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Error characterisation

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The user consultation carried out at the beginning of the Ocean Colour CCI project indicated an overwhelming preference for uncertainty characterisation based on comparison with in situ data. Each of the products, generated from a merged time series of ocean-colour data, has uncertainties (bias and Root Mean Square Difference) assigned to pixels based on the validation of each of the products against corresponding in situ observations. For further details please see the Uncertainty Characterisation Document (UCD) http://www.esa-oceancolour-cci.org/?q=webfm_send/321

In contrast, GlobColour products have pixel-by-pixel error bars based on a theoretical computation using a Look-Up-Table that uses the value of the variable and observation conditions or the output of the merging model. For further details consult the GlobColour Product User Guide at http://www.globcolour.info/CDR_Docs/GlobCOLOUR_PUG.pdf

Some OC_CCI observations don’t have a corresponding uncertainty.

This is because some pixels do not fit the currently pre-defined water classes, and thus OC-CCI-v1.0 and v2.0 don't currently have a computed uncertainty for them value; despite a product being produced. It’s expected this will be solved in the next data release.

What are the chlor_a_log10_rmsd and chlor_a_log10_bias values?

The Chlorophyll-a data were log transformed prior to the estimation of the uncertainty characteristics, using match-up in situ data, which means that the RMSD and bias are provided for log10(Chlorophyll).