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 ( santer@mren2.univ-littoral.fr )

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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a va

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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 25 49 73 97 121 145 169 193 217 241 265 289 313 337 361 385

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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

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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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