Diel variations of the attenuation, backscattering and absorption coefficients of four phytoplankton species and comparison with spherical, coated spherical and hexahedral particle optical models

Assessing the Impact of a Two-Layered Spherical Geometry of Phytoplankton Cells on the Bulk Backscattering Ratio of Marine Particulate Matter

“…The variation of b θ a bp due to structural heterogeneity of phytoplankton cells is evaluated using the relative absolute difference calculated between the homogeneous reference cases (named x in Equation (13)) and oligotrophic, phytoplankton bloom or coastal-like water bodies (named y in Equation (13)): Even if the numerical relative abundance of phytoplankton is very small for the oligotrophic-like water body (=8.4 × 10 −3 %), the structural heterogeneity increases the b θ a bp value by 58% compared to the homogeneous case ("Homogeneous reference case 1"). This is consistent with previous studies showing the large contribution of coated spheres to the backscattering signal [15,16,18,19,22,44]. The value of ∆ calculated between the oligotrophic-like and phytoplankton bloom water bodies is smaller (=22% at ξ = 4) even ifñ i is different (9.93 × 10 −4 for oligotrophic-like against 1.36 × 10 −3 for phytoplankton bloom).…”

“…The real refractive index of the chloroplast and the relative volume of the chloroplast are key parameters impacting the backscattering efficiency of phytoplankton cells. This was recently confirmed by two studies where measurements of light scattering by phytoplankton cultures were well reproduced by the two-sphere model [15,16]. For these reasons, in this study, phytoplankton optical properties have been simulated considering a two-layered sphere model.…”

“…Indeed, the structural heterogeneity and inner complexity of phytoplankton cells (gas vacuoles, chloroplast, silica wall, etc.) explain why the measured backscattering signal is higher than predicted by the Lorentz-Mie theory for homogeneous spheres [11][12][13][14][15][16][17][18][19][20]. The underestimation of b bp by homogeneous spheres may explain the fact that in situ observations of backscattering are significantly higher than theoretical simulations [21][22][23].…”

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

“…Other efforts to account for particle non-sphericity in RT simulations of underwater light are described by Gordon et al (2009) and Gordon (2011) for the scattering properties of detached coccoliths, by Zhai et al (2013) and Bi and Yang (2015) for the scattering properties of whole coccolithophores, and by Fournier and Neukermans (2017) and Neukermans and Fournier (2018) for the scattering properties of both detached coccoliths and whole coccolithophores. In addition, Organelli et al (2018) started using coated spheres in RT computations to force closure with underwater light particulate backscattering and attenuation measurements, whereas Poulin et al (2018) compared the performance of coated spheres and hexahedral shapes in closure studies of phytoplankton cultures.…”

“…We note at this point that while each of the abovementioned approaches for hydrosol scattering (i.e., internal structure of plankton, non-spherical shape of marine particulates, submicron-sized marine particulates, VSF decomposition) may provide a reasonable or partial solution for the "missing particulate backscattering enigma" (see discussions in Stramski et al, 2004;Organelli et al, 2018;Poulin et al, 2018), a particle model that incorporates all these approaches to study their combined impact on backscattering remains an outstanding topic of research. Such a model could validate, or lead to adjustments of, parameter choices made for each approach such as refractive index and shape distributions of marine particles.…”