6th Aquarius/SAC-D Science Meeting
MWR Calibration
pre-launch & post launch
Juan Cruz Gallo (CONAE)
Daniel Omar Rocca (IAR)
Linwood Jones (CFRSL)
Sakay Biswas (CFRSL)
19-21 July 2010
Seattle, Washington, USA
MWR Radiometric Calibration Plan
Pre-launch
 Receivers calibration using hot/cold
loads
• Calibration and Stability verification
@ laboratory
 End to end calibration on Thermo
Vacuum Chamber using absorbers
• feeds without reflectors
Post-launch
 Cold Sky
• Monthly satellite CSC maneuver
 Vicarious Calibration
 Inter-satellite Calibration
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
2 of 19
July 19-21, 2010
MWR Pre-launch calibration
Pre-launch calibration will be performed using two Independent
methods:
1) By CONAE-IAR
• Radiometer transfer function: uses empirical linear regression
equation (thermal vac data)
• Used for level-1 processing (counts to earth scene brightness
temp, Tap)
• Antenna: Antenna pattern correction
2) By CFRSL
• Theoretical radiometric transfer function (counts to Tap)
• Switch Matrix mathematical model
• Relates antenna brightness temp (Tant) @ receiver input to
earth scene brightness temp (Tap) collected by feeds
• Linear receiver transfer function
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
3 of 19
July 19-21, 2010
MWR Pre-launch calibration
Receivers calibration using hot/cold loads @ laboratory







Vv   Gvv
 
Vh   0

Vp   G pv
 
Vm   Gmv
0
Ghh
G ph
Gmh
0 

0 
G pU 

GmU 
 ov 

 Tv  

  oh 
 Th   

 T   op 
 U  o 
 m 
V : Voltage at detector output matrix
G : Gain matrix
T : Brightness temperatur e matrix
o : Offset matrix
Note: based on ”Calibration of Passive Microwave Polarimeters that Use Hybrid Coupler-Based Correlators”, J.
R. Piepmeier IEEE Trans. Geosci. Remote Sensing, Vol. 42, No. 2, February 2004).
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
Pre-launch calibration
Ta Receiver Calibration
Raw Data
Ca, Cn, Co
D
TA '  ηL TA  ( 1 - ηL ) TFA
C o  C a Vo  Va (TOR  TAR )


C n  C a Vn  Va TNR  TAR 
TFA: Physical Antenna (Horn) Temperature
L: Antenna Radiation Eficiency
The components temperature must be controlled 1 ºC and they temperature measured
with an accuracy of  0.1 C
Ta 

 (1   L )( FC  1) 


L 2 .L1 .FC 
(1  FC )
D
D
 TO  





TF

1



TF


T
A
N
 L .L .F

 L .L .F

ON 
 L (FC  1) 
L
.
L
.
F
L
.
L
.
F
2 1 C
2 1 C
2 a2 C 
2 a2 C




TA   0  1.T0   2 .TFA  3 .TF   4 .TF .D  5 .D.TN
Quadratic correction are been considered to improve the residual non linearity of the diode
detectors
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
Radiometer Calibration Plan
Determination of the i coeficients
TA   0  1.T0   2 .TFA  3 .TF   4 .TF .D  5 .D.TN
i are estimated by multi-linear regression of data taken when their
temperatures were varied in a linearly independent manner, this data is
taken during the thermal Vacuum Test. This procedure was used by
Topex calibration Team (IEEE:TOPEX Poseidon Microwave Radiometer
(TMR): I. Instrument Description and Antenna Temperature Calibration)


TCAL  . 
 TCAL 1  

 
 TCAL 2  
  

 
   
T

 CAL h  
1
T0 1
TFA 1
TF 1
D1.TF 1
1
T0
TFA
TF2
D2 .TF










1
T0
2
TFA
h
2
h
TFh
Dh .TF
2
h
D1.TN    0 
 
D2 .TN   1 
 .  
 
