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1 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 )santer@mren2.univ-littoral.fr Frascati, September2005
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2 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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3 Cirrus clouds
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4 Cirrus clouds over land Classification MERIS level 2: yellow (standard) and black ( using pressure product)
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5 CIRRUS MERIS 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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6 Sunglint
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7 GLITTER MERIS image of the ratio between the TOA radiance at 761 nm and 753 nm Lampedusa on the 16/07/2003
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8 Dust over England
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9 the Montserrat Volcano eruption
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10 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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11 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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12 Modelise the TOA signal over ocean in the O2 band 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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13 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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14 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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15 L toa = ( L atm + T * L g + t * (L w + L wc ) )T g Formulation of the signal
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16 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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17 Atmospheric transmittance
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18 Validity of the transmittance computation Rayleigh transmittances following Gordon and 6S
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19 Objective 3 Evaluate bias on the level 2 product due to inaccurate formulation of the signal Remediate
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20 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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21 AOT over water and over land Constance lake
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22 AOT over water and over land Balaton lake
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23 AOT over water and over land Constance lake Balaton lake
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24 IST-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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25 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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26 Objective 4 Aerosol remote sense over land can be alternatively used for AC over inland water Implement Validate
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27 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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28 MERIS, North of Germany, August, 13, 2003
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29 AOT_865
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30 Objective 5 quantify the adjacency effects –BRADEX
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31 Bradex
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