Global Retrieval of Phytoplankton Functional Types (PFTs) from OLCI and Merged Ocean Colour products
This collaborative AWI-ACRI-ST project funded by ACRI-ST focuses on retrieving global PFTs from Sentinel-3 OLCI data and merged ocean colour (CMEMS GlobColour) products, with integrated use of extensive in situ measurements from various cruises in different regions.
A previously empirical orthogonal functions based approach, developed only for certain ocean regions (Bracher et al. 2015), is now further extended to be used globally and can be applied to any satellite reflectance data set which covers spectral information of at least nine different spectral bands. For the algorithm development it requires input data including not only the satellite data but also a very large (about 12,000) globally distributed field data set on phytoplankton pigments. With data of only nine spectral bands from the merged ocean color products, it is possible to quantify chlorophyll a concentration of different PFTs on a large scale in both space and time. Climatological characteristics of the PFTs are also evaluated based on ten years of merged products (2002−2012; see Figure 1) through inter-comparisons with other existing satellite derived products on phytoplankton composition including phytoplankton size class (PSC), SynSenPFT, OC-PFT and PHYSAT. Preliminary experiment of the algorithm using eleven OLCI bands is applied to monthly OLCI products, showing comparable PFT distributions with those from the merged ocean color products, though the matchup data for OLCI are limited both in number and coverage. Within the framework of EU Copernicus Marine Environment Monitoring Service (CMEMS), the objective of this study is to ultimately deliver satellite global PFT products for long-term continuous observation which will be updated timely with upcoming OC data, for a comprehensive understanding of the variability of phytoplankton composition structure at a global or regional scale. These results are published in Xi et al. (2020).
Bracher A., Taylor B.B., Taylor M., Dinter T., Röttgers R., Steinmetz F. (2015) Using empirical orthogonal functions derived from remote sensing reflectance for the prediction of concentrations of phytoplankton pigments. Ocean Science 11: 139-158.
Xi, H., Losa, S.N., Mangin, A., Soppa, M.A., Garnesson, P., Demaria, J., Liu, Y., d’Andon, O.H.F., Bracher, A., 2020.Global retrieval of phytoplankton functional types based on empirical orthogonal functions using CMEMS GlobColour merged products and further extension to OLCI data, Remote Sensing of Environment, 240, 111704. doi:10.1016/j.rse.2020.111704
Figure 1:Ten-year mean distribution (July 2002–April 2012) of the chlorophyll a concentration for phytoplankton groups: (A) diatoms, (B) dinoflagellates, (C) haptophytes, and (D) green algae retrieved by EOF-based algorithm from CMEMS merged monthly Rrs (remote sensing reflectance) products at nine bands. Microscope photo of the representing species for each phytoplankton group is also shown on top right of each map.(Graphic: Hongyan Xi AWI)