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
RadiometricCalibration
Antenna Model
Cross Talk
RadiometricCalibration
Ant ModelVerification
GeoCal
TSX-1Re-Calibration
1 Month
AntPoint
Summer 2009
≈
Ope
ratio
nal P
hase
≈
TSX-1 / TDX-1 In-Orbit Calibration Plan
IGARSS 2010, Honolulu 29.07.2010Slide 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 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
IGARSS 2010, Honolulu 29.07.2010Slide 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
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]
IGARSS 2010, Honolulu 29.07.2010Slide 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 passAcross an areaof 750 x 750 km²
strip_003 strip_004 strip_005 strip_006
IGARSS 2010, Honolulu 29.07.2010Slide 7
CALIBRATION
Antenna Pattern Long Term Monitoring TSX-1
Shape deviationwithin
the main beamBeam-to-beamgain prediction
stable, no trendRequirement still fulfilled
Δ < ± 0.2dB
IGARSS 2010, Honolulu 29.07.2010Slide 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]
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.)
IGARSS 2010, Honolulu 29.07.2010Slide 9
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
IGARSS 2010, Honolulu 29.07.2010Slide 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
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)
IGARSS 2010, Honolulu 29.07.2010Slide 11
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
IGARSS 2010, Honolulu 29.07.2010Slide 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 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
IGARSS 2010, Honolulu 29.07.2010Slide 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 corners
More than 1000 datatakeswill be analyzed
TDX-1 Monostatic Calibration Strategy
IGARSS 2010, Honolulu 29.07.2010Slide 16
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
IGARSS 2010, Honolulu 29.07.2010Slide 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 forbistatic operationSimilar spectrograms
IGARSS 2010, Honolulu 29.07.2010Slide 18
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
IGARSS 2010, Honolulu 29.07.2010Slide 19
CALIBRATION
First Results TDX-1: Antenna Pattern over Rainforest
Within requirements
strip_003 strip_004 strip_005 strip_006
strip_003 strip_004 strip_005 strip_006
IGARSS 2010, Honolulu 29.07.2010Slide 20
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
IGARSS 2010, Honolulu 29.07.2010Slide 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