MyOcean CDOM443

Summary

Provider: MyOcean (ACRI)

Contact person: ???

Contact for production: MyOcean Service Desk Send mail

Algorithm development:

CDOM443 is the coloured dissolved and detrital organic materials absorption coefficient at 443nm . As CDOM absorbs light it can have a significant effect on biological activity in aquatic systems: reducing the amount of light available for photosynthesis which, in turn, restricts phytoplankton growth. The presence of CDOM makes the assessment of remotely sensed phytoplankton more difficult.

Units: m-1.

Data Portal: MyOcean 2

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Platform & processing

Products available through MyOcean have been initiated in the frame of the GlobColour project funded by the ESA Data User Element Programme to develop a satellite based ocean colour data service to support global carbon-cycle research. Processed by ACRI in association with MyOcean. (In theory, the software is available, see http://www.odesa-info.eu/distrib/). The merged CDOM443 coefficient is generated using the GSM model from the 1/24° binned MODIS/SeaWiFS/MERIS daily L3 radiance products. Since 12 December 2010 this product has been derived from only MERIS and MODIS data which results in a possible degradation of spatial coverage.

Algorithm

CDOM443 is a product of the GSM (Garver-Siegel-Maritorena) technique.

Inputs to the GSM minimisation process are the fully normalised water leaving radiances Lxxx individually computed for each band and instrument, along with their associated error. The outputs of the GSM model are: CHL1, CDOM and BBP and their associated error.

See Garver and Siegel, 1997, Gordon et al., 1988, Maritorena et al., 2002, Maritorena and Siegel, 2005 (http://www.icess.ucsb.edu/~stephane/Marito_Siegel_merging_RSE.pdf)

Product uncertainties

Case 1 products may not work in case 2 waters depending on the nature of the water. Temporally the water may change through phytoplankton growth/decay, changes in nutrient inputs etc. Cloud cover limits coverage of the sea-surface. The error of the merged product when compared with in situ values was estimated to be 0.05.

Product dissemination

These products are not distributed via GEONETCast, but MyOcean sourced data are distributed via the internet.

Typical delay of near-real-time product is a minimum of 24hrs from acquisition of data by ACRI, and the delayed time product is 31 days.

Product validation

The GlobColour products have undergone an extensive validation based on a validation protocol derived from the SIMBIOS protocol. The GlobColour products have been derived with the GSM model and algorithm, developed by ICESS (Maritorena S. and D.A. Siegel. 2005). The GlobColour project has largely benefited from NASA contributions, including the availability of the MODIS and SeaWiFS products; the in situ data base of radiometric and phytoplankton pigment data, and other oceanographic and atmospheric data: the SeaWiFS Bio-optical Archive and Storage System - SeaBASS (Werdell and Bailey, 2002). Error statistics from the initial sensor characterisation are used as an input to the merging methods and propagate through the merging process to provide error estimates on the output merged products.

The chlorophyll-a algorithm has been peer reviewed, see references and the Product validation section of the Chlorophyll-a page

The GSM algorithm was calibrated with in-situ data primarily to establish sensor uncertainties used in the GSM approach. (see http://www.globcolour.info/validation/report/GlobCOLOUR_FVR_v1.1.pdf). MyOcean also provide a quality information document for ACRI products

Data characteristics

Global Ocean

Resolution: 4km, 25km and 100km.

Map projection: All resolutions now use regular equirectangular.

European Seas / North Africa

Coverage: 20°N to 85°N ; 45°W to 68° E. Can also be subsetted to the Mediterranean area (30°N to 46°N ; 6°W to 36.5° E) for download

Resolution: 2km

Map projection: regular equirectangular

Availability

Depends on processing type:

near-real-time: daily product, 31 day archive;

delayed time: daily product, 31 day archive;

reanalysis: daily, 8day, monthly product,

Flags for land/cloud, flags for bad radiometric quality of spectral bands (i.e. saturated pixels, sun glint etc.) have already been applied to input data. A separate flags product is available for download and documented here

Notes

Information about processing version changes are not widely disseminated. If processing changes the archive should usually be reprocessed for consistency with current NRT data although whether this mechanism is in place is not known.

Useful references:

Garver, S. A., & Siegel, D. A. (1997). Inherent optical property inversion of ocean color spectra and its biogeochemical interpretation: I. Time series from the Sargasso Sea. Journal of Geophysical Research, 102, 18607 - 18625.

Gordon, H. R., Brown, O. B., Evans, R. H., Brown, J. W., Smith, R. C., Baker, K. S., et al. (1988). A semi-analytic radiance model of ocean color. Journal of Geophysical Research, 93, 10909 - 10924.

Maritorena, S., Siegel, D. A., & Peterson, A. (2002). Optimization of a semi-analytical ocean color model for global scale applications. Applied Optics, 41(15), 2705 - 2714.

Maritorena, S., Siegel, D. A. (2005). Consistent merging of satellite ocean color data sets using a bio-optical model. Remote Sensing of Environment 94:429-440. [pdf]

Siegel, D. A. S. Maritorena, N. B. Nelson, M. J. Behrenfeld, and C. R. McClain. 2005. Colored dissolved organic matter and its influence on the satellite-based characterization of the ocean biosphere. Geophys. Res. Letters, 32, L20605, doi:10.1029/2005GL024310.