Ocean color products from hyperspectral satellite sensor SCIAMACHY compared to products from the multispectral sensors MERIS, MODIS and SeaWiFS.

Astrid.Bracher [ at ] awi.de


Quantitative distributions of major functional PFTs of the world ocean improve the understanding of the role of marine phytoplankton in the global marine ecosystem and biogeochemical cycles. Chl-a fluorescence gives insight on the health of phytoplankton and is related to phytoplankton biomass. In this study, global ocean color satellite products of different dominant phytoplankton functional types' (PFTs') biomass and chlorophyll fluorescence retrieved from hyperspectral satellite data using Differential Optical Absorption Spectroscopy (DOAS) are presented. Global biomass distributions from 2002 -2010 of different dominant PFTs (diatoms, cyanobacteria, coccolithophores, dinoflagellates) are derived with PhytoDOAS, the currently specialized method of DOAS for deriving chl-a of PFTs from satellite data of SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) on ENVISAT (details in Bracher et al. BG 2009, Sadeghi et al. OSD 2011). Results of the global maps of PFT distribution are validated with global PFT data derived from using Hirata et al. (2011) approach of parameterizing satellite chl-a from Globcolour with collocated HPLC pigment data. In addition, SCIAMACHY monthly mean data of coccolithophore biomass in three selected oceanic regions were compared to related satellite products, including the total surface phytoplankton, i.e., total chlorophyll-a (from GlobColour merged data) and the particulate inorganic carbon (from MODIS-Aqua). The DOAS method was also adapted to detect successfully globally the filling-in of Fraunhofer Lines caused by chlorophyll fluorescence in the backscattered SCIAMACHY spectra and compared to data of fluorescence-line-height from MODIS and MERIS. The results suggest that DOAS is a valid method for retrieving PFTs and chlorophyll fluorescence from hyper-spectral measurements. Overall, DOAS products are much less dependent on a priori information than common multi-spectal ocean colour products which result from empirical and semi-analytical methods. In addition, the DOAS technique has the advantage to overcome problems with an accurate atmospheric correction encountered for the traditional multi-spectral ocean color products because only the differential signals of both atmospheric and oceanic absorbers are fitted while all other (broad-band) absorption and scattering processes are successfully approximated with an low order polynomial. Although current hyperspectral sensors have poor spatial resolution (>30kmx30km), they are useful for the verification and improvement of the high spatially resolved multi-spectral ocean color products. Future applications of PhytoDOAS retrieval to other hyperspectral sensors and its synergistic use with information gained from multispectral ocean color sensors are proposed.

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Sentinel-3 OLCI/SLSTR & MERIS/(A)ATSR Workshop, 15 Oct 2012 - 19 Oct 2012, ESA-ESRIN, Frascati, Italy.
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Bracher, A. , Dinter, T. , Sadeghi, A. , Wolanin, A. , Altenburg Soppa, M. , Taylor, B. , Rozanov, V. , Vountas, M. , Röttgers, R. and Peeken, I. (2012): Ocean color products from hyperspectral satellite sensor SCIAMACHY compared to products from the multispectral sensors MERIS, MODIS and SeaWiFS. , Sentinel-3 OLCI/SLSTR & MERIS/(A)ATSR Workshop, ESA-ESRIN, Frascati, Italy, 15 October 2012 - 19 October 2012 .

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