Observation of Harmful Algal Blooms with Ocean Colour Radiometry

Harmful algal blooms (HABs) and eutrophication events have had a significant global impact over the past few years. The frequency of these events, and the geographic extent of toxic/harmful algal blooms have been increasing globally. For this reason a joint working group was formed between the IOCCG and the GEOHAB Programme (now GlobalHAB) of SCOR and the Intergovernmental Oceanographic Commission (IOC) of UNESCO, tasked with producing a comprehensive guide to satellite ocean colour remote sensing of HABs. The report summarises the state of knowledge and demonstrates the suitability of various ocean colour approaches through case studies from different ecosystems, as well as operational HAB applications. The primary focus areas are the technical difficulties of using ocean colour remote sensing in optically-complex coastal waters, and the need to understand the limitations of ocean colour for deriving phytoplankton community composition. A major conclusion was that ocean colour remote sensing is effective in detecting high biomass blooms, but does not work well for low biomass blooms, which can be addressed using indirect approaches.