Water quality indication of spectral probability distribution (SPD): correlation between SPD and Forel-Ule index in closed, connected water bodies

The spectral probability distributions (SPD) of water bodies in satellite images have demonstrated the potential for indicating the geographical and environmental features of their watersheds. This implies that SPDs also have the potential for indicating water quality features, but so far there have been no further studies on their correlations. In this study, 690 SPDs of global closed connected water bodies, mainly including lakes and reservoirs, were extracted from Landsat-8 images. These SPDs were classified into seven types, and the entropy of each SPD diagram was calculated. The correlation between the SPD diagram's entropy and Forel-Ule index (FUI) is relatively good with R-2 = 0.5651 - indicating that water bodies with better water quality are usually found to have smaller entropy in their SPD diagrams. This study demonstrates that SPD is a good indicator for not only the aquatic environment but also water quality monitoring.