ESA’s Soil Moisture and Ocean Salinity (SMOS) satellite has been in orbit for almost 10 years. As its name describes, SMOS collects soil moisture and ocean salinity data to increase knowledge about the water cycle, as well as to measure the wind speed of extreme weather.
During a storm, thick swirling clouds and strong winds create a volatile environment, pushing up waves and whitecaps (the sea-foam crest over the waves). Satellites typically use microwave scatterometers to gather information on the storm’s wind speed from the whipped up waves/whitecaps. But when intensity increases, a tropical storm’s strong winds can flatten the waves.
However, wind speed can be gathered by another metric. Wind-generated foam affects the surface’s microwave emissions. Scientists can thus link radiation change with wind strength over the sea.
Thankfully, SMOS has a microwave radiometer onboard that can detect the surface’s microwave emissions and measure hurricane-force wind speeds from space. According to the ESA, the microwave radiometer captures “images of brightness temperature. Measurements correspond to radiation emitted from Earth’s surface, which are then used to derive information on soil moisture and ocean salinity.”
“While advances in our understanding of the physics underpinning the life cycle of tropical storms and their development into hurricanes and cyclones are advancing all the time, there is no substitute for improved measurement capability that can help define the character of a given storm,” says Nicolas Reul, from Ifremer. “Although SMOS data have a spatial resolution of 40 km, the wide-swath regular repeat coverage and ability to provide measurements of surface-wind speed structure at hurricane force in the presence of heavy precipitation is unique.”
Experiments show that SMOS contributions can “help improve errors in forecast lead times by 36–72 hours in the extratropics,” the ESA reports.
A pre-operational SMOS wind-data service has been established by the ESA, OceanDataLab, and Ifreme. It provides ocean-surface wind speeds in near-real time (three to six hours from sensing) to a select few users, including the U.S. Naval Research Laboratory, Joint Typhoon Warning Centre, and NOAA National Hurricane Center. Its potential benefits are currently being assessed.
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