   
Dh .TN    5 

The vector of coefficients, , is estimated from the data by minimum
squared error inversion:
  T . .T .TCAL

6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
1

Where TT denotes the matrix
transpose operation.
6 of 19
July 19-21, 2010
Pre-launch calibration
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
7 of 19
July 19-21, 2010
Antenna pattern correction
Ulaby-Antenna Pattern Correction
1
1 - ηM
1 - ηL
TA ' TSL TFA
ηM ηL
ηM
ηM ηL
TML 
TA '  ηL TA  ( 1 - ηL ) TFA
TA: Antenna Apparent Temperature
TFA: Physical Antenna (Horn) Temperature
L: Antenna Radiation Efficiency
M: Antenna Main Lobe Efficiency
TSL: Side-Lobe Temperature contribution

TSL 
4π-

TAP ( θ ,  ) Fn ( θ ,  ) dΩ
Main
Lobe

4π-
Fn ( θ ,  ) dΩ
ηM 
Fn ( θ ,  ) dΩ
Main
Lobe
 F
n ( θ , )
dΩ
4π
Main
Lobe
ηL 
Go
4Go

Do  Fn ( θ ,  ) dΩ
Fn(,)= Normalized Radiation Pattern
Go=Maximum Power Gain
Do=Maximum Directivity
4π
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
Antenna pattern correction
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
CFRSL Pre-launch calibration
• Calculate individual feed-horn
path losses for both pols
• Model theoretical radiative
transfer based on dissipative
losses and leakage coupling
• Validate model using CONAE
thermal vacuum test data
•Receiver: Non-linearity analysis
using noise diode deflection test.
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
Cold-Space Radiometric Calibration
• During SAC-D pitch maneuver MWR
antenna beams will view cold-space
– Cosmic brightness temp Tb = 2.73 K
– Isotropic and homogeneous
• Allows radiometric inter-calib
between 24 MWR beams
– Validation of radiometric transfer function
• Does not assess antenna pattern
affects on calibration
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
Inter-Sat Radiometric Calibration
• Normalizes MWR’s Tb calibration to other conical
scanning radiometer systems
–
–
–
–
WindSat Polarimetric Radiometer
TRMM Microwave Imager
SSMI
AMSR
• Leverages off NASA’s microwave radiometer Intersat Calib Working Group (X-cal) activities
– Uses near-simultaneous and spatially collocated Tb observations
between a pair of sat radiometers
– Tb normalization to account for expected freq and geometry
differences
– homogeneous ocean and land scenes
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
12 of 19
July 19-21, 2010
Near-Simultaneous Match-up Data Sets
GDAS Env.
Parameters
MWR Tb Data
Match-up Data File
Collocated
Points
WindSat L1C
Tb Data
• Match-ups within ±45 minutes & spatial quantization of
one degree latitude & longitude
• Thousands of collocation files generated / day
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
13 of 19
July 19-21, 2010
MWR Swath Direction Ascending
AQ/SAC-D orbit is lower altitude, therefore AQ travels
faster and laps WindSat every ~ 2 days
Flight Direction
Swath
Direction
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Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010
MWR Swath
• MWR swath to the right of sat
sub-track for ascending track
652 km
272 km 380 km
• WindSat & Aquarius orbits drift
into and out of phase
– Orbit Phasing period
• ~ 30 days to repeat ground track
• Collocation efficiency > 60%
– Worst case temporal collocation
• ± 45 min (half-orbit period)
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
Swath
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July 19-21, 2010
AQ/WindSat Collocations for 45 hrs
• Approx 19,000 collocations in 45 hrs (± 50o Lat)
• (0.5o x 0.5o) & ± 45 min window
• Approx 1 Million ocean collocations in 5 months
6th Aquarius/SAC-D Science Meeting
Seattle. MWR Calibratio – Jones-Gallo
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July 19-21,162010
Warm Bias (Land) Calibration Targets
Example of TMI/WindSat 1°x1° blackbody calibration sites ± 1hr
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July 19-21, 2010
•Conclusions
• Pre-launch Calibration will be checked using two methods:
• CONAE-IAR based on empirical data
• CFRSL based on radiometer physical model
• Intercomparison of two independent methods
• Post-launch calibration
• Inter-satellite calibration using WindSat
• CSC
• Other possibility will be studied
• e.g. Vicarius calibration
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Seattle. MWR Calibratio – Jones-Gallo
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July 19-21, 2010