Quasi-Invariance of Scattering Properties of Multicellular Cyanobacterial Aggregates

The radiative/scattering properties of cyanobacterial aggregates are crucial for understanding microalgal cultivation. This study analyzed the scattering matrix elements and cross-sections of cyanobacterial aggregates using the discrete dipole approximation (DDA) method. A stochastic random walk approach was adopted to generate a force-biased packing model for multicellular filamentous cyanobacterial aggregates. The effects of the shape and size of multicellular cyanobacterial aggregates on their scattering properties were investigated in this work. The possibility of invariance in the scattering properties of cyanobacterial aggregates was explored. The invariance interpretation intuitively represented the radiative property characteristics of the aggregates. The presented results show that the ratios of the matrix elements of cyanobacterial aggregates are nearly shape-, size-, and wavelength-invariant. The extinction and absorption cross-sections (EACSs) per unit volume exhibited shape and approximate size invariance for cyanobacterial aggregates, respectively. The absorption cross-section of aggregates is not merely a volumetric phenomenon for aggregates that exceed a certain size. Furthermore, the absorption cross-sections per unit volume are independent of the volumetric distribution of the microalgae cells. The invariance interpretation presents crucial characteristics of the scattering properties of cyanobacterial aggregates. The existence of invariance greatly improves our understanding of the scattering properties of microalgal aggregates. The scattering properties of microalgal aggregates are the most critical aspects of light propagation in the design, optimization, and operation of photobioreactors.