Radiative transfer model for natural fluorescence of phytoplankton in the ocean

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

Howard R. Gordon, Committee Chair


An analytic model (AM) was developed to solve the radiative transfer equation for the natural fluorescence of phytoplankton in a horizontally homogeneous ocean with depth-dependent inherent optical properties using the quasi-single scattering approximation. A standard Monte Carlo simulation code (MC) for the underwater light field was modified to include fluorescent emission. Using the MC results for the incident scalar irradiance $E\sb{o}(z,\lambda\sb{e}),$ given the absorption coefficient $a(z,\lambda\sb{e})$ at an exciting wavelength $\lambda\sb{e},$ and the downwelling irradiance attenuation coefficient $K\sb{d}(z,\lambda\sb{f})$ at the fluorescent wavelength $\lambda\sb{f}$ as experimental data, the AM-computed values for fluorescent upwelling and downwelling irradiances, $E\sb{u}(z,\lambda\sb{e},\lambda\sb{f})$ and $E\sb{d}(z,\lambda\sb{e},\lambda\sb{f}),$ and upwelling and downwelling scalar irradiances, $E\sb{ou}(z,\lambda\sb{e},\lambda\sb{f})$ and $E\sb{od}(z,\lambda\sb{e},\lambda\sb{f}),$ reproduce the MC simulations at all depths. Using this model, the validity of the mean chlorophyll a absorption approximation has been examined and the vertical distribution of the ratio of total fluorescent nadir radiance $L\sb{ut}(z,685)$ at $\lambda$ = 685 nm to photosynthetically available radiation $E\sb{o}(z,PAR)$ has been calculated. The results were compared with observed data to estimate the fluorescence quantum efficiency of chlorophyll a for several stations with different chlorophyll a concentration profiles.


Biology, Oceanography; Biophysics, General

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