CryoSat Interferometer Performance after 5 years in Orbit

1. CryoSat Interferometer
Performance after 5 years in Orbit
Michele Scagliola, Aresys
Marco Fornari, ESA
Jerome Bouffard, ESA

2. Outline
 Calibration of the CryoSat interferometer
 End-to-end performance and CryoSat requirement on across-track
accuracy/precision
 Improving the end-to-end performance of Cryosat Interferometer
by on-ground processing
 Conclusions

3. Calibration of
CryoSat Interferometer
End-to-end calibration of CryoSat interferometer:
 in orbit calibration campaigns rolling left and right the spacecraft of about ±0.4 deg
 the purpose is to deternine the across-track slope of the ocean surface
First arrival
Right
antennaLeft
antenna
q
χ
P
Satellite velocity
vector
Boresight direction
  
)/())0(( 0 BkArg 
Rh /1
the angle of the first
arrival from SARin L1b
roll mispointing angle
from Star Tracker
a geometric factor
Ocean surface
slope

4. Calibration of
CryoSat Interferometer
End-to-end calibration of CryoSat interferometer:
 in orbit calibration campaigns rolling left and right the spacecraft of about ±0.4 deg
 the purpose is to deternine the across-track slope of the ocean surface
 slope of ocean surface is known from geoid
The error between the measured angle of arrival (AoA) and
the expected AoA from geoid
First arrival
Right
antennaLeft
antenna
q
χ
P
Satellite velocity
vector
Boresight direction
 


 
geoid
m
error on the AoA coming from
the SIRAL and the IPF1
error on roll coming from star
tracker and on ground processing
Measured
error

5. Calibration of
CryoSat Interferometer
The end-to-end error on the AoA can be modeled as a linear function of the measured
AoA, so that the interferometer calibration function results in
-0.01 -0.005 0 0.005 0.01
-2.4
-2.3
-2.2
-2.1
-2
-1.9
-1.8
-1.7
-1.6
x 10
-3
Measured AoR [rad]
ErroronAoR[rad]
(q) = -0.025472q -0.0019043

m
(q)
0)(   a
phase departure [1] roll bias [1]
[1] Galin, N.; Wingham, D.J.; Cullen, R.; Fornari, M.; Smith, W.H.F.; Abdalla, S., "Calibration of the CryoSat-2
Interferometer and Measurement of Across-Track Ocean Slope," in Geoscience and Remote Sensing, IEEE
Transactions on , vol.51, no.1, pp.57-72, Jan. 2013
By analysis of the data acquired during the roll
calibration campaign, the interferometer calibration
parameters are computed
Interferometer
Calibration
function
ErroronAoA[rad]
Measured AoA [rad]
3996.1)588.9()(  ee 

6. End-to-end performance
and CryoSat requirements
The end-to-end performance of the CryoSat interferometer can be evaluated on the
residual error on the measured AoA after that the calibration function has been applied
   0  ammr
Residual
error
 r
 rSTD 
CryoSat System req.
on interferometer
Value E2E performance figure Symbol
Residual across-track
accuracy @2000km
141 μrad absolute average of the residual
error on AoA
Residual across-track
precision @1Hz
60 μrad standard deviation of the residual
error on AoA

7. Calibration campaigns:
BaselineC
Analysis of BaselineC CryoSat L1b SARin acquired during the roll campaigns
 below the requirements
 highly dependent on the Star Tracker that
provides the roll mispointing information
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
50
100
150
Time [mm-yyyy]
Abs.err.[10
-
6rad]
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
10
20
30
40
50
60
70
Time [mm-yyyy]
STD[10
-
6rad]
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 0
0
50
100
150
Time [mm-yyyy]
Abs.err.[10-
6rad]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement
Residual across-track accuracy Residual across-track precisions
 below the requirements
 independent of the Star Tracker that
provides the roll mispointing information
10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
Time [mm-yyyy]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement

8. Calibration campaigns:
BaselineC
Analysis of BaselineC CryoSat L1b SARin acquired during the roll campaigns
 below the requirements
 highly dependent on the Star Tracker that
provides the roll mispointing information
 below the requirements
 independent of the Star Tracker that
provides the roll mispointing information
 comparable to Instrument noise at L1B
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
50
100
150
Time [mm-yyyy]
Abs.err.[10
-
6rad]
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
10
20
30
40
50
60
70
Time [mm-yyyy]
STD[10
-
6rad]
10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
Time [mm-yyyy]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 0
0
50
100
150
Time [mm-yyyy]
Abs.err.[10-
6rad]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement
Residual across-track accuracy Residual across-track precisions
Instrument
noise at L1b

