Chlorella vulgaris measurements using full-spectrum goniometer for optically complex inland water monitoring

Rising environmental stressors, including climate change, nutrient loading, pollution, and anthropogenic impacts, have made the continuous monitoring of lake water quality increasingly essential. While in situ methods offer high precision, satellite-based remote sensing is essential for capturing large-scale, long-term changes and accessing remote or extreme environments. To complement these approaches, we developed a cost-effective in situ optical measurement system specifically designed for optically complex inland waters. The instrument enables detailed optical characterization across scattering angles from 0 degrees to 160 degrees and wavelengths between 423 and 728 nm, covering both visible and near-infrared regions. Initial validation was performed using monocultures of Chlorella vulgaris, a well-established model organism for chlorophyll-a optical studies. As a result of laboratory measurements of C. vulgaris monocultures using a spectral goniometer, forward and backward scattering profiles, polarization characteristics, three-dimensional patterns, volume scattering functions, and radiant intensities at 90 degrees across Sentinel-3 OLCI bands toward density changes were modeled. The results confirmed Mie scattering dominance in line with the theoretical expectations. Overall, the developed full-spectrum goniometer can serve as a reliable and practical tool for in situ optical monitoring.