Abstract

Values for the coefficients of absorption (a) and attenuation (c) obtained from AC-9 measurements in coccolithophore blooms do not provide satisfactory inputs for radiance transfer models. We have therefore modified the standard AC-9 scattering correction algorithm by including an extra term, F(λ, λ_r), which allows for possible wavelength dependence in the scattering phase function. We estimated the magnitude of F(λ, λ_r), which is unity in the standard algorithm, by adjusting the absorption and scattering values in Hydrolight radiance transfer calculations until the depth profiles of downward irradiance (E_d) and upward radiance (L_u) matched those measured in situ. The modified algorithm was tested with data from a phytoplankton bloom dominated by the coccolithophore Emiliania huxleyi, which occurred in the western English Channel in May 2001. In this paper, we only have sufficient data to adequately constrain the radiance transfer model in one wave band centered on 488 nm. A single value of F(λ, λ_r) = 1.4 was found to produce satisfactory agreement between modeled and observed profiles at four widely spaced stations within the bloom. Measurements of the ratio of backscattering (b_b) to total scattering (b) showed significant wavelength dependence at these stations.

© 2003 Optical Society of America

Optical modeling and measurements of a coccolithophore bloom

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