Bistatic Radar: A New Path To The Detection And Monitoring Of Phytoplankton Blooms

Phytoplankton plays a key role in the global carbon cycle and the ocean biogeochemistry. When an excess of nutrients is supplied into the ocean, combined with sunlight, it can trigger phytoplankton blooms. Those blooms impact ecosystems and can alter or kill the seafloor plants and fish population in the affected areas. The presence of phytoplankton blooms has also important impacts on the economy as fishermen activities, seafood industry, coastal property owners, tourism operators and health officials are affected. Gaining information on those blooms is key to those agents. Phytoplankton blooms form a film on the ocean surface changing the ocean surface tension. This change in ocean surface tension causes a local decrease of ocean surface roughness over the areas affected. Bistatic radar data from the CYclone Global Navigation Satellite System (CYGNSS) mission can detect changes in the ocean surface roughness, expressed as an increase in reflectivity when the ocean surface becomes smoother. We will present our investigations of four cases: (1) the massive dust storm formed over the Sahara Desert in June 2020, (2) the recurrent phytoplankton blooms in the Arabian sea, (3) the massive blooms that occur at Qingdao on the East coast of China, and (4) the red tide that occurred in 2018 in the coast of Florida. We recently published the research on the Saharan dust storm event and found strong signatures in the bistatic radar data showing abnormally low ocean surface roughness in the Gulf of Mexico. CYGNSS data offers unprecedented spatial and temporal coverage that allows for the analysis of those signatures at time scales of 1-day, robust to the presence of clouds and dust clouds. The capability of bistatic radar for detecting and monitoring phytoplankton blooms is a new application to the bistatic radar field, adding value to characterize a very dynamic phenomena that is difficult to predict and that requires timely measurements to enable global monitoring systems.