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Fig. 1. (A) Absorption coefficient normalized to Chl a, a ph, for different species of diatoms, Bacillariophyceae, and dinoflagellates, Dinophyceae. Green dashed line is an absorption spectrum for Chl a extracted in methanol and red dashed line is for the peridinin–chlorophyll–protein complex (scaled for figure) to illustrate the absorption due to accessory pigments. (B) Median absorption spectra normalized to Chl a for different phytoplankton communities (Stramski et al. 2001).
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Fig. 2. (A) Backscattering estimated for phytoplankton concentrations of 30 mg Chl a m23 for each taxon (Stramski et al. 2001), as defined in Fig. 1. (B) Remote sensing reflectance, Rrs, measured from a variety of dinoflagellate red tides along the California coast. Lingulodinium polyedra spectrum provided courtesy of G. Chang. (C) Water-leaving radiance, Lw, modeled for dense phytoplankton bloom conditions (30 mg Chl a m23) from a variety of phytoplankton taxa. (D) Data from panel (C) shown as Rrs.
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Fig. 3. Response of the three cone classes (short, middle, and long) in the human eye to different wavelengths of light (scaled to the same range, Livingstone 2002). The bottom color spectrum indicates the color associated with individual wavelengths of light. The gray bars represent the wavelengths used by the Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color sensor.
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Fig. 4. (A) Particulate absorption coefficient for a diatom showing the increase in absorption with increasing concentration. The wavelength at which absorption due to phytoplankton and that due to pure water (Pope and Fry 1997) intersect represents the minimum in absorption and the maximum or peak reflectance. (B) Spectral variability in water-leaving radiance (Lw) modeled for a diatom bloom with increasing Chl a concentrations (2, 5, 10, 15, 20, 30, 40, 50 mg m23). Dotted line shows the peak wavelengths. (C) Spectra from panel (B) normalized to peak water-leaving radiance. The corresponding color associated with each spectrum is shown in the results for Bacillariophyceae in Fig. 5A.
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Fig. 5. (A) Color of the sea surface as a function of surface biomass concentration (Chl a used as a proxy) for different phytoplankton taxa. Color was modeled from water-leaving radiance using the CIE color matching functions and mean absorption and backscattering properties for each taxa. (B) The chromaticity coordinates for a selection of three algal taxa are shown on a CIE chromaticity diagram (Kelly 1943) as Chl a increases from 2 mg m23 (lower left points) to 50 mg m23 (upper right points). For clarity, the color of each symbol corresponds to the color presented for that algal group in panel (A).
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Fig. 6. Sensitivity analysis of particulate absorption, backscattering, and solar zenith angle (SZA) on modeled upwelling radiance at the sea surface and resulting color. Each column represents a different modeling scenario (1–4) used in the hydrolight radiative transfer model (Mobley 1994). The first row of panels provides the phytoplankton absorption properties, aph, for each scenario. The second row provides the particulate backscattering, bbp. The upwelling radiance spectra, Lu, modeled at the sea surface using the absorption and backscattering properties is shown in the third row of panels. Note that the scale for panel O is four times that of panels C, G, and K. The fourth row is the Lu spectra normalized to the peak Lu and represents the relative contributions of radiance in each wavelength. The bottom color bars show the resulting colors modeled from each spectrum.
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Fig. 7. Relative reflectance of unicellular algal cultures captured onto GF/F filters increases strongly from 680 to 710 nm, producing a red edge typical of photosynthetic tissues. The reflectance spectrum from a terrestrial aspen leaf (Hall et al. 1991) is shown for comparison. Spectra are normalized to reflectance at 800 nm and do not contain a solar-stimulated fluorescence peak centered at 683 nm.
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Fig. 8. (A) Mass-specific particulate absorption coefficients and (B) scattering coefficients for various mineral types (Ahn 1990). (C) Remote sensing reflectance spectra, Rrs, and (D) waterleaving radiance spectra, Lw, modeled using the optical properties for a mineral concentration of 20 g m23. Absorption and reflectance spectra for waters dominated by colored dissolved organic matter (CDOM) are shown for comparison (scaled to fit).
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Fig. 9. Color of the sea surface as a function of increasing concentrations of (A) colored dissolved organic matter (CDOM), shown as absorption at 412 nm, and CDOM with the addition of nonabsorbing backscattering matter, and (B) four different types of minerals. (C) Satellite image of the confluence of the black waters of the Rio Negro in the north and the sediment-laden Rio Solimoes to the southeast in Manuas, Brazil. Multi-angle imaging spectroradiometer (MISR) image obtained from the NASA Goddard Earth Sciences Data and Information Services Center Web site (Acker and Kempler 2004). (D) Photo showing the water color of a shallow inlet in Western Australia containing high CDOM concentrations (courtesy of G. Chang). White kayak paddle is shown for perspective.
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