Radiation characteristics of microalgae for different aggregation states: a case of Scenedesmus obliquus

The aggregation state of microalgae during their growth process has a significant impact on their optical radiation characteristics. This article takes Scenedesmus obliquus as an example and proposes a novel cell construction method that comprehensively considers the complex multi-component structure of microalgae. Three different models, namely single growth, paired growth, and four aggregation growth are established for microalgae cells with different aggregation states. The DDA (Discrete Dipole Approximation) method is used for theoretical calculations and compared with experimental data for verification. Compared with the models of Scenedesmus obliquus in three aggregation states (single, paired, and four growth), the weighted average calculation effectively reduced the theoretical calculation deviation by 15 % - 200 % through the weighted average of the results. The results show that the microalgae cell model considering multi-component complex structures has high computational accuracy and is in good agreement with experimental results. In addition, when considering the effect of microalgae cell aggregation, the absorption cross-section and scattering cross-section are greatly affected, while the scattering phase function is less affected by aggregation. The values of absorption cross-section and scattering cross-section grow in a multiplicative manner with the increase of aggregation numbers.