[A-HW18] Hydrology & Water Environment

[AHW18-15] Determination of Effective Wavelength to Estimate Water Contaminant Concentration by Using Normalized Difference Spectral Index (NDSI)

*Ahmad Shaqeer Mohamed Thaheer¹, Yukihiro Takahashi¹ (1.Department of Cosmosciences, Faculty of Science, Hokkaido University)

Keywords:Contaminant Concentration, Polarization, Water Waves, Spectral Measurement

Assessing pollution in inland water bodies is crucial for ensuring water security and understanding its impact on outflows such as the ocean. Southeast Asian urban areas, like Malaysia, are facing significant pollution challenges. Researchers often use in-situ measurements based on the Water Quality Index (WQI) methodology, but its limitations become apparent when applied on a large scale. Remote sensing tools like satellites and drones offer a promising solution for water monitoring, enabling wide-area observations at frequent intervals. However, measuring light reflection on the water surface, often rippled by small wind-driven waves, poses a significant obstacle. Researchers have explored spectral reflectance with polarization at visible and near-infrared wavelengths to address this challenge. The intensity of sun glints is mainly dependent on the water surface roughness and solar elevation angle. Under calm conditions, the number of sunglints decreases. In the laboratory, spectral reflectance was measured for each contaminant (chlorophyll and soil) concentration by simulating artificial waves on the water surface using a wave generator. The effective wavelength combination was determined by calculating the normalized difference spectral index (NDSI) and correlation coefficient for each corresponding wavelength. Finally, the mixed condition was estimated at different camera angles using the selected wavelength. An alternative measurement in the future, whether for drones, satellites, or in-situ measurements for assessing water contaminant concentration, is provided by this work.