Atmospheric correction over coastal and in land waters: Doing better with MERIS?

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 ) Frascati, September2005

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

3. Cirrus clouds

4. Cirrus clouds over land Classification MERIS level 2: yellow (standard) and black ( using pressure product)

5. CIRRUS MERIS image of the ratio between the TOA radiance at 761 nm and 753 nm North Sea on the 31/03/2004

6. Sunglint

7. GLITTER MERIS image of the ratio between the TOA radiance at 761 nm and 753 nm Lampedusa on the 16/07/2003

8. Dust over England

9. the Montserrat Volcano eruption

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

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

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

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

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

15. Formulation of the signal L toa = ( L atm + T * Lg + t * (Lw + Lwc ) )Tg

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).

17. Atmospheric transmittance

18. Validity of the transmittance computation Rayleigh transmittances following Gordon and 6S

19. Objective 3 • Evaluate bias on the level 2 product due to inaccurate formulation of the signal • Remediate

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?

21. AOT over water and over land Constance lake

22. AOT over water and over land Balaton lake

23. AOT over water and over land Balaton lake Constance lake

24. How compare the GW and ML for the water products IST-2000-28187 Satellite-based Information System on Coastal Areas and Lakes Balaton Constance

25. Water or land? IST-2000-28187 Satellite-based Information System on Coastal Areas and Lakes 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. Paris, 13 December 2004

26. Objective 4 • Aerosol remote sense over land can be alternatively used for AC over inland water • Implement • Validate

27. Adjacency effect IST-2000-28187 Satellite-based Information System on Coastal Areas and Lakes • 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

28. MERIS, North of Germany, August, 13, 2003

29. AOT_865

30. Objective 5 • quantify the adjacency effects • BRADEX

31. Bradex