Atmospheric correction over coastal and in land waters: Doing better with MERIS?
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Atmospheric correction over coastal and in land waters:
Doing better with MERIS?
Richard Santer
Université du Littoral Côte d’Opale
– 32, avenue Foch – 62930 Wimereux – FRANCE ( [email protected] )
Frascati, September2005
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Outlines• Improving flags using the oxygen band:
– Cirrus clouds– Sunglint– Stratospheric aerosols
• Improving analysis when flagged• Improving formulation of the signal for coastal
and inland waters– Adjacency effects– Alternative AC
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Cirrus clouds
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Cirrus clouds over land
Classification MERIS level 2: yellow (standard) and black ( using pressure product)
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CIRRUSMERIS image of the ratio between the TOA radiance at 761 nm and 753 nm
North Sea on the 31/03/2004
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Sunglint
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GLITTERMERIS image of the ratio between the TOA radiance at 761 nm and 753 nm
Lampedusa on the 16/07/2003
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Dust over England
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Birmingham East Harwell Plymouth Centre Rochester
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the Montserrat Volcano eruption
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Objective 1
• Use 761/765 for identification of specific events
• Illustrate the influence on products
• Correlate discrepancies on 761/765 and bias on products
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Outlines• Improving flags using the oxygen band:
– Cirrus clouds– Sunglint– Stratospheric aerosols
• Improving analysis when flagged• Improving formulation of the signal for coastal
and inland waters– Adjacency effects– Alternative AC
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Modelise the TOA signal over ocean in the O2 band
zTOA
zs
dz
sv
0
Ps
dP
smaOno T *
2
ss
Omm
Oaa
OO TTTT 2222
*
dPPmTP
TsP
Os
mO ).(
1 2
022
dzePmTH
T aHszz
zO
a
aO
s
/)(2 ).(
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5S formulation in the reference band at 753 nm
Introduction of specific O2 transmittances in the O2 band
Modelisation of these terms in the primary scattering approximation
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Outlines• Improving flags using the oxygen band:
– Cirrus clouds– Sunglint– Stratospheric aerosols
• Improving analysis when flagged• Improving formulation of the signal for coastal
and inland waters– Adjacency effects– Alternative AC
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Objective 2
• Use 761/765 product
• Illustrate the influence on level 2 products
• Correlate discrepancies on 761/765 product and bias on level 2 products
• Correct level 2 product
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L toa = ( L atm + T * Lg + t * (Lw + Lwc ) )Tg
Formulation of the signal
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The atmospheric path radiance
(a +ar) versus as at 865 nm (full line) and 443 nm (dashed lines) for 3 albedos : 0.6, 0.8 et 1.0
left: continental, right:maritime. o=60°, =0°, =90 (Gordon, 1997).
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Atmospheric transmittance
),(.1)(2
)(exp),( 3 ao
r tt
)(.),()(1exp),(
aaaa
Ft
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Validity of the transmittance computation
o = 30° o = 60°
tr (443) (Gordon) 0.87128 0.78768
tr (443) (6S) 0.87073 0.79777
Rayleigh transmittances following Gordon and 6S
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Objective 3
• Evaluate bias on the level 2 product due to inaccurate formulation of the signal
• Remediate
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IST-2000-28187 Satellite-based Information System on Coastal Areas and Lakes
AC over inland water
How are the ocean AC for inland water?
What alternative do we have?
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AOT over water and over land
Constance lake
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AOT over water and over land
Balaton lake
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AOT over water and over land
Constance lake Balaton lake
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24IST-2000-28187 Satellite-based Information
System on Coastal Areas and Lakes
How compare the GW and ML for the water products
Balaton Constance
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IST-2000-28187 Satellite-based Information System on Coastal Areas and Lakes
Paris, 13 December 2004
Water or land?
Good spatial homogeneity over land.
Over water, higher values correspond to a non null reflectance in the NIR.
Higher dispersion over water reflects the adjacency effect.
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Objective 4
• Aerosol remote sense over land can be alternatively used for AC over inland water
• Implement
• Validate
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IST-2000-28187 Satellite-based Information System on Coastal Areas and Lakes
Adjacency effect
• Light reflected by neighbourg pixels and scattered by the atmosphere towards the sensor– increases with contrast– increases with scattering
Land mask for the Fresnel reflection
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MERIS, North of Germany, August, 13, 2003
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AOT_865
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Pixel number
AO
T a
t 86
5 n
m
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Objective 5
• quantify the adjacency effects– BRADEX
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Bradex