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
OCEAN COLOR DATA MERGING AT UCSB A BRIEF HISTORY : NASA SIMBIOS Program Develop merging procedures Test them with SeaWiFS and MODIS : 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 : ESA GlobCOLOUR Project GSM merging procedure is one of the methods tested.
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,…
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
RESULTS WITH THE NOMAD DATA SET
Merging technique = GSM model (Maritorena & Siegel, 2005) 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
SeaWiFS Aqua Merged Daily 9 km data - March 21, 2003 Meris
GSM - Merged SeaWiFS/Aqua/Meris - Daily (3/21/2003) Chl a cdm (443) GSM Chl [mg m -3 ] GSM a cdm (443) [m -1 ]
GSM - Merged SeaWiFS/Aqua/Meris 8-Day (May 24-31, 2003) Chl a cdm (443) GSM Chl [mg m -3 ] GSM a cdm (443) [m -1 ]
GSM - Merged SeaWiFS/Aqua/Meris Monthly Chl (July, 2002)
SeaWiFS vs. Aqua SeaWiFS vs. Meris Aqua vs. Meris 412 nm 443 nm 490 nm 555 nm L wN ( ) comparisons (Jan. 1, 2003)
GSM Merging Model Coverage map Chl product
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.
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
Daily coverage using SeaWiFS/Aqua and Meris (2003 data)
Sensor(s)Coverage (%)Std. Dev. (%) SeaWiFS Aqua Meris SeaWiFS/Aqua SeaWiFS/Meris Aqua/ Meris SeaWiFS/Aqua/Meris Ocean color sensors average daily coverage (2003 data)
coverage with composite images
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) data: R rs, Chl: 884 a cdm (443): 370 b bp (443): 178
Chl - latitudinal comparison SeaWiFSAquaMerisMergedSeaWiFS OBPG
Comparison of GSM and Meris products - Daily January 15, 2003 April 15, 2003
Validation and analyses of the model and products
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
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: 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: dods/data/oceancolor/ SeaWiFS Aqua Merged SeaWiFS Aqua
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
Thank you for your attention
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 )