Trophic state assessment of global inland waters using a MODIS-derived Forel-Ule index

• Published in: Remote sensing of environment Vol. 217; pp. 444 - 460
• Main Authors: Wang, Shenglei, Li, Junsheng, Zhang, Bing, Spyrakos, Evangelos, Tyler, Andrew N., Shen, Qian, Zhang, Fangfang, Kuster, Tiit, Lehmann, Moritz K., Wu, Yanhong, Peng, Dailiang
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01.11.2018; Elsevier BV
• Subjects: Algorithms; Central Africa; Central Asia; Chlorophyll; color; data collection; Dissolved organic matter; East Asia; Eutrophic lakes; Eutrophication; Forel-Ule index; Global inland waters; Imagery; In situ measurement; Inland waters; Lakes; moderate resolution imaging spectroradiometer; MODIS; North America; Optical activity; Optical properties; Reflectance; Remote sensing; Retrieval; satellites; South America; Spectroradiometers; summer; surface area; Surface water; Trophic state; Water quality; Asia; South America; East Asia; Central Africa; Central Asia; North America; Global inland waters; Trophic state; Forel-Ule index; MODIS
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2018.08.026

Eutrophication of inland waters is considered a serious global environmental problem. Satellite remote sensing (RS) has been established as an important source of information to determine the trophic state of inland waters through the retrieval of optically active water quality parameters such as chlorophyll-a (Chl-a). However, the use of RS techniques for assessment of the trophic state of inland waters on a global scale is hindered by the performance of retrieval algorithms over highly dynamic and complex optical properties that characterize many of these systems. In this study, we developed a new RS approach to assess the trophic state of global inland water bodies based on Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and the Forel-Ule index (FUI). First, the FUI was calculated from MODIS data by dividing natural water colour into 21 indices from dark blue to yellowish-brown. Then the relationship between FUI and the trophic state index (TSI) was established based on in-situ measurements and MODIS products. The water-leaving reflectance at 645 nm band was employed to distinguish coloured dissolved organic matter (CDOM)-dominated systems in the FUI-based trophic state assessment. Based on the analysis, the FUI-based trophic state assessment method was developed and applied to assess the trophic states of 2058 large inland water bodies (surface area >25 km2) distributed around the world using MODIS data from the austral and boreal summers of 2012. Our results showed that FUI can be retrieved from MODIS with a considerable accuracy (92.5%, R2 = 0.92) by comparing with concurrent in situ measurements over a wide range of lakes, and the overall accuracy of the FUI-based trophic state assessment method is 80.0% (R2 = 0.75) validated by an independent dataset. Of the global large water bodies considered, oligotrophic large lakes were found to be concentrated in plateau regions in central Asia and southern South America, while eutrophic large lakes were concentrated in central Africa, eastern Asia, and mid-northern and southeast North America. •Present a trophic state assessment method for global large inland waters based on MODIS.•Produce the trophic state map of global large inland water bodies.•Analyze the spatial distribution of the trophic states of global large inland water bodies.