用深度学习从光谱数据预测河口硝酸盐，助力珊瑚礁保护
Hyperspectral in situ remote sensing of water surface nitrate in the Fitzroy River estuary, Queensland, Australia, using deep learning
- 结合高光谱反射率与盐度，用深度学习建模硝酸盐浓度
- 预测结果与实测值相关性达R²=0.86，误差仅0.03 mg/L
- 适用于水质监测、海洋生态研究者及环境管理者
硝酸盐（NO₃⁻）主要来自人为源，其河流输入量上升对大堡礁潟湖的珊瑚白化构成重大威胁。尽管硝酸盐本身无色（光学惰性），但其与水体反射率存在间接非因果关系，受悬浮物和有色溶解有机物等光学活性参数介导。本研究在昆士兰菲茨罗伊河河口开展时序观测，利用深度学习模型，基于高光谱反射率与盐度数据预测水面硝酸盐浓度。结果表明，潮汐影响导致硝酸盐负荷呈周期性变化；模型预测值与实测值相关性良好，R²达0.86，均方根误差为0.03 mg/L。该研究证明了通过高光谱反射率与盐度联合预测硝酸盐的可行性。
原文摘要 · Abstract (English)
Nitrate ($\text{NO}_3^-$) is a form of dissolved inorganic nitrogen derived primarily from anthropogenic sources. The recent increase in river-discharged nitrate poses a major risk for coral bleaching in the Great Barrier Reef (GBR) lagoon. Although nitrate is an optically inactive (i.e., colourless) constituent, previous studies have demonstrated there is an indirect, non-causal relationship between water surface nitrate and water-leaving reflectance that is mediated through optically active water quality parameters such as total suspended solids and coloured dissolved organic matter. This work aims to advance our understanding of this relationship with an effort to measure time-series nitrate and simultaneous hyperspectral reflectance at the Fitzroy River estuary, Queensland, Australia. Time-series observations revealed periodic cycles in nitrate loads due to the tidal influence in the estuarine study site. The water surface nitrate loads were predicted from hyperspectral reflectance and water salinity measurements, with hyperspectral reflectance indicating the concentrations of optically active variables and salinity indicating the mixing of river water and seawater proportions. The accuracy assessment of model-predicted nitrate against in-situ measured nitrate values showed that the predicted nitrate values correlated well with the ground-truth data, with an $R^2$ score of 0.86, and an RMSE of 0.03 mg/L. This work demonstrates the feasibility of predicting water surface nitrate from hyperspectral reflectance and salinity measurements.
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