The Image Quality Center for PROBA-V

08/07/2013
The Image Quality Center for PROBA-V: How to
maintain the image performance after launch?
Sindy Sterckx
IQC
Image Quality
center
IQC-RC
IQC-GC
Stefan Adriaensen
Wouter Dierckx
Stefan Livens
Sindy Sterckx
Iskander Benhadj
Geert Duhoux
Supported by ACS
08/07/2013
© 2013, VITO NV
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IQC –Radiometric Calibration
» Reliable, accurate and consistent measurements
» Variations in the characteristics of the instrument are likely to occur in orbit
due to
» outgassing phenomena during launch
» aging of the optical parts,…
» In-flight calibration
» with on-board calibration devices such as lamps, solar diffuser panels,
LEDs,..
» Vicarious calibration techniques :
Calibration against a non-standard reference by (source) making use
of natural (or artifical sites)
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© 2013, VITO NV
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Radiometric Performance Requirements
» 5 % absolute accuracy
» 3 % relative accuracy
»inter-band
»multi-temporal
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© 2013, VITO NV
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RC – IQC: Vicarious Calibration Concept
Absolute
OSCAR* (Optical Sensor Calibration
with simulated Radiances)
» Relies on combination of various
vicarious calibration methods to
reduce uncertainty in the calibration
results and to verify the different
requirements
Antarctica/
Greenland
Temporal
Oceans
Sun
Deserts
DC Clouds
Multi Angular
08/07/2013
© 2013, VITO NV
Glint
Interband
*Sterckx et al. IJRS, in5 Press
Desert calibration
Target: stable, homogenous desert sites
Method: compare TOA radiances to simulated values
Usage : Operational absolute calibration for all bands , cross mission calibration,
multi-temporal
PROBA-V image 26/06
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© 2013, VITO NV
Adriaensen et al., 2012 (CEOS report); Govaerts et
al., RSL 2013
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Rayleigh calibration
Target: stable, homogenous oceans
Method: compare TOA radiances to simulated values,
using NIR band to retrieve aerosol optical depth
Usage : Operational absolute calibration, for RED and BLUE
combine with inter-band to transfer results to NIR, SWIR
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© 2013, VITO NV
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Sterckx et al. TGARS,
2013
Rayleigh calibration
Application to VGT
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Deep Convective Clouds calibration
Target: reflection of deep convective clouds over oceans
Method: Compare PROBA-V TOA data to simulated data using RED band as
reference band to retrieve cloud optical thickness”
Usage: inter-band (absolute if combined)
08/07/2013
© 2013, VITO NV
PROBA-V
image 24/06
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Sun Glint Calibration
» Target: white specular reflection of sun over oceans
» Method: compare PROBA-V TOA data to simulated data
» Usage : inter-band (absolute)
reference: RED band to retrieve wind speed.
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© 2013, VITO NV
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Lunar Calibration
Moon = stable over thousands of years
Usage : stability monitoring
Implementation :
• Compute integrated irradiance
• Convert integrated irradiance to full disc
reflectance and compare with a lunar
reflectance model
• Monthly acquisition at same phase
PROBA-V image 23/06
angle to reduce uncertainty
Other usage :
 MTF
 Dark current validation
 Straylight assessment
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© 2013, VITO NV
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Experimental calibrations : the linearity check
Integration time changes in steps over
homogenous areas
PROBA-V image 17/06
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© 2013, VITO NV
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Vicarious Calibration Concept
Statistically combine
results of different methods
to reduce uncertainty
reconcile methods
temporal: time series
averaging over sites
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© 2013, VITO NV
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RC- Image Quality Center: HMI
•
•
•
•
fully automated image workflows and statiscal processing
View at the database using Graphical User Interface
Full traceability new instrument calibration parameters updates
Automated distribution towards PF
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© 2013, VITO NV
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First results on Libya-4
desert site ……
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Instrument Programming Center (IPC)
• Communication with Mission Control Center (MCC) for acquisitions
• with specific instrument settings
• over non-nominal sites
• with maneuvers
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Instrument Programming Center (IPC)
• validate requests against resource constraints
• send request to the Mission Control Center (MCC)
• monitors their uploading and execution
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© 2013, VITO NV
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IPC – IQC HMI
Calibration request
status follow-up
IQC workflows
automatically started
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© 2013, VITO NV
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IQC
Image Quality
center
IQC-RC
IQC-GC
Stefan Adriaensen
Wouter Dierckx
Stefan Livens
Sindy Sterckx
Iskander Benhadj
Geert Duhoux
Supported by ACS
08/07/2013
© 2013, VITO NV
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Geometric calibration objectives
Main objective of the In-flight GC is :
To assure that the geolocation accuracy requirements
for the PROBA-V end products can be met
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© 2013, VITO NV
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In-flight geometric calibration
» major challenges :
»
»
»
»
»
3 camera’s
VNIR and SWIR detectors mounted on different locations
VNIR and SWIR with different Ground Sampling Distances (GSD)
SWIR detector composed of 3 overlapping detectors
No active onboard thermal control
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© 2013, VITO NV
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IQC – Geometric Calibration
» Estimate and monitor on a regular basis :
 The exterior orientation (boresight misalignement angles)
 The interior orientation deformations (CCD viewing direction
vectors)
» To account for
 distortions within one orbit (time since exit from eclipse)
 slow varying errors (seasonal effects) (sun beta angle)
» To update the ICP to guarantee the geometrical system accuracy of
the system corrected products.
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© 2013, VITO NV
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GC- Image Quality Center: HMI
08/07/2013
© 2013, VITO NV
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Geolocation error: preliminary results
Scatter plot of absolute
geolocation error (m) BLUE band
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© 2013, VITO NV
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Conclusions
» Pre-flight studies showed that the mission requirement specifications for
the radiometric calibration, i.e., 5% absolute and 3% relative should be
realistic achievable goals for the PROBA-V missions although no on-board
calibration devices are available
» The calibration concept of combining different vicarious calibration
methods which cover different parts of the dynamic range of the sensor
(dark oceans versus bright clouds), and which are using different
references minimizes biases or systematic errors which may occur if only
one method is used.
» Preliminary radiometric calibration results are very promising
» Preliminary geolocation assessment results :
» mandatory requirements already achieved
» realization of the goal requirements = a realistic goal, achievable by
the end of commissioning
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© 2013, VITO NV
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Thank you!
IQC-RC : Sindy Sterckx
Sindy.sterckx@vito.be
IQC-GC : Iskander Benhadj
Iskander.benhadj@vito.be
VITO – Flemish Institute for Technological Research
Boeretang 200, B-2400 Mol, Belgium
08/07/2013
© 2013, VITO NV
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