| Liu Xianfu,Meng Xuejiao,Wang Xiaoyong,Bi Dayong,Chen Lei,Lou Quansheng. 2020. Using a semi-analytical model to retrieve Secchi depth in coastal and estuarine waters. Acta Oceanologica Sinica, 39(8):103－112 |
| Using a semi-analytical model to retrieve Secchi depth in coastal and estuarine waters |
| 半分析模型在近岸及河口水体透明度反演应用研究 |
| Received:September 30, 2019 |
| DOI：10.1007/s13131-020-1620-2 |
| Key words:Secchi depth water quality coastal and estuarine waters semi-analytical model remote sensing Landsat-8 |
| 中文关键词: 透明度 水质 近岸与河口水体 半分析模型 遥感 Landsat-8 |
| 基金项目:The National Natural Science Foundation of China under contract No. 61527810; the Marine Science and Technology Fund from Director of South China Sea Branch, State Oceanic Administration of China under contract No. 180101; the Key Laboratory Open Project Fund of Technology and Application for Safeguarding of Marine Rights and Interests, State Oceanic Administration of China under contract No. 1720. |
| Author Name | Affiliation | E-mail | | Liu Xianfu | South China Sea Institute of Planning and Environmental Research, State Oceanic Administration, Guangzhou 510300, China | | | Meng Xuejiao | Shanwei Marine Environmental Monitoring Center Station, State Oceanic Administration, Shanwei 516600, China | amymong@qq.com | | Wang Xiaoyong | National Ocean Technology Center, State Oceanic Administration, Tianjin 300112, China | | | Bi Dayong | National Ocean Technology Center, State Oceanic Administration, Tianjin 300112, China | | | Chen Lei | South China Sea Institute of Planning and Environmental Research, State Oceanic Administration, Guangzhou 510300, China | | | Lou Quansheng | Environmental Monitoring Center of South China Sea, State Oceanic Administration, Guangzhou 510300, China | |
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| Abstract: |
| Secchi depth (SD, m) is a direct and intuitive measure of water’s transparency, which is also an indicator of water quality. In 2015, a semi-analytical model was developed to derive SD from remote sensing reflectance, thus able to provide maps of water’s transparency in satellite images. Here an in-situ dataset (338 stations) is used to evaluate its potential ability to monitor water quality in the coastal and estuarine waters, with measurements covering the Zhujiang (Pearl) River Estuary, the Yellow Sea and the East China Sea where measured SD values span a range of 0.2–21.0 m. As a preliminary validation result, according to the whole dataset, the unbiased percent difference (UPD) between estimated and measured SD is 23.3% (N=338, R2=0.89), with about 60% of stations in the dataset having relative difference (RD)≤20%, over 80% of stations having RD≤40%. Furthermore, by excluding the field data which with relatively larger uncertainties, the semi-analytical model yielded the UPD of 17.7% (N=132, R2=0.92) with SD range of 0.2–11.0 m. In addition, the semi-analytical model was applied to Landsat-8 images in the Zhujiang River Estuary, and retrieved high-quality mapping and reliable spatial-temporal patterns of water clarity. Taking into account the uncertainties associated with both field measurements and satellite data processing, and that there were no tuning of the semi-analytical model for these regions, these findings indicate highly robust retrieval of SD from spectral techniques for such turbid coastal and estuarine waters. The results suggest it is now possible to routinely monitor coastal water transparency or visibility at high-spatial resolutions from measurements, like Landsat-8 and Sentinel-2 and newly launched Gaofen-5. |
| 中文摘要: |
| 透明度是水体透明状况的直观表征，也是评价水质的重要指标。2015年研究出了一种半分析模型，通过遥感反射率反演水体透明度，为后续利用卫星影像获取水体透明度提供了有力手段。为评估此半分析模型在近岸及河口水体中的适用性，本论文利用中国珠江口、黄海和东海海域现场实测的338个站点数据（透明度范围为0.2 ~ 21.0m），对半分析模型的反演精度进行了检验。结果发现，现场实测水体透明度和模型反演值的相关系数（R2）为0.89，相对偏差为23.3%，均方根误差为1.70m，其中约60%的站点实测值和反演值之间相对偏差不大于20%，约80%的站点实测值和反演值之间相对偏差不大于40%。当剔除了存在较大不确定性的现场测量数据，仅利用实测透明度在0.2 ~ 11.0m之间的132个站点数据进行进一步验证时，得到了更高的模型反演精度（R2为0.92，相对偏差为17.7%，均方根误差为0.85m）。此外，本文还将半分析模型应用到Landsat-8卫星影像中，获取了我国珠江口高分辨率的透明度时空分布信息。虽然现场测量和卫星影像处理过程会存在不确定性，而在利用模型反演水色透明度过程也没有针对应用区域进行模型参数调整，本文对半分析模型的反演精度验证仍然取得了较好的结果，充分表明通过光谱技术手段来获取水色透明度是值得信赖的。因此，建议在今后的工作中，可大力应用Landsat-8、哨兵-2以及我国最近成功发射的高分-5号等卫星影像，获取高分辨率的水体透明度信息，应用到我国近海业务化水质监测之中。 |
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