Multi-satellite Observation of a Harmful Algal Bloom in the Beibu Gulf, South China Sea

In mid-February of 2021, a harmful algal bloom (HAB) dominated by the Noctiluca scintillans occurred and lasted several days in the Beibu Gulf, South China Sea. Here in this work, we investigated the HAB event using optical and thermal infrared remote sensing data from multi satellites. The bloom spatial information of location and areal extent were determined based on bloom image features from the optical measurements of HY-1C/D and MODIS Aqua. The thermal infrared images from MODIS Aqua, NPP VIIRS and Himawari-8 were used to obtain the sea surface temperature (SST) characteristics in the study area during the bloom period. Then, short-term temperature changes of the bloom and normal sea areas were further analyzed. The SST images showed a warming anomaly between the bloom and surrounding normal sea areas on February 14. The warming anomaly appeared at 10 : 00 and then changed through the course of a day, finally it disappeared after 21 : 00, with a maximum temperature difference (Delta T) of 2.5 degrees C around 15 : 00. Considering the close time-space correlation between SST and bloom, the bloom outbreak may have caused the SST anomalies. This study demonstrates the unique value of multi-satellite remote sensing data in revealing short-term changes related to HABs.