monostatic calibration of both tandem-x satellites€¦ · monostatic calibration of both tandem-x...

IGARSS 2010, Honolulu, 29th July

CALIBRATION

Monostatic Calibration of both TanDEM-X Satellites

Marco Schwerdt , Jaime Hueso Gonzalez,Markus Bachmann, Dirk Schrank,

Clemens Schulz, Björn Döring

IGARSS 2010, Honolulu 29.07.2010Slide 2

CALIBRATION

AntPoint

GeoCal

GS/SCCheckout

TSX-1 Launch

(15.06.2007)

RadiometricCalibration

Ant ModelVerification

TSX-1Commissioning Phase

5 Months

Summer 2007

TDX-1Comm. Phase

TDX-1 Launch

(21.06.2010)

5 Months

(Mono + Bi: 3+2)GeoCal

AntPoint

• • •

•••

ChannelImbalance

DRACampaigns

1 Month

Spring 2009


Antenna Model

Cross Talk


Ant ModelVerification

GeoCal

TSX-1Re-Calibration

1 Month

AntPoint

Summer 2009

≈

Ope

ratio

nal P

hase

≈

TSX-1 / TDX-1 In-Orbit Calibration Plan


CALIBRATION

TSX-1 Calibration


CALIBRATION

- Azimuth shift

- Instrument delay- Tropospheric effects

Time annotation of source packets

Range delay

Connection between SAR dataand geographic position on Earth surface

is calibrated

Geometric Calibration TSX-1

Internal Delay: 208.09 ns

-3-2,5

-2-1,5

-1-0,5

00,5

11,5

22,5

3

15 20 25 30 35 40 45 50 55Look Angle [deg]

Del

ta R

ange

[m]

Tests 2007 Mean 2007Tests 2009 Mean 2009

2m (requirement)

30 cm (1)(2 ns)

• Pixel localizationaccuracy (range)

6 corner reflectorsper pass8 beams

No trendsince 2 years 3.75 cm

(0.25 ns)• Residual offset

(in-flight OGC)

Near range Far range


CALIBRATION

Updates Improved ground

receiver position Re-adjustment between

star trackers

Pointing Determination in Azimuth TSX-1Antenna pointing determination

-30.00

-20.00

-10.00

0.00

10.00

20.00

30.00

17 22 27 32 37 42 47 52

Elevation look angle in deg

Dopp

ler i

n Hz

Pointing Calibration (2007)

Pointing Recalibration (2009)

Improvements 2007 2009 Measurement accuracy ≤ 7.9 Hz ≤ 2.6 Hz (1)

per pass < 1.0 mdeg < 0.33 mdeg

Mean doppler 16 Hz 5.9 Hz Residual pointing error 2 mdeg 0.74 mdeg

Notch patternswith different look angles4 ground receivers per pass

Near range Elevation look angle [degree] Far range

Freq

uenc

y sh

ift d

ue to

mis

poin

ting

[Hz]


CALIBRATION

PurposeDetect changes in the antenna front end and waveguides

120 km range

60 k

m a

zim

uth

Antenna Pattern Monitoring TSX-1

strip_003 strip_004 strip_005 strip_006

Quality parameters

*

max

µ

min

ScanSAR-mode: several beams measured during one passAcross an areaof 750 x 750 km²



CALIBRATION

Antenna Pattern Long Term Monitoring TSX-1

Shape deviationwithin

the main beamBeam-to-beamgain prediction

stable, no trendRequirement still fulfilled

Δ < ± 0.2dB


CALIBRATION

-57,6

-57,4

-57,2

-57

-56,8

-56,6

-56,4

-56,2

-56

-55,8

-55,6

10 15 20 25 30 35 40 45

Look Angle [deg]

Abs

Cal

Fac

tor[

dB]

strip_002strip_007strip_013

= -56.50 dB = 0.21 dB

= -56.76 dB = 0.24 dB

= -56.45 dB = 0.16 dB

strip_007

-57,6

-57,4

-57,2

-57

-56,8

-56,6

-56,4

-56,2

-56

-55,8

-55,6

Abs

Cal

Fac

tor[

dB]

near mid far

= -56.73 dB = 0.22 dB

= -56.65 dB = 0.17 dB

= -56.62 dB = 0.18 dB

= -56.67 dB = 0.18 dB

• Radiometric StabilityAbs. Cal Factor

2007 - 56.58 dB2009 - 56.43 dB

µ2009 = -56.53dB + 0.10dB (CR) = -56.43dB

µ ≤ ± 0.2dBwithin scene

Radiometric Calibration TSX-1

TerraSAR-Xis extremely stable

0.15dBover 2 years

µ ≤ ± 0.2dBwithin full

performancerange

Requirement 0.5 dB (1)over 6 months !

≤ ± 0.2dB• Antenna Model

CR: corner reflector

6 corner reflectorsacross the swath3 beams (low, mid, high inc.)


CALIBRATION

Calibration Tasks Performed in 2009 TSX-1

TerraSAR-X in Dual Receive Antenna (DRA) Mode2 instrument chains on receive (main and redundant)2 antenna halvesQuad-pol modeAlong track interferometry

DRA Campaigns Geometric calibration Antenna model verification Channel imbalance, phase Channel imbalance, amplitude radiometric calibration Cross talk

Ch. 2

Ch. 1


CALIBRATION

Channel Imbalance: Amplitude TSX-1

-0.18dB antenna gain Correction, V-pol on receive

max. offset0.44dB

Channelimbalance

0.26 dB

Abs. rad. accuracy during DRA campaigns

0.30 dB (1)

QuadPol Corner

-57,6

-57,4

-57,2

-57

-56,8

-56,6

-56,4

-56,2

-56

-55,8

-55,6

PolarisationA

bsC

al F

acto

r [dB

]

measured datamean

HH VV

= -56.46 dB = 0.09 dB

= -56.65 dB = 0.12 dB

QuadPol Transponder

-57,6

-57,4

-57,2

-57

-56,8

-56,6

-56,4

-56,2

-56

-55,8

-55,6

Polarisation

Abs

Cal

Fac

tor [

dB]

= -56.25 dB = 0.29 dB

= -56.49 dB = 0.33 dB

= -56.05 dB = 0.19 dB

= -56.40 dB = 0.39 dB

HH HV VH VV

(45° constellation)


CALIBRATION

Receiver forV-pol

Strip_013, des, Inc. 43.7° (16-04-2007)

One-Way Cross Polar Isolation TSX-1

Ground receivers aligned for V-pol1-way azimuth pattern measured per pass

H

V

Cross talk

Requirement ≥ 24dB (1-way, StripMap)

1-way cross polar isolation(on transmit)

> 34dB


CALIBRATION

TerraSAR-X Calibration Tasks Performed in 2009TerraSAR-X Calibration Team

27 DLR colleagues

DRA modecalibration

Radiometric stability0.15 dB (over 2 years)

Absolute radiometric accuracy0.39 dB (StripMap)

0.46 dB (DRA Quad-pol)

Channel imbalance0.26 dB / < 3 deg

Cross talk< - 24.9 dB

213 acquisitions171 over rainforest

42 cal-field (306 targets)

Re-calibration2 years after launch

CALIBRATION

TerraSAR-X is stable withoutstanding performancePointing accuracy

< 1 mdeg (azimuth)< 4 mdeg (elevation)

Pixel localization accuracy31 cm (range)

54 cm (azimuth)

Slide 12


CALIBRATION

TDX-1 Calibration


CALIBRATION

2.5 months (summer 2010)1. Geometric calibration2. Antenna pointing3. Antenna model4. Radiometric calibration

StripMap and ScanSAR

Cal test sites* Rainforest: distributed field* South Germany: 30 calibration sites

from which 17 are permanently installed corner reflectors

TanDEM-X calibration team32 DLR colleagues

Around 60 calibration campaignswith reference point targets:transponders and corners

More than 1000 datatakeswill be analyzed

TDX-1 Monostatic Calibration Strategy


CALIBRATION

D01x

D02x D03 x

D04x

D05x

D06x

D07x

D24-D30

x xx

xx

xx

D08

x D09x D10

xD12

xD14

x

D17x

D18x

D19x

D20x

D22 x

D11x

D13x D15

x

D16x

D21x D23

x

40km

120km

S007S007

Calibration Field in South Germany near by Oberpfaffenhofen

Munich


CALIBRATION

First Results: Chirp Comparison of TDX-1 – TSX-1

imagefrequencies

chirp

TSX-1TDX-1

Receive pulses, BW = 150MHz, UP-chirp, pulse length = 32µs

important forbistatic operationSimilar spectrograms


CALIBRATION

First results TDX-1: TRM Characterization – PN Gating

blue: measured in flight coldred: measured in flight hotblack: on ground characterization

Receive

Phas

e [d

egre

es]

Am

plitu

de [d

B]

TransmitPh

ase

[deg

rees

]A

mpl

itude

[dB

]

Warm instrument stability


CALIBRATION

First Results TDX-1: Antenna Pattern over Rainforest

Within requirements




CALIBRATION

First Results TDX-1: Antenna Pattern by Ground Receivers

Ground Receiver

PositionVector

Transmit pattern only

Relative accuracy< ± 0.1dB

Measurements confirmsimulated reference patternWithin requirements


CALIBRATION

First Sequential Ground Receiver Acquisition

3s azimuth separation ≈ 20 km

Direct measurement of the satellite separation in along track Pursuit monostatic phase

1st absolute comparative measurement of transmitted power <0.5dB difference TDX-1 – TSX-1

RX


CALIBRATION

Questions?

THE END

TSX-1 DLR logo experiment: Oberpfaffenhofen, Bayern, Germany (19th June 2008)

monostatic calibration of both tandem-x satellites€¦ · monostatic calibration of both tandem-x...

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