m to 1.2 m)

Slide 7

DubaiStripmapVV-pol.

• 26. Juni 2007 • 7. April 2008• Difference

Slide 8

High Resolution Spotlight Image of Anak KrakatauImproperly amplified DC-part of SAR image

=> range stripes

Slide 9

High Resolution Spotlight Image of Anak KrakatauSpectral thresholding eliminates range stripes (improved replica implementation)

Slide 10

Noise Correction in TerraSAR-X Processor TMSP

noise pattern in low backscatterareas typical for ScanSAR

results from azimuth and elevation antenna pattern correction for the individual bursts

signal is perfectly calibrated but additional noise power is inhomogeneously distributed

multiple superposition of statistical signal and noise distributions

impairs some applications (e.g. ship detection)

ScanSAR Sydney, Australia (2008-01-30)

Slide 11

noise corrected product

New SAR processor softwareis activated since Dec 1st, 2008

Noise Correction in TerraSAR-X Processor TMSP

Slide 12

Instrument Stability:• I/Q Statistic stable, no Trend• TRM Monitoring (rel. ampl/phase): < 0.23 dB / < 2.0 deg (1σ)

Antenna Pattern Monitoring• Shape within Main Beam• Gain-Offset between different beams

Radiometric Stability• Requirement over 6 months 0.5 dB (1σ) (requirement)

• Observed over 1 year0.14 dB

Calibration: Resumé after 1 Year of Operations

≤ ±0.2 dB (peak to peak)

No significant variation has been observed since launch!

Slide 13

Experimental Modesof TerraSAR-X

Slide 14

TOPSAR Acquisition ModeTOPSAR is a modified ScanSARmode:

Ambiguity Reduction„Scalloping“ Reduction

TOPSAR Interferogram

Slide 15

range

azim

uth

Conducted on 5th of November 2007TX with TerraSAR-X, RX with F-SARImportant preparation for TanDEM-X

Clock synchronizationIn-orbit-phase-noise investigationsPerformance verification of bistaticprocessing and imaging techniques

Bistatic Imaging

Slide 16

Principle

• For transmit the full antenna is used

• For receive the antenna is ‚electrically‘ divided into two sections inazimuth direction two independent receive channels are available

New Experimental Modes

• Along-Track Interferometry (ATI)(Moving Target Indication, Widespread Traffic Control, Ocean Current Measurement)

• Quad polarization(Sea/Ice, Snow Cover, Urban Environment)

Transmit Receive

Dual Receive Antenna Mode (DRA Mode)

TX: V H V H …RX1: V V V V …RX2: H H H H …CH1: VV HV VV HV …CH2: VH HH VH HH …

Quadpol switching scheme

Slide 17

Polarization ModesH H H H

H H H H

Transmit

Receive

Single Polarization• 1 polarization

channel, {HH, VV}• stripmap, spotlight,

ScanSARDual Polarization• 2 polarization

channels, {HH/VV, HH/HV, VV/VH}

• stripmap, spotlight• coherent pol. phase• smaller elevation beam

H H H HTransmit

ReceiveV

H H H H

V V VH H H H

Quad Polarization• All 4 pol. channels• Stripmap• coherent pol. Phase• smaller elevation beam• Experimental product

H H H HTransmit

ReceiveV

V V V V

V V V

H H H HH H H H

V V V V

Twin Polarization• 2 polarization

channels, {HH/VV, HH/HV, VV/HV}

• stripmap• incoherent pol. phase• full elevation beam

H HTransmit

ReceiveV

H

V VHH

Slide 18

First TerraSAR-X Quadpol Image!

Workuta, Russia StripmapJune 23, 2008red: HH-VVgreen: (HV+VH)/2

blue: HH+VV

Slide 19

Polarimetric Analysis (dual pol HHVV) @ X-Band

HHVV Coherence(amplitude)

RGB (hh+vv,hh,hh-vv)

Slide 20

Polarimetric Analysis (dual pol HHVV)

HHVV Coherence(phase)

RGB (hh+vv,hh,hh-vv)

Slide 21

Polarimetric Analysis (dual pol HHVV vs quad pol)RGB

(hh+vv,hh,hh-vv)

RGB (hh+vv,2hv,hh-vv)

Slide 22

Dual Receive Mode Implementation (1)

Decision to activate the redundant receive channel in March‘08

Commanding of DRA mode was proved

Instrument is capable to execute the DRA mode

SAR Workflow is running well

Manually(!) tuned quadpol product is available (June’08, IGARSS’08)

Identified problems:

Channel decoupling is problematic, on-ground characterization not sufficient

New command structure w.r.t. additional cal pulses to be developed

Commanding and processing to be iteratively optimized

Slide 23

Dual Receive Mode Implementation (2)

Work in progress:

Presently test data takes are carried out and evaluated

Review of results and final decision on way forward

Calibration campaign (3 cycles) in spring 2009 (tbc)

Final product release in summer 2009 (tbc)

Quota limitation for future acquisitions to be discussed

(Reliability calculation due to the use of redundancies)

Slide 24

Spacecraft and ground segment are fully operational

Image products (Spotlight, Stripmap, ScanSAR) are calibrated and released

Product quality within initial specification or better!

SAR instrument proved to be very stable

Demonstration of Repeat Pass Interferometry, Along Track Interferometry, persistent scatterer evaluation, TOPSAR, total zero Doppler steering

Demonstration of quadpol mode

The use of TerraSAR-X data was demonstrated for geo-scientific applications, oceanography and disaster monitoring during commissioning phase

Preparation of TanDEM-X mission gains priority…!

Status Summary