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Satellite ocean colour missions require a standardextraterrestrial solar irradiance spectrum in the visible and near-infrared(NIR) for use in the process of radiometric calibration, atmosphericcorrection and normalization of water-leaving radiances from in-situmeasurements. There are numerous solar irradiance spectra (or models)currently in use within the ocean colour community and related domains.However, these irradiance spectra, constructed from single and/or multiplemeasurements sets or models, have noticeable differences – ranging fromabout ±1% in the NIR to ±6% in the short wavelength region(ultraviolet and blue) – caused primarily by the variation in the solaractivity and uncertainties in experimental data from different instruments.Such differences between the applied solar irradiance spectra may have quiteimportant consequences in reconciliation, comparison and validation of theproducts resulting from different ocean colour instruments. Thus, it isprudent to examine the model-to-model differences and ascertain anappropriate solar irradiance spectrum for use in future ocean colourresearch and validation purposes. This study first describes the processeswhich generally require the application of a solar irradiance spectrum, andthen investigates the eight solar irradiance spectra (widely in use withinthe remote sensing community) selected on the basis of the followingcriteria: minimum spectral range of 350–1200 nm with adequate spectralresolution, completely or mostly based on direct measurements, minimal errorrange, intercomparison with other experiments and update of data. Thedifferences in these spectra in absolute terms and in the SeaWiFS andMERIS in-band irradiances and their consequences on the retrieval algorithmsof chlorophyll and suspended sediment are analyzed. Based on these detailedanalyses, this study puts forward the solar irradiance spectrum mostappropriate for all aspects of research, calibration and validation in oceancolour remote sensing. For an improved approximation of the extraterrestrialsolar spectrum in the ultraviolet-NIR domain this study also proposes a newsolar constant value determined from space-borne measurements of the lastthree decades

Reference solar irradiance spectra and consequences of their disparities in remote sensing of the ocean colour