Journal of East China Normal University(Natural Science) ›› 2024, Vol. 2024 ›› Issue (4): 123-136.doi: 10.3969/j.issn.1000-5641.2024.04.012

• Remote Sensing and Geographic Information System • Previous Articles    

Machine learning-based remote sensing retrievals of dissolved organic carbon in the Yangtze River Estuary

Hao CHEN1, Xianqiang HE2, Run LI1, Fang CAO1,*()   

  1. 1. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China
    2. State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
  • Received:2023-03-22 Accepted:2023-04-18 Online:2024-07-25 Published:2024-07-23
  • Contact: Fang CAO E-mail:fcao@sklec.ecnu.edu.cn

Abstract:

Dissolved organic carbon (DOC) is the largest reservoir of active organic matter in the ocean. Accurate characterization of the spatial and temporal patterns of DOC in large-river estuaries and neighboring coastal margins will help improve our understanding of biogeochemical processes and the fate of fluvial DOC across the estuary−coastal ocean continuum. By retrieving the absorption properties of colored dissolved organic matter (CDOM) in the dissolved organic matter (DOM) pool using machine learning models, and based on the correlation between CDOM absorption and DOC concentrations, we developed an ocean DOC algorithm for the GOCI satellite. The results indicated that the Nu-Supporting Vector Regression model performed best in retrieving CDOM absorption properties, with mean absolute percent differences (MAPD) of 32% and 8.6% for the CDOM absorption coefficient at 300 nm (aCDOM(300)) and CDOM spectral slope over the wavelength range of 275 ~ 295 nm (S275–295). Estimates of DOC concentrations based on the seasonal linear relationship between aCDOM(300) and DOC were achieved with high retrieval accuracy, with MAPD of 11% and 14% for the training dataset using field measurements and validation datasets on satellite platforms, respectively. Application of the DOC algorithm to GOCI satellite imagery revealed that DOC levels varied dramatically at both seasonal and hourly scales. Elevated surface DOC concentrations were largely associated with summer and lower DOC concentrations in winter as a result of seasonal cycles of Yangtze River discharges. The DOC also changed rapidly on an hourly scale due to the influence of the tide and local wind regimes. This study provides a useful method to improve our understanding of DOC dynamics and their environmental controls across the estuarine −coastal ocean continuum.

Key words: GOCI (geostationary ocean color imager), colored dissolved organic matter, machine learning, the Yangtze River Estuary, dissolved organic carbon

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