Ding Xiaosong, He Xianqiang, Bai Yan, Zhu Qiankun, Gong Fang, Li Hao, Li Jiajia
Opt Express. 2020 Sep 14;28(19):27387-27404. doi: 10.1364/OE.401323.
Driven by tidal forcing and terrestrial inputs, suspended particulate matter (SPM) in shallow coastal waters usually shows high-frequency dynamics. Although specific geostationary satellite ocean color sensors such as the geostationary ocean color imager (GOCI) can observe SPM hourly eight times in a day from morning to afternoon, it cannot cover the whole semi-diurnal tidal period (∼12 h), and an hourly frequency may be insufficient to witness rapid changes in SPM in highly dynamic coastal waters. In this study, taking the Yangtze River Estuary as an example, we examined the ability of the geostationary meteorological satellite sensor AHI/Himawari-8 to monitor tidal period SPM dynamics with 10-min frequency. Results showed that the normalized water-leaving radiance (Lwn) retrieved by the AHI was consistent with the in-situ data from both cruise- and tower-based measurements. Specifically, AHI-retrieved Lwn was consistent with the in-situ cruise values, with mean relative errors (MREs) of 19.58%, 16.43%, 18.74%, and 26.64% for the 460, 510, 640, and 860 nm bands, respectively, and determination coefficients (R) larger than 0.89. Both AHI-retrieved and tower-measured Lwn also showed good agreement, with R values larger than 0.75 and MERs of 14.38%, 12.42%, 18.16%, and 18.89% for 460, 510, 640, and 860 nm, respectively. Moreover, AHI-retrieved Lwn values were consistent with the GOCI hourly results in both magnitude and spatial distribution patterns, indicating that the AHI can monitor ocean color in coastal waters, despite not being a dedicated ocean color sensor. Compared to the 8 h of SPM observations by the GOCI, the AHI was able to monitor SPM dynamics for up to 12 h from early morning to late afternoon covering the whole semi-diurnal tidal period. In addition, the high-frequency 10-min monitoring by the AHI revealed the minute-level dynamics of SPM in the Yangtze River Estuary (with SPM variation amplitude found to double over 1 h), which were impossible to capture based on the hourly GOCI observations.
在潮汐力和陆地输入的驱动下，浅海沿岸水域的悬浮颗粒物（SPM）通常呈现高频动态变化。尽管像静止海洋彩色成像仪（GOCI）这样的特定地球静止卫星海洋颜色传感器能够在一天中从上午到下午每小时对SPM进行8次观测，但它无法覆盖整个半日潮周期（约12小时），而且每小时的观测频率可能不足以捕捉高动态沿岸水域中SPM的快速变化。在本研究中，以长江口为例，我们检验了地球静止气象卫星传感器先进 Himawari 8号成像仪（AHI/Himawari-8）以10分钟频率监测潮周期SPM动态变化的能力。结果表明，AHI反演的归一化离水辐射率（Lwn）与基于航次和铁塔测量的现场数据一致。具体而言，AHI反演的Lwn与现场航次测量值一致，在460、510、640和860纳米波段的平均相对误差（MRE）分别为19.58%、16.43%、18.74%和26.64%，决定系数（R）大于0.89。AHI反演的Lwn和铁塔测量的Lwn也显示出良好的一致性，在460、510、640和860纳米波段的R值大于0.75，平均误差率（MER）分别为14.38%、12.42%、18.16%和18.89%。此外，AHI反演的Lwn值在大小和空间分布模式上与GOCI每小时的结果一致，这表明AHI尽管不是专门的海洋颜色传感器，但也能够监测沿岸水域的海洋颜色。与GOCI对SPM的8小时观测相比，AHI能够从清晨到傍晚长达12小时监测SPM动态变化，覆盖了整个半日潮周期。此外，AHI每10分钟的高频监测揭示了长江口SPM的分钟级动态变化（发现SPM变化幅度在1小时内翻倍），这是基于GOCI每小时的观测无法捕捉到的。
