First Light Demonstration of Red Solar Induced Fluorescence for Harmful Algal Bloom Monitoring

The risks harmful algal blooms (HAB) pose to aquatic ecosystems, public health, and coastal economies necessitate supplementation of current observation strategies. Herein, we explore the use of red solar induced fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI), a remote sensing measurement retrievable in variable cloud conditions, for Karenia brevis detection. Along the West Florida Shelf from 2018-2020, we compare red SIF with normalized fluorescence line height (nFLH) from MODIS-Aqua, a standard remote sensing HAB indicator limited to clear sky days. A strong linear relationship is found between nFLH and red SIF during severe bloom conditions in 2018 (N = 29,562, r-value = 0.8, R2=0.64) permitting direct comparison. Red SIF provided nearly double the amount of spatiotemporal fluorescence information than nFLH. This work presents the first application of TROPOMI's red SIF for HAB monitoring and illuminates an approach for bolstering early warning systems for HABs beyond clear sky conditions.

有害藻华（Harmful Algal Blooms, HAB）对水生生态系统、公共卫生及沿海经济构成的风险，使得现有观测策略亟需补充完善。本研究探讨利用对流层监测仪器（TROPOspheric Monitoring Instrument, TROPOMI）获取的红色日光诱导荧光（Solar Induced Fluorescence, SIF）开展短凯伦藻（Karenia brevis）探测的可行性，该遥感观测可在多变云况下反演获取。在2018至2020年的西佛罗里达陆架海域，我们将红色SIF与Aqua卫星中分辨率成像光谱仪（MODIS-Aqua）的归一化荧光线高度（normalized fluorescence line height, nFLH）进行对比——后者作为HAB遥感监测的标准指示因子，仅适用于晴朗天空时段。2018年重度藻华暴发期间，nFLH与红色SIF间呈现显著线性相关关系（样本量N=29562，相关系数r=0.8，决定系数R²=0.64），为二者的直接对比提供了依据。红色SIF所提供的时空荧光信息量近乎为nFLH的两倍。本研究首次将TROPOMI的红色SIF应用于HAB监测，为突破晴朗天空条件限制、强化藻华早期预警体系提供了可行技术路径。