Fig. 1. The relationship between the main components of Natural Organic Matter （NOM） in inland waters

Fig. 2. Characteristics of DOC content in different waters around the world

Fig. 3. Concentration range of CDOM at specific wavelengths in different types of waters around the world^{［34，42-55］}

Fig. 4. Distance density diagram of Chinese and English keywords

Fig. 5. Overview of the retrieval model of CDOM （440）