9. Improving the end-to-end
performance
An activity was started aiming at verifying if the end-to-end performance in
the sense of residual across-track accuracy can be still improved.
Following possible improvements have been identified
1. During on-ground processing of Star Tracker data, the aberration of the
light can be (properly) corrected: accuracy of the mispointing angle is
increased
2. A calibration function different for each Star Tracker can be computed
and then applied to SARin L1b data

10. Calibration campaigns:
aberration correction applied
Analysis of BaselineC CryoSat L1b SARin acquired during the roll campaigns
 much below the requirements
 independent on the Star Tracker that
provides the roll mispointing information
 No degradation applying aberration corr.
 independent of the Star Tracker that
provides the roll mispointing information
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
10
20
30
40
50
60
70
Time [mm-yyyy]
STD[10
-
6rad]
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
50
100
150
Time [mm-yyyy]
Abs.err.[10
-
6rad]
Residual across-track accuracy Residual across-track precisions
10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
Time [mm-yyyy]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014
0
50
100
150
Time [mm-yyyy]
Abs.err.[10-
6rad]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement

11. Calibration campaigns:
aberration correction applied
Analysis of BaselineC CryoSat L1b SARin acquired during the roll campaigns
 much below the requirements
 independent on the Star Tracker that
provides the roll mispointing information
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
50
100
150
Time [mm-yyyy]
Abs.err.[10
-
6rad]
Residual across-track accuracy
09-2010 04-2011 10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
0
50
100
150
Time [mm-yyyy]
Abs.err.[10
-
6rad]
Aberration correction not applied
10-2011 05-2012 11-2012 06-2013 01-2014 07-2014 02-2015
Time [mm-yyyy]
EECFI STR average
EECFI STR1
EECFI STR2
EECFI STR3
End-to-end requirement

12. End-to-end performance:
operational acquisitions
The end-to-end performance evaluated
on roll campaigns data
The end-to-end performance evaluated
on operational BacelineC SARin L1b
products
achievable end-to-end performance of
CryoSat Interferometer
Residual error minimized by
computation of the Calibration Function
operational end-to-end performance of
CryoSat Interferometer
The accuracy/precision of the SARin L1b
that are made available to science users

13. End-to-end performance:
operational acquisitions
End-to-end performance of CryoSat Interferometer from a dataset of more than 200
BaselineC SARin L1b products: all SARin L1b products acquired over a SARin patch in Indian
ocean, that has been active in operations from Nov. 2010 to May 2012 (about 17 months)
Definition E2E Accuracy on
AoA [rad]
E2E Precision on
AoA [rad]
Contribution to
height error [mm]
End-to-end requirement 141 60 14.6
BaselineC SARin L1B 105 32 6.8
Aberration correction applied
57 32 2.9
Aberration correction applied
Roll bias function of Star Tracker 21 32 1.0

14. End-to-end performance:
transponder acquisitions
The improvement in the sense of interferometer performance given by the
application of the aberration correction and by using a roll bias different for each
Star Tracker has been verified also by analysis of acquisitions over Transponder
Paper 303 - Session title: Cryosphere Posters
CRYO-6 - CryoSat-2, SIRAL Calibration with Transponder
Garcia-Mondejar, Albert (1); Fornari, Marco (2); Mertikas, Stelios (3); Bouffard,
Jerome (4); Roca, Mònica (1) 1: isardSAT Ltd.; 2: ESTEC, ESA; 3: Technical University of
Crete; 4: ESRIN, ESA

15. Conclusions
 The end-to-end performance of CryoSat interferometer have been within
system requirement from the beginning of the mission
 The residual across-track accuracy and precision for BaselineC SARin L1B
products has been assessed for science products
 Towards BaselineD, the residual across-track accuracy and precision for the
SARin L1B products can be still improved during on-ground processing
- More accurate mispointing angles can be obtained by applying the
aberration correction
- A proper roll bias for each Star Tracker can be compensated