Opt Express. 2023 May 8;31(10):15966-15982. doi: 10.1364/OE.484390.
Diurnal monitoring of the Secchi-disk depth (SDD) of eutrophic lakes is the basic requirement to ensure domestic, industrial, and agricultural water use in surrounding cities. The retrieval of SDD in high frequency and longer observation period is the basic monitoring requirement to guarantee water environmental quality. Taking Lake Taihu as an example, the diurnal high-frequency observation (10 mins) data of the geostationary meteorological satellite sensor AHI/Himawari-8 were examined in this study. The results showed that the AHI normalized water-leaving radiance (L) product derived by the Shortwave-infrared atmospheric correction (SWIR-AC) algorithm was consistent with the in situ data, with determination coefficient (R) all larger than 0.86 and the mean absolute percentage deviation (MAPD) of 19.76%, 12.83%, 19.03% and 36.46% for the 460 nm, 510 nm, 640 nm and 860 nm bands, respectively. 510 nm and 640 nm bands showed more better consistency with in situ data in Lake Taihu. Therefore, an empirical SDD algorithm was established based on the AHI green (510 nm) and red (640 nm) bands. The SDD algorithm was verified by in situ data showed good performance with R of 0.81, RMSE of 5.91 cm, and MAPD of 20.67%. Based on the AHI data and established algorithm, diurnal high-frequency variation of the SDD in the Lake Taihu was investigated and the environmental factor (wind speed, turbidity degree, and photosynthetically active radiance) corresponding to diurnal SDD variation were discussed. This study should be helpful for studying diurnal high-dynamics physical-biogeochemical processes in eutrophication lake waters.
对富营养化湖泊的水色透明度（SDD）进行日监测是确保周边城市的居民用水、工业用水和农业用水的基本要求。高频次、长时间的 SDD 观测是保证水质的基本监测需求。本研究以太湖为例，检验了地球静止气象卫星传感器 AHI/Himawari-8 的日高频（10 分钟）观测数据。结果表明，经短波红外大气校正（SWIR-AC）算法反演得到的 AHI 归一化离水辐亮度（L）产品与现场数据一致，决定系数（R）均大于 0.86，460nm、510nm、640nm 和 860nm 波段的平均绝对百分比偏差（MAPD）分别为 19.76%、12.83%、19.03%和 36.46%。510nm 和 640nm 波段与太湖现场数据的一致性更好。因此，基于 AHI 的绿光（510nm）和红光（640nm）波段，建立了经验 SDD 算法。现场数据验证表明，SDD 算法具有较好的性能，R 为 0.81，RMSE 为 5.91cm，MAPD 为 20.67%。基于 AHI 数据和建立的算法，研究了太湖 SDD 的日高频变化，并讨论了与 SDD 日变化相对应的环境因子（风速、浑浊度和光合有效辐射）。本研究有助于研究富营养化湖泊水日内高动态的物理-生物地球化学过程。
