Review of the Forel–Ule Index based on in situ and remote sensing methods and application in water quality assessment

• Published in: Environmental science and pollution research international Vol. 29; no. 9; pp. 13024 - 13041
• Main Authors: Ye, Miao, Sun, Yonghua
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2022; Springer Nature B.V
• Subjects: absorption; Algorithms; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; color; Color measurement; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Environmental Monitoring; Environmental science; Inland waters; Natural waters; Oceans; Oceans and Seas; Optical activity; Parameters; Quality assessment; Quality control; reflectance; Remote sensing; Remote Sensing Technology; Retrieval; Review Article; Waste Water Technology; Water Management; Water pollution; Water Pollution - analysis; Water Pollution Control; Water Quality; Water quality assessments; Hue angle; Forel–Ule scale; Forel–Ule Index; Remote sensing; Water quality; Water colour
• ISSN: 0944-1344; 1614-7499; 1614-7499
• DOI: 10.1007/s11356-021-18083-0

Water pollution is considered an acute worldwide environmental issue. At present, the commonly adopted method of water quality characterisation involves the retrieval of optically active water quality parameters based on remote sensing reflectance (R rs ), but this method is subject to the limitation that understanding local scatter and absorption characteristics of light is essential to precisely derive these parameters. Water colour primarily depends on water constituents and is traditionally gauged with the Forel–Ule (FU) scale. In recent years, R rs within the visible region has been considered to determine the Forel–Ule Index (FUI) for water colour measurement. The FUI exhibits the advantages of remote sensing and does not rely on local retrieval algorithms. Therefore, this index can characterise natural waters in a simple and globally effective manner. As there exists a lack of review articles on the FUI, we present a comprehensive review of this index that may help researchers progress. First, we introduce the most recent techniques for FUI measurement, especially remote sensing–deriving methods. Then, we summarise FUI applications in water quality assessment of oceans and inland waters. Finally, FUI development trends, challenges and application perspectives are examined.