The Fluorescence Line Height (FLH) data suite quantifies the red chlorophyll-a fluorescence (~678–683 nm) emitted by phytoplankton, computed as the height of the measured water-leaving radiance above a spectrally interpolated baseline. FLH is widely used for HAB detection and tracking, identifying productive waters, and assessing phytoplankton physiology; values tend to be elevated in active blooms and can be reduced in complex waters. As with all ocean-color products, uncertainties increase in optically complex coastal/inland waters, so users should refer to mission/algorithm notes for details.

Geophysical variables in this suite include:
• nflh — Normalized Fluorescence Line Height (W m⁻² µm⁻¹ sr⁻¹)