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CNES Activities in the Framework of GSICS. Patrice Henry, Denis Blumstein, Denis Jouglet - CNES Thomas Colin - CS. Intercalibration AIRS/IASI SNO events (high latitude only) operational in the IASI TEC activated on a regular basis 3 months - PowerPoint PPT Presentation
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GSICS Executive Committee – WMO Geneva – June 06-08 2011
CNES Activitiesin the Framework of GSICS
Patrice Henry, Denis Blumstein, Denis Jouglet - CNES
Thomas Colin - CS
2GSICS Executive Committee – WMO Geneva – June 06-08 2011
AIRS/IASI Intercalibration — sample of results
■ Intercalibration AIRS/IASISNO events (high latitude only)operational in the IASI TECactivated on a regular basis
3 months
■ Updated to handle IASI L1C Day-2 products (from May 2010)
3GSICS Executive Committee – WMO Geneva – June 06-08 2011
MetopA/IASI-A MetopB/IASI-B
~39°
common zone
16km
10km
IASI-A / IASI-B Intercalibration — Cal/Val preparation
■ Metop-A / B are on the same trajectory (180 deg apart) Overlap between the swath of the 2 IASI instruments
■ Observation by 2 IASI of a same region on ground possible 50 min between overflight of a same point At all latitudes
■ Use of common zone where Sat Viewing Angle are “equal” We limit ourself to 4 IASI pixels width Satellite Viewing Angle between 0 deg (high latitude) and 39 deg
(equator)
■ Limitation to uniform and stable (in time) geophysical situation
IASI-A IASI-B
common view by
IASI-A / IASI-B
4GSICS Executive Committee – WMO Geneva – June 06-08 2011
Study of Asian and Australian Desert Sites forSensor cross-Calibration in the VPIR Range
■ Sites selected in 2009 by B.J. Sohn using MODIS data Simpson desert (Australia) – 50x50 km2, centered at 26.075S, 137.175E Tengger desert (China) – 17x17 km2, centered at 38.125N, 103.0E
■ CNES studies Extraction of POLDER/PARASOL and SPOT5/VGT2 images over a 2 year period (2007-08) Data processing (cloud screening…) and insertion in the SADE data base Sites analysis using ‘standard’ CNES tools
Spatial, spectral, temporal and directional behaviour PARASOL and VGT2 cross calibration
Results comparison with 3 African desert sites : Algeria 3, Libya 1 and Libya 3
■ For the 2 sites : less suitable characteristics for calibration than African sites Tengger
Very small site and not so homogeneous Calibration standard deviation much higher than for other sites No winter calibration opportunity (potential snow coverage) and poor results for sensors cross calibration
Simpson Lightly less homogeneous than African sites Poor temporal stability : bad results for multidate calibration
■ No SADE extension with other PARASOL and VGT2 data but MERIS data will be added
5GSICS Executive Committee – WMO Geneva – June 06-08 2011
Simpson Tengger
Algeria 3
Libya 1
Libya 3
General view of the 5 sites
6GSICS Executive Committee – WMO Geneva – June 06-08 2011
Sites temporal behaviour
Spectral dependance of seasonal effect on spectral range for Tengger
(vegetation ?)
Simpson Tengger
Algeria 3 Libya 1 Libya 3
PARASOL TOA reflectance normalized by the red reflectance
7GSICS Executive Committee – WMO Geneva – June 06-08 2011
VGT2 calibration versus Parasol
Mean VGT2/PARASOL calibration results
• Good consistency for the red range
• Simpson : 3% higher in the blue, 3% lower in the NIR
•Tengger : 6% higher in the blue (very high …)
Standard deviation of VGT2/PARASOL calibration results
8GSICS Executive Committee – WMO Geneva – June 06-08 2011
Multitemporal calibration
PARASOL 2008 calibration versus PARASOL 2007
• Good for Tengger (except blue)
• A few percent discrepancy for Simpson (temporal stability ?)
VGT-2 2008 calibration versus VGT-2 2007
9GSICS Executive Committee – WMO Geneva – June 06-08 2011
■ Study performed to provide inputs for deserts calibration error budget
■ TOA reflectance of different sensors (MODIS, MERIS, PARASOL, VGT, ETM+) simulated using Hyperion hyperspectral TOA data
Aqua/MODIS vs MERIS
MERIS vs Aqua/MODIS
ETM+ vs Terra/MODIS
VGT2 vs Parasol/POLDER
Parasol/POLDER vs Aqua/MODIS
Parasol/POLDER vs MERIS
■ Different cross calibration method tested :
Same geometry (data pairs simulated with the same Hyperion data)
Close geometry (data pairs from close geometry Hyperion pairs)
Closest spectral band (direct band to band comparison to spline interpolation)
Omitted spectral bands to assess interpolation and extrapolation effect
Deserts cross Calibration Method Assessment
10GSICS Executive Committee – WMO Geneva – June 06-08 2011
■ Comparison of same geometry and close geometry calibration
Example of Aqua/MODIS vs MERIS
Acquisition geometry error
Same geometry Close geometry
■Very important increase of standard deviation (x2 to x10) but small effect on the mean value (0.5% max.)
But viewing geometry is always the same (Hyperion geometry). Discrepancies are only due to : sun angles, atmospheric correction, annual variation of the site
11GSICS Executive Committee – WMO Geneva – June 06-08 2011
■ Comparison of spline interpolation and band to band calibration
Example of Landsat/ETM+ vs Terra/MODIS
Reflectance interpolation error
Spline interpolation Band to band
■ Increase of cross calibration unaccuracy
■ Increase of site to site discrepancy
Band to band calibration shall be limited to very similar bands (VGT2/VGT1, Aqua/MODIS vs Terra/MODIS…)
12GSICS Executive Committee – WMO Geneva – June 06-08 2011
■ Comparison of cross calibration with different set of reference band
Example of Aqua/MODIS vs MERIS
Without 412 nm as reference band
■Very important error due to extrapolation (> 20%)
Site reflectance profiles do not allow any extrapolation neither in the blue or in the SWIR…
Reflectance extrapolation error
With 412 nm as reference band
13GSICS Executive Committee – WMO Geneva – June 06-08 2011
■ Interpolation (extrapolation !) error : main contributor of the error budget
Adequate choice for the reference sensor
Good knowledge of the site reflectance
Good knowledge of the directional effects over the sites
■ Statistics can take afford for atmospheric correction errors
Necessity for a great amount of data
Risk a small bias due to uncertainty on aerosol content
■ Good accuracy for multitemporal calibration
■ Sensors cross calibration only possible for ‘close’ spectral bands
a more complete error budget has been undertaken
Main Conclusions of the Study
14GSICS Executive Committee – WMO Geneva – June 06-08 2011
■ Few feedbacks from beta-users : only one (very positive…)
■ SADE access through CNES scientific mission website
http://smsc.cnes.fr/CALIBRATION/
Password mandatory
■ No procedure yet available for password delivery (contact Denis Blumstein or Patrice Henry)
■ A complete reprocessing of SADE exported files is foreseen for Nov. 2011
Data extension up to mid 2011
New sensors :
Terra/Modis
Landsat 7
Theos
New MERIS reprocessing
VGT1 updated calibration
SADE opening to GSICS and CEOS