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. Outlines. - PowerPoint PPT PresentationTRANSCRIPT
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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
transect 1
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1 21 41 61 81 101 121 141 161 181 201 221points
da
ta v
alu
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L_778
L_865
L_761/L_753 (*100)
transect 2
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1 14 27 40 53 66 79 92 105 118 131 144 157 170 183
points
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L_865
L_761/L_753
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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
transect 1
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1015
2025
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1 29 57 85 113 141 169 197 225 253 281 309 337 365 393
points
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1 25 49 73 97 121 145 169 193 217 241 265 289 313 337 361 385
points
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Dust over England
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80
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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
12
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
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
Transect
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1 15 29 43 57 71 85 99 4 18 32 46 60 74 88 102
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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