Normalized Dynamic Fluorescence Height: An Alternative Algorithm for Chlorophyll a Estimation in Algae-Dominated Waters Using Hyperspectral Remote Sensing Reflectance from In Situ and Spaceborne Imagers

The accurate determination of chlorophyll a (Chl a) is often limited by the instability of conventional fluorescence height algorithms in algal bloom waters characterized by diverse phytoplankton morphology and red-shifted reflectance peaks. In this study, we propose the Normalized Dynamic Fluorescence Height (NDFH) as a novel hyperspectral algorithm for assessing sun-induced chlorophyll fluorescence. Using in situ bio-optical data and multi-source satellite observations (Advanced Hyperspectral Imager (AHSI) onboard ZY-1E, Hyperspectral Imager for the Coastal Ocean (HICO) onboard ISS, and Ocean Color Instrument (OCI) onboard PACE), NDFH was evaluated and compared with existing algorithms, such as the normalized Fluorescence Line Height, Cyanobacterial Index (CI), and Maximum Algal Line Height (MALH). The results show that NDFH has robust exponential correlations with Chl a concentrations in inland waters and can reliably detect fluorescence peak band shifts in bloom-dominated environments. Case studies in Lake Taihu confirm that NDFH is more effective at delineating bloom extent and Chl a distributions than conventional methods, particularly in algae-dominated waters. These findings show the potential of NDFH for operational monitoring of eutrophication and harmful algal blooms across diverse aquatic environments.