Retrieval of phytoplankton cell size from chlorophyll a specific absorption and scattering spectra of phytoplankton

Phytoplankton cell size is an important property that affects diverse ecological and biogeochemical processes, and analysis of the absorption and scattering spectra of phytoplankton can provide important information about phytoplankton size. In this study, an inversion method for extracting quantitative phytoplankton cell size data from these spectra was developed. This inversion method requires two inputs: chlorophyll a specific absorption and scattering spectra of phytoplankton. The average equivalent-volume spherical diameter (ESD_v) was calculated as the single size approximation for the log-normal particle size distribution (PSD) of the algal suspension. The performance of this method for retrieving cell size was assessed using the datasets from cultures of 12 phytoplankton species. The estimations of aλ and bλ for the phytoplankton population using ESD_v had mean error values of 5.8%–6.9% and 7.0%–10.6%, respectively, compared to the aλ and bλ for the phytoplankton populations using the log-normal PSD. The estimated values of C_iESD_v were in good agreement with the measurements, with r² 0.88 and relative root mean square error NRMSE 25.3%, and relatively good performances were also found for the retrieval of ESD_v with r² 0.78 and NRMSE 23.9%.