1. The GSM merging model. Previous achievements and application to GlobCOLOUR Globcolour / Medspiration user consultation, Dec 4-6, 2006, Villefranche/mer Stéphane Maritorena, Dave Siegel ICESS University of California, Santa Barbara

2. OCEAN COLOR DATA MERGING AT UCSB A BRIEF HISTORY 1997 - 2003: NASA SIMBIOS Program Develop merging procedures Test them with SeaWiFS and MODIS 2004 - : NASA Research, Education, and Applications Solution Network (REASoN) Develop an Ocean Color Time-series Develop and distribute merged data sets from SeaWiFS and MODIS: Chl and other products 2005 - : ESA GlobCOLOUR Project GSM merging procedure is one of the methods tested.

3. Why do ocean color data merging ? Several simultaneous global ocean color missions Several versions of the same product Benefits: Development of unified, consistent ocean color time-series from multiple sensors (ESDRs, CDRs) Improved spatial and temporal coverage More diverse ocean color products with lower uncertainties Difficulties: Sensors are not created equal: different designs, calibrations, algorithms, accuracies,…. Large volumes of data to deal with Merging procedure should not create biases, discontinuities, artifacts,…

4. THE GSM01 MERGING MODEL (Garver & Siegel, 1997; Maritorena et al., 2002; Maritorena & Siegel, 2005). Non-water components of absorption and scattering are expressed as known shape functions with an unknown magnitudes: a ph ( ) = Chl a ph *( ) a cdm ( ) = a cdm (443) exp(-S( -443)) b bp ( ) = b bp (443) (  /443) -  Fixed parameters were optimized for global applications using a large in situ data set Non-linear least-square technique is used to solve for the unknowns (chl, a cdm (443) and b bp (443)) from L wN ( ) data at 4 or more wavelengths. Uncertainties of the input L wN ( ) can be taken into account. Confidence intervals of the retrievals are estimated GSM01 is a Case I non-polar water model

5. RESULTS WITH THE NOMAD DATA SET

6. Merging technique = GSM model (Maritorena & Siegel, 2005) 412 443 490 510 555 412 443 488 531 551 412 443 490 510 560 412 443 490 510 531 551 555 560 SeaWiFS Aqua Meris Merged 9 km grid (REASoN) 4.6 km grid (GlobCOLOUR) GSM main features: Exploits band differences to extend spectral information Utilizes band redundancies Uncertainties of the input L wN ( ) can be taken into account. Can provide uncertainty estimates for the output products GSM01 forward L wN ( ) QC

7. SeaWiFS Aqua Merged Daily 9 km data - March 21, 2003 Meris

8. GSM - Merged SeaWiFS/Aqua/Meris - Daily (3/21/2003) Chl a cdm (443) 1.00 0.1 0.01 GSM Chl [mg m -3 ] GSM a cdm (443) [m -1 ] 1.00 0.01 0.001 0.1

9. GSM - Merged SeaWiFS/Aqua/Meris 8-Day (May 24-31, 2003) Chl a cdm (443) 1.00 0.1 0.01 GSM Chl [mg m -3 ] 1.00 0.1 0.001 0.01 GSM a cdm (443) [m -1 ]

10. GSM - Merged SeaWiFS/Aqua/Meris Monthly Chl (July, 2002)

11. SeaWiFS vs. Aqua SeaWiFS vs. Meris Aqua vs. Meris 412 nm 443 nm 490 nm 555 nm L wN ( ) comparisons (Jan. 1, 2003)

12. GSM Merging Model Coverage map Chl product

13. Issues with the particulate backscattering product Meris issue Mostly a SeaWiFS issue  Noise in the SeaWiFS and Meris Lwns around gaps caused by clouds. In these areas, the Lwn( ) are sometimes higher than in nearby gap-free areas and this results in enhanced b bp (443) values.  Problem seems much less important in Aqua data  This noise is not uniformly distributed but seems to mostly affect mid-latitudes in the southern hemisphere.  Meris shows some high b bp values on the western edge of some swaths.

14. SeaWiFS L wN (555) SeaWiFS b bp (443) Noise in the backscattering product with SeaWiFS “Ringing” issue High L wN ( ) values around cloud gaps Can be filtered but will result in loss of coverage Does not happen with Aqua data

15. Daily coverage using SeaWiFS/Aqua and Meris (2003 data)

16. Sensor(s)Coverage (%)Std. Dev. (%) SeaWiFS16.652.01 Aqua13.761.15 Meris8.51 1.48 SeaWiFS/Aqua24.221.94 SeaWiFS/Meris22.242.40 Aqua/ Meris19.921.74 SeaWiFS/Aqua/Meris28.852.241 Ocean color sensors average daily coverage (2003 data)

17. coverage with composite images

18. Matchups w/ NOMAD (97-03) + SeaBASS (04-06) data Nomad data: R rs, Chl: 2203 a cdm (443): 535 b bp (443): 181 Chl a cdm (443) b bp (443) 2004-2006 data: R rs, Chl: 884 a cdm (443): 370 b bp (443): 178

19. Chl - latitudinal comparison SeaWiFSAquaMerisMergedSeaWiFS OBPG

20. Comparison of GSM and Meris products - Daily January 15, 2003 April 15, 2003

21. Validation and analyses of the model and products

22. What to do with the merged data sets ? What we are currently doing at UCSB:  Eddies and open ocean biogeochemistry in the Sargasso Sea  Export particle source regions and the horizontal advection of sinking particles  Spring blooms  CDOM in the Southern Ocean  Spatial structure/decorrelation scales What we are currently doing at UCSB:  Eddies and open ocean biogeochemistry in the Sargasso Sea  Export particle source regions and the horizontal advection of sinking particles  Spring blooms  CDOM in the Southern Ocean  Spatial structure/decorrelation scales

23. NASA REASoN GSM Merged data sets global 9 km daily weekly (8D) monthly Chl(+ confidence intervals for dailies) a cdm (443)(+ confidence intervals for dailies) b bp (443) (+ confidence intervals for dailies) coverage map Product files in HDF format, compressed (4320 x 2160 arrays) Merged SeaWiFS-Aqua, SeaWiFS only, Aqua only. Available at: ftp:ftp.oceancolor.ucsb.edu/pub/org/oceancolor/REASoN OPeNDAP server: http://dap.oceancolor.ucsb.edu/cgi-bin/nph- dods/data/oceancolor/ NASA REASoN GSM Merged data sets global 9 km daily weekly (8D) monthly Chl(+ confidence intervals for dailies) a cdm (443)(+ confidence intervals for dailies) b bp (443) (+ confidence intervals for dailies) coverage map Product files in HDF format, compressed (4320 x 2160 arrays) Merged SeaWiFS-Aqua, SeaWiFS only, Aqua only. Available at: ftp:ftp.oceancolor.ucsb.edu/pub/org/oceancolor/REASoN OPeNDAP server: http://dap.oceancolor.ucsb.edu/cgi-bin/nph- dods/data/oceancolor/ SeaWiFS Aqua Merged SeaWiFS Aqua

24. NASA REASON future developments: 3- or 4-Day composites Merge Terra data if/when available More validation and analyses of the merged products More user-friendly interface sub-sampling, slicing Integration into NASA Giovanni system New products

25. Thank you for your attention

26. The GSM01 model Gordon et al., 1988 a ph ( ) = Chl a ph *( ) a cdm ( ) = a cdm ( 0 ) exp[-S( - 0 )] b bp ( ) = b bp ( / 0 ) 