October 29, 2018

Forecasting weather and understanding climate with CFOSat

CFOSat (China-France Oceanography Satellite) was launched today, Monday 29 October, into low Earth orbit. This first joint mission with China is set to deliver data for weather forecasting and long-term climate research. Thierry Amiot, principal investigator for the satellite’s SWIM instrument at CNES, and Lotfi Aouf, a research scientist at the French national weather service Meteo-France, explain.

CFOSat is a first in more ways than one. When the Chinese CZ-2C launcher lifted off today from the Jiuquan base in the middle of the desert, it was carrying the French-Chinese satellite developed jointly by CNES and the China National Space Administration (CNSA). Perched in Sun-synchronous low Earth orbit at an altitude of 520 km, this 650-kg satellite is carrying two instruments: the French SWIM (Surface Waves Investigation and Monitoring) and the Chinese SCAT (wind SCATterometer). SCAT is a radar capable of measuring the properties of sea winds, while SWIM will characterize ocean waves.

But it’s by combining the capabilities of both instruments that CFOSat comes into its own. “SWIM is what we call a wave scatterometer. It’s the first Ku-band radar in space operating with six rotating beams to characterize ocean waves, so it’s highly innovative,” says Thierry Amiot.
“It’s the first time we’ll be able to obtain simultaneous and co-located measurements of winds and of the directional spectrum of waves, in other words their length, height and direction. at Meteo-France, we’re expecting to learn a great deal from these data,” confirms Lotfi Aouf.

Replay of CFOSat launch

From detection to forecasting

CNES’s contribution to CFOSat isn’t limited to the SWIM instrument developed and built by Thales Alenia Space, since France also supplied part of the X-band subsystem that will send SWIM and SCAT data back to ground stations and to the mission centre. “SCAT and SWIM data acquired on the satellite are copied and sent as such to a network of Chinese ground stations and to the French network that consists of receiving antennas in Inuvik, Canada, and Kiruna, Sweden. These stations then relay the raw data for processing to the mission centre at CNES in Toulouse and then to Ifremer, the French institute of marine research and exploration in Brest,” explains Thierry Amiot. “Every effort is made to get the data to users less than three hours after acquisition.”

This is because the wind and wave data might be needed to issue weather warnings. “The data are sent directly to our operations centre and will be fed in near-real time into our sea-state and weather prediction models. This will enable Meteo-France to issue reliable coastal flood warnings and assure the safety of people and assets onshore and out at sea. With CFOSat, we’ll get a snapshot of the current weather picture as well as long-term, global data to feed and constrain our models,” adds Lotfi Aouf.

From forecasting to global models

For while satellites currently in orbit provide some data on ocean waves from altimeters and imaging radars, they aren’t able like CFOSat to fully characterize them in all directions and correlate them with winds. These are precisely the key parameters required to better force models predicting ocean conditions (notably when tracking severe sea-state events), which are used not only for weather forecasting but also by scientists studying climate change.

Such information can be obtained locally from data buoys or ships, or from aerial surveys like that performed for the precursor of SWIM, the KuROS airborne radar developed by the LATMOS atmospheres, environments and space observations laboratory with support from CNES. A satellite like CFOSat can deliver such measurements for all of Earth’s oceans.

Teams are already seeing good results from this joint mission with China. “The Chinese are keen to advance their ability to assimilate large volumes of data for their weather prediction models, so this partnership is a big challenge for them as they get to grips with our methods” says Lotfi Aouf, who adds that an exchange of researchers is soon set to be organized between Meteo-France and the National Marine Environmental Forecasting Center (NMEFC) in Beijing. Technical exchanges have been ongoing for several years now.

“Over the last 10 years, we’ve been working together a lot and conducted numerous tests with our Chinese partners to put SWIM on CFOSat. Last year was devoted to assembly, integration and testing of the satellite in China (at the start of August 2017). Moreover, while SWIM and SCAT are operating independently on the satellite, their transmission frequencies are very close to one another, so we had to adapt the instruments to avoid interference. Dedicated tests were even performed in China to check their compatibility. Lastly, we also had to exchange ground processing tools so that both nations can exploit the two types of data delivered by SWIM and SCAT,” concludes Thierry Amiot.


Thierry Amiot
SWIM instrument principal investigator

E-mail: thierry.amiot at cnes.fr

Tel.: +33 (0)5 61 27 39 17

Artist’s impression of the CFOSat satellite in action. Credits CNES/CNSA

The CFOSat satellite just before final integration of its solar panels and mating with the launcher interface (autumn 2018). Credits CNES/CNSA