Delivering new information about Earth’s winds, ESA’s Aeolus mission has already been hailed a success. Today, this remarkable satellite mission has yet again achieved new heights: its data are now being distributed publicly to forecasting services and scientific users in less than three hours of measurements being made from space.
Aeolus is one of ESA’s Earth Explorer missions, which all set out to demonstrate how new ways of observing Earth can advance our understanding of how the planet works as a system.
Carrying one of the most sophisticated instruments ever to be put into orbit, Aeolus is the first satellite mission to directly profile Earth’s winds from space.
It works by emitting short, powerful pulses of ultraviolet light from a laser and measures the Doppler shift from the very small amount of light that is scattered back to the instrument from molecules and particles to deliver vertical profiles that show the horizontal speed of the world’s winds in the lowermost 26 km of the atmosphere.
ESA’s Director of Earth Observation Programmes, Josef Aschbacher, said, “Aeolus was never going to be an easy satellite mission to develop, and, indeed, it took some years to get it right before it could be launched. The wait was certainly worth it though, and in the 20 months that it has been in orbit, it has gone from strength to strength that will lead to benefits for science and society alike.
“And, thanks to all the teams involved and in agreement with EUMETSAT, we are very proud to announce that as of today, Aeolus’ data are being distributed in near-real time for numerical weather prediction beyond the Aeolus core user community.”
ESA’s Peggy Fischer said, “A huge amount of work has gone into perfecting Aeolus’ data before today’s public release. This satellite technology is completely new so we have had to understand and correct certain biases in the data that were not known before launch.
“To do this, key Aeolus experts from different organisations worked together in the Data Innovation and Science Cluster team – the Aeolus DISC, to validate and optimise the data processing and bias correction methods.”
ESA’s Jonas von Bismarck, added “As the last and particularly tricky bit of the puzzle, a bias related to temperature variations across the instrument’s telescope was corrected, making the data ready to be used in numerical weather prediction without the forecast centres having to carry out further complex corrections.”
The European Centre for Medium-Range Weather Forecasts (ECMWF) in the UK has already been including Aeolus data in their forecasts since January, relying on their own bias correction scheme.
Florence Rabier, Director-General at ECMWF, said, “After several months of testing last year we were confident of assimilating Aeolus wind data into our forecasts, which we’ve been doing since this January. We are now thrilled to see that the last biases have been corrected, benefiting us and additional weather centres that are getting ready to use the data.”
These new data are being distributed in near real-time through ESA’s