OCEANcode: the complete set of algorithms and models for the level_2 processing of European CZCS historical data

A complete set of algorithms and models for the level_2 processing of the E uropean CZCS historical data was integrated in the OCEANcode software packa ge. The OCEANcode allows the calibration of the sensor-recorded signal taki ng into account the instrument sensitivity loss; the correction of the cali brated signal for atmospheric contamination and derive sub-surface reflecta nces; and then the estimation of the concentration of water constituents. T he atmospheric correction is performed on the basis of a reflectance-model- based algorithm. The Rayleigh correction is applied consistently for all wa ter pixels, using a multiple scattering approach, and introducing atmospher ic pressure and Ozone concentration data in the computation. The marine aer osol correction uses a pixel-by-pixel iterative procedure, allowing success ive estimates of both the marine reflectance in the red spectral region (67 0 nm) and the Angstrom exponent, which links simple wavelengths ratios to r eflectance ratios. For case 1 waters, the optical properties of which are e ssentially dominated by planktonic pigments, the interrelations between mar ine reflectances and reflectance ratios at various wavelengths are derived from modelled calculations. For identified case 2 waters, where water const ituents other than planktonic pigments (i.e. dissolved organics and suspend ed sediments) dominate the water optical properties, the evaluation of mari ne reflectances is approximated by means of interpolated Angstrom exponent values computed over case 1 water pixels and of empirical relationships der ived from in situ measurements. The computation of chlorophyll-like pigment s is performed with algorithms based on blue/green (443-550 nm) reflectance ratios, for lower pigment concentration, or on green/green (520-550 nm) re flectance ratios, for higher pigment concentration. As for the case of atmo spheric corrections, the inter-relations between pigment concentration and reflectance ratios are model-derived for case 1 waters, and empirically det ermined for case 2 waters.