[A-CG36] Satellite Earth Environment Observation

[ACG36-P03] Multi-Satellite Data Analysis of Spatiotemporal Variations in Water Quality in I-Lan Bay

*Jiun-Yu Yang¹, Po-Chun Hsu¹ (1.Center for Space and Remote Sensing Research, National Central University)

Keywords:Water Quality Index, Apparent Visible Wavelength, Chlorophyll, Kd490

I-Lan Bay (121.85-122°E, 24.6-25°N), located at the northeast corner of Taiwan at the junction of the Kuroshio Current (KC) and the East China Sea, receives water from the Lan Yang River, the offshore KC, and coastal waters. The flow field in I-Lan Bay is determined by the northeastward counter-current of Taiwan, with the interaction between the KC and tidal flows playing a crucial role. This study examines water quality characteristics such as chlorophyll concentration, Kd490, and the Apparent Visible Wavelength (AVW), which is calculated as a weighted average from remote sensing reflectance (R_rs) data between wavelengths of 400 to 700 nanometers. AVW values, represented as a wavelength, indicate the water body's absorption of light across different wavelengths. Data for this study were derived from three types of instruments on six different satellites, including MODIS on AQUA and TERRA, VIIRS on SNPP and NOAA-20, and OLCI on Sentinel-3, spanning Level-3 monthly average data from 2019 to 2022. The study analyzes seasonal variations in water quality within I-Lan Bay through environmental factors such as runoff from the Lan Yang River and precipitation in the I-Lan area. Results show a correlation of 0.89 between Lan Yang River runoff and I-Lan area precipitation, and a correlation of 0.71 between Lan Yang River runoff and chlorophyll concentration within the bay, with a precipitation correlation of 0.7. Peak chlorophyll concentrations occur in October and November, aligning with I-Lan's rainy season. Spatial distribution of water quality in I-Lan Bay reveals AVW values exceeding 500nm near the river mouth, indicating green water, while the northern and southwestern parts of the bay, influenced by the Northeast Taiwan Counter Current (NETCC) and the KC, have AVW values below 475nm, indicating blue water. In other areas of the bay, AVW values range between 475-500nm, suggesting cyan water. Finally, by examining changes in the flow field, we found that the distribution of water quality within I-Lan Bay is primarily controlled by tidal currents, with occasional influence from the NETCC flowing in from the north.