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Ocean Colour Portal

Ocean colour remote sensing allows the study of the optical properties of the oceans and the biology of the marine ecosystems. The right-hand links lead to images of chlorophyll a maps for the European seas and the global ocean, or to the MERSEA Thematic Portal.


European Seas Regional Data Sets

The Global Environment Monitoring Unit is maintaining an archive of ocean colour derived products for the European seas, over the geographical domain 40W-55E, 10N-80N (see domain on the right). This site shows maps of chlorophyll a concentration for specific regions covering the European Atlantic sector from the Arctic to the Cape Verde Islands, the North Sea, Baltic Sea, Mediterranean Sea, Black Sea and Caspian Sea. The time series contains daily, 8-day and monthly maps derived from SeaWiFS and MODIS for the period Sep. 1997 to present. These maps have an approximate resolution of 2-km and are obtained after processing of all top-of-atmosphere full resolution imagery available for the domain. The processor used for the development of the archive is SeaDAS version 4.8.

The archive contains several categories of products:

  • aerosol description (optical thickness and Ångström exponent),
  • ocean surface apparent optical properties: normalized water leaving radiances Lwn, diffuse attenuation coefficient Kd,
  • concentrations of optically significant constituents: Chlorophyll a, total suspended matter,
  • inherent optical properties: absorption, backscattering,
  • photosynthetically available radiation (PAR, for SeaWiFS only).

Global Data Sets

The GEM also maintains a global archive of ocean colour derived data sets, based on SeaWiFS and MODIS. Emphasis is given for the study of the global oceans with monthly maps of aerosol optical thickness, normalized water leaving radiances, diffuse attenuation coefficient, chlorophyll a concentration and PAR. Moreover, chlorophyll a and PAR time series are used to compute global primary production with a depth- and wavelength-resolved primary productivity model (see example of annual PP estimate on the right).


Northern Adriatic Sea validation time series

As a product of reference for calibration purposes and for comparison with the outputs of its own algorithms, the Unit keeps an ocean colour data archive focused on the Northern Adriatic Sea, where the Acqua Alta Oceanographic Tower measurement site is located. This web site shows the SeaWiFS series for this location processed with the SeaDAS software package.

Selected references for validation studies:

  • Mélin, F., Zibordi, G., Berthon, J.-F.: Assessment of SeaWiFS atmospheric and marine products for the Northern Adriatic Sea. IEEE Trans. Geosci. Remote Sens., 41, 548-558, 2003.
  • Mélin, F., Berthon, J.-F., Zibordi, G.: Assessment of apparent and inherent optical properties derived from SeaWiFS with field data. Remote Sens. Environ., 97, 540-553, 2005.
  • Zibordi, G., Mélin, F., Berthon, J.-F.: Comparison of SeaWiFS, MODIS and MERIS radiometric products at a coastal site. Geophys. Res. Lett., 33, L06617, 10.1029/2006GL025778, 2006.
  • Zibordi, G., Mélin, F., Berthon, J.-F.: A time series of above-water radiometric measurements for coastal water monitoring and remote sensing product validation. IEEE Geosci. Remote Sens. Lett., 3, 120-124, 10.1109/LGRS.2005.858486, 2006.


Acknowledgements

The Ocean Biology Processing Group of NASA is acknowledged for the distribution of Level-1 to Level-3 SeaWiFS and MODIS products, and for the availability of SeaDAS and the associated support.