Abstract
A new model for the remote sensing of absorption coefficients of phytoplankton aph (λ) in oceanic and coastal waters is developed and tested with SeaWiFS and MODIS-Aqua data. The model is derived from a rela-tionship of the remote sensing reflectance ratio Rrs (670)/Rrs (490) and aph (490) and aph (670) (from large in-situ data sets). When compared with over 470 independent in-situ data sets, the model provides accurate retrievals of the aph (λ) across the visible spectrum, with mean relative error less than 8%, slope close to unity and R2 greater than 0.8. Further comparison of the SeaWiFS-derived aph (λ) with in-situ aph (λ) values gives similar and consistent results. The model when used for analysis of MODIS-Aqua imagery, provides more realistic values of the phytoplankton absorption coefficients capturing spatial structures of the massive algal blooms in surface waters of the Arabian Sea. These results demonstrate that the new algorithm works well for both the coastal and open ocean waters observed and suggest a potential of using remote sensing to provide knowledge on the shape of phytoplankton absorption spectra that are a requirement in many inverse models to estimate phytoplankton pigment concentrations and for input into bio-optical models that predict carbon fixation rates for the global ocean.
Highlights
Phytoplanktons play a critical role in the cycling of biogeochemical properties, and are responsible for much of the oxygen present in the Earth’s atmosphere through a process known as photosynthesis
The model when used for analysis of MODIS-Aqua imagery, provides more realistic values of the phytoplankton absorption coefficients capturing spatial structures of the massive algal blooms in surface waters of the Arabian Sea
These results demonstrate that the new algorithm works well for both the coastal and open ocean waters observed and suggest a potential of using remote sensing to provide knowledge on the shape of phytoplankton absorption spectra that are a requirement in many inverse models to estimate phytoplankton pigment concentrations and for input into bio-optical models that predict carbon fixation rates for the global ocean
Summary
Phytoplanktons play a critical role in the cycling of biogeochemical properties, and are responsible for much of the oxygen present in the Earth’s atmosphere through a process known as photosynthesis Their cumulative energy fixation in carbon compounds that account for approximately half of the world’s total primary productivity is the basis for the majority of oceanic food chains. The spectra of phytoplankton absorption (aph(λ)) vary widely both in terms of magnitude and spectral behaviour [9,10,11] in seawaters because of differences in phytoplankton community, cell size, and pigment packages among sites [11,12,13] For these reasons and because of the advent of remote sensing capabilities, there is increasing demand for a fundamental knowledge of the magnitude, range and sources of variability in phytoplankton optical properties in marine surface waters. Remote sensing offers the potential for synoptic assessment of pigment biomass and primary production, but this requires the ability to accurately estimate phytoplankton absorption coefficients from remotely measured signals using an appropriate optical model that has potential applications in ocean colour remote sensing
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