th1.l10.3: monostatic calibration of both tandem-x satellites

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 29.07.2010

Slide 2

CALIBRATION

AntPoint

GeoCal

GS/SCCheckout

TSX-1 Launch

(15.06.2007)

Radiometric

Calibration

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

DRACampaign

s1 Month

Spring 2009

RadiometricCalibration

Antenna Model

Cross Talk

RadiometricCalibration

Ant ModelVerification

GeoCal

TSX-1Re-

Calibration1 Month

AntPoint

Summer 2009

≈

Op

era

tio

na

l P

ha

se

≈

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


Slide 3

CALIBRATION

TSX-1 Calibration


Slide 4

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 55

Look Angle [deg]

Del

ta R

ang

e [m

]

Tests 2007 Mean 2007

Tests 2009 Mean 2009

2m (requirement)

30 cm (1)(2 ns)

• Pixel localizationaccuracy (range)

6 corner reflectorsper pass

8 beams

No trendsince 2 years 3.75 cm

(0.25 ns)• Residual offset

(in-flight OGC)

Near range Far range


Slide 5

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

Do

pp

ler

in H

z

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 angles

4 ground receivers per pass

Near range Elevation look angle [degree] Far range

Fre

qu

en

cy s

hift

du

e t

o m

isp

oin

ting

[H

z]


Slide 6

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 pass

Across an areaof 750 x 750 km²



Slide 7

CALIBRATION

Antenna Pattern Long Term Monitoring TSX-1

Shape deviationwithin

the main beam

Beam-to-beamgain prediction

stable, no trendRequirement still fulfilled

Δ < ± 0.2dB


Slide 8

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]

Ab

s C

al F

acto

r [d

B]

strip_002

strip_007

strip_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

Ab

s C

al F

ac

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 Stability

Abs. Cal Factor2007 - 56.58 dB

2009 - 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 swath

3 beams (low, mid, high inc.)


Slide 9

CALIBRATION

Calibration Tasks Performed in 2009 TSX-1

TerraSAR-X in Dual Receive Antenna (DRA) Mode

2 instrument chains on receive (main and redundant)

2 antenna halves

Quad-pol mode

Along track interferometry

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

Ch. 2

Ch. 1


Slide 10

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

Polarisation

Ab

sC

al

Fa

cto

r [d

B]

measured data

mean

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

Ab

sCal

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)


Slide 11

CALIBRATION

Receiver for

V-pol

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

One-Way Cross Polar Isolation TSX-1

Ground receivers aligned for V-pol

1-way azimuth pattern measured per pass

H

V

Cross talk

Requirement ≥ 24dB (1-way, StripMap)

1-way cross polar isolation (on transmit)

> 34dB


Slide 12

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 accuracy

0.39 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 with outstanding

performance

Pointing accuracy< 1 mdeg (azimuth)< 4 mdeg

(elevation)

Pixel localization accuracy

31 cm (range)54 cm (azimuth)

Slide 12


Slide 13

CALIBRATION

TDX-1 Calibration


Slide 14

CALIBRATION

TerraSAR-X calibration performance sets a solid basis

TDX-1 Calibration Goals

SAR Quality Parameter TDX-1 Calibration Goals

Absolute radiometric accuracy < 0.7dB

Internal calibration accuracy ≤ 0.1dB / ≤ 1.0 degree

Pixel localization accuracy ≤ 0.5m (range/azimuth)

Pointing accuracy < 2 mdeg (azimuth)

< 10 mdeg (elevation)

Antenna model accuracy ≤ 0.2 dB (requirement)


Slide 15

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 cornersMore than 1000 datatakeswill be analyzed

TDX-1 Monostatic Calibration Strategy


Slide 16

CALIBRATION

D01

x

D02

x D03 xD04

xD05

x

D06x

D07x

D24-D30

x x

x

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


Slide 17

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 for bistatic operation

Similar spectrograms


Slide 18

CALIBRATION

First results TDX-1: TRM Characterization – PN Gating

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

Receive

Ph

ase

[deg

rees

]A

mp

litu

de

[dB

]

Transmit

Ph

ase

[deg

rees

]A

mp

litu

de

[dB

]

Warm instrument stability


Slide 19

CALIBRATION

First Results TDX-1: Antenna Pattern over Rainforest

Within requirements




Slide 20

CALIBRATION

First Results TDX-1: Antenna Pattern by Ground Receivers

Ground Receiver

PositionVector

Transmit pattern only

Relative accuracy< ± 0.1dB

Measurements confirmsimulated reference pattern

Within requirements


Slide 21

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


Slide 22

CALIBRATION

Questions?

THE END

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

th1.l10.3: monostatic calibration of both tandem-x satellites

Documents

db stripmap

db antenna model

db channel imbalance

db radiometric stability

radiometric calibration

geometric calibration

monostatic calibration

azimuth tsx