1. Toward a wider use of the Moon for In-flight Characterization
GSICS Annual Meeting
29th Feb.- 4th March 2016, Tsukuba, Japan
Toward a wider use of the Moon
for In-flight Characterization
An Overview
Bertrand Fougnie1, Sophie Lachérade1
Jack Xiong2
Pepe Phillips3, Thierry Marbach3
Marc Bouvet4
Stefan Adriaensen5
1 CNES 2 NASA-GSFC 3 EUMETSAT
4 ESA-ESTEC 5 VITO

2. Summary Current Calibration over the Moon
Used as a PICS for Monitoring (ROLO)
Radiometric properties of the Moon
Current (past) use of the Moon
Feedback from MODIS/VIIRS
Feedback from PARASOL
Feedback from Pleiades
Feedback from Proba-V
Expected/Future use of the Moon – under investigation
Post-EPS : 3MI and Metimage
Sentinel Missions : Sentinel-3 and Sentinel-2

3. Introduction The main current use of the Moon Moon for monitoring
Used by many (if not all) sensors through specific or opportunist acquisitions
But regular acquisitions
Monthly for fixed phase angle
Need model to consider libation or phase dependency
Definitively a powerful use
Many other characterization have been tested
 MODIS, VIIRS, Pleiades, Proba-V, PARASOL… among many others
Radiometric : cross-calibration, interband, MTF, straylight, response versus scan
Geometrical : registration
Highlight benefits for future uses which are under investigation
3MI, Metimage
Sentinel-3, Sentinel-2

4. Moon for monitoring
By “construction”, the Moon is a perfectly stable target (inherent property)
The integrated irradiance from lunar disk (apparent property) varies with
the geometry of the scene : respective positions between sensor/moon/sun
the considered spectral band
 Use of ROLO model to normalize results to a reference
Approach used by many sensors to monitor the degradation or evolution
Lachérade et al., SPIE, 2014
Xiong et al., SPIE, 2013
PHR-1A

5. Some of the properties of the moon…
Stability, but also other properties
 Out-of-Atmosphere Reference spectrum
convenient for interband calibration
convenient for calibration of absorption bands
(harder through vicarious tech.)
 Bright target over perfectly dark background
ideal dark for in-flight checking of the background level
offset, artifact, cross-talk…
perfect bright/dark transition for in-flight checking of the artifacts
PSF, MTF, straylight, ghosts, optical leak…
optimized contrast line for in-flight checking of geometry
band-to-band registration
 Stable target during large portion of the sensor orbit
ability to view several times the “same” moon
checking response versus scan or within field-of-view, multi-gain
sensitivity study

6. Current Use for MODIS/VIIRS
MODIS and VIIRS
Radiometric Calibration Stability
RSB (MODIS and VIIRS)
TEB (MODIS and VIIRS)
DNB (VIIRS)
Spatial Characterization
Along-scan and along-track BBR (MODIS and VIIRS)
Along-track MTF (MODIS and VIIRS)
Calibration Inter-comparison (MODIS and VIIRS)
Interband Characterization (MODIS and VIIRS)
Others
Optical Leak Characterization (MODIS)
Electronic Crosstalk Assessment (MODIS)
MODIS
VIIRS

7. Current Use for MODIS/VIIRS
Interband checking

8. Current Use for MODIS/VIIRS
MTF estimation
Spatial characterization (Band-to-band Registration)
Edge response function
Xiong et al., SPIE, 2013
Wang et al., CALCON, 2015

9. Current Use for MODIS/VIIRS
Before correction
Optical leak
Electronic crosstalk
Terra B35
From B31
to B32-36
Xiong et al., SPIE, 2013
Band 27
Jan 2002

10. Past Use for PARASOL PARASOL Interband normalization Full image
: opportunity for 1 moon acquisition during decommissioning
Small target, only 8 images
Sufficient to detect anomaly (offset)
Interband checking for absorption bands (763-O2, 9-H2O)
Tentative to check response within field-of-view
More acquisitions were needed…
Interband normalization
Full image
Region of
interest
Fougnie,
Pers. Comm., 2014

11. Current Use for Pleiades
Monitoring
Check consistency with acquisition geometry
Moonflower experiment
Cross-calibration with ODIS/VIIS :
Simultaneous Lunar Acquisition (LSO)
Phase angle matching
Xiong et al., SPIE, 2015
Lachérade et al., SPIE, 2014
PHR-1B vs VIIRS
PHR-1B vs MODIS

12. Current Use for Proba-V
Follow-on Végétation 1 & 2, developed by ESA
Proba : Launched in May 2013
Land surface
VEGETATION instrument = 4 bands from blue to SWIR , 300m, 2000km
No on-board device – Only vicarious calibration methods
Lunar acquisitions for monitoring
Assessment of straylight : checking consistency with the expected level
Dark current validation
MTF estimation
Sterck et al., 2014
Proba-V

13. Expected Future Use for Sentinel
ESA mission – operational service for the European Copernicus Program
S2A : Launched in June 2015
Land surface
MSI imager
MSI = 13 bands from 440 to 2200nm, 10/20/60m, 290km
On-board diffuser (nominal) + Vicarious calibration methods
MSI
Sentinel-2

14. Expected Future Use for Sentinel
ESA mission – operational service for the European Copernicus Program
S3A : launched in February 2016
Oceanography and land monitoring
Altimetry + 2 optical sensors OLCI and SLST (follow-on MERIS and AATSR)
OLCI = 21 bands from 410 to 1020nm, 300m, 1270km
SLSTR = 11 bands from 550 to nm, 500m/1km, 1400km
On-board diffusers + Black body (nominal) + Vicarious calibration methods
Sentinel-3A
OLCI
SLSTR

15. Expected Future Use for Sentinel
Sentinel expected characterization
Too late for S2a and S2B -> to be considered for 2C
Too late for S3a and S3B -> to be considered for 3C
Commissioning (possibly regular acquisitions)
 motivated, not decided, still under investigation
Configuration
Need for a manoeuver
A few acquisitions for commissioning
Which optimal phase angle for each goal ?
Characterization
Radiometric stability (1% over the lifetime) – only possible if regular acquisition
Absolute calibration (better than 2%) – will be possible in a couple of years
Interband calibration (better than 1%)
Straylight (1-2% at 50SSD from transition)
MTF
Flat field equalization

16. Future Use for Post-EPS / Metop-SG
Program EPS-SG (EUMETSAT polar system) launch 2021
3 satellites METOP-SG A : optical and sounder imagers
IASI-NG, Metimage, RO, MWS, Sentinel-5, 3MI
3 satellites METOP-SG B : microwave imager
Metimage
VII Visible Infrared Imager
Meteorology, Hi-res cloud products, aerosols, surface temperature
On-board diffuser + space view
EPS-SG
Metimage

17. Future Use for Post-EPS / Metop-SG
Metimage
On-board device to support in-flight calibration (including monitoring)
Moon intrusion occasionally captured in the cold space port during lifetime
Characterization
Currently documented for Commissioning (possibly regular)
Need at Beginning Of Life (BOL) more favorable phase angle than moon intrusion
Remove scan angle dependent artefacts from the space port view
Possible simultaneous lunar observation (SLO) with 3MI
Configuration
Need for a manoeuver
A few acquisitions for commissioning
Which optimal phase angle for each goal ?

18. 3MI: Multi-Viewing, -Channel, -Polarisation Imager
Dedicated to aerosol characterisation for: - Climate monitoring - Air quality monitoring and forecasting - Numerical Weather Prediction
2D Push-broom radiometer
(2200 km swath, 4 km pixel at nadir)
Provides images of the Earth TOA outgoing radiance using: - Multi-view (10 to 14 views; angular sampling in the order of 10°) - Multi-channel (12 channels from 410 to 2130 nm) - Multi-polarisation (9 channels with -60°, 0°, +60° polarisers)
POLDER heritage (PARASOL follow-on)
3MI

19. 3MI Acquisition Detectors Wheel Filters Optical heads 3MI image
2000 km
cross-track
along-track
3MI image
1 view: all spectral channels
(about 22 seconds)
up to 14 views: N = 7
(about 5 minutes) c
View 1 c
View N c
View 2N
Detectors
Wheel
Optical heads
Filters
Vsat
Target

20. Moon View Benefit for 3MI
3MI has no onboard calibration facility – Vicarious Methods
monitoring and calibration (including during commissioning time) will use the so-called vicarious calibration methods i.e. based on statistical use of reference scenes
final accuracy depends on various parameters
a significantly large number of acquisitions are required to reduce the uncertainty of each method
many radiometric aspects may limit the accuracy : the spectral knowledge, the straylight contamination, the polarization sensitivity, the linearity, etc…
absorption bands (763 nm, 910 nm, or SWIR-1370 nm) may have less accurate performances because of the difficulty to predict the observed signal
The benefit for a moon view would be multiple :
No atmospheric absorption allowing an immediate accurate inter-channel calibration (crucial for absorption bands)
Estimation of the system MTF (bright target over a perfectly dark background)
Diagnosis/validation of the stray-light correction performance (small target)
Cross-calibration with many sensors : METimage but also VIIRS, MODIS, Sentinel-3...
In general much effort will be saved for vicarious calibration on spectral assessment, absolute calibration, variation within the field-of-view, and cross-calibration
could be used to check the registration performances for polarized triplets and spectral bands or optical heads

21. Conclusion The moon is extensively used for monitoring
This requires regular acquisitions (scheduled or occasional)
Many other characterizations can be used for radiometric and geometrical purposes
Cross-calibration, Interband checking (absorption bands), absolute (coming), MTF estimation, straylight level checking or estimation, registration, response versus scan…
Moon is definitively a target that can be considered as an on-board device
Moon acquisition has to be considered as much as possible in the design of future system
Systematic acquisition is not the only approach : occasional viewing during (de)commissioning are also very precious
We (will) always learn something when viewing the moon
Thanks to all the contributors and co-authors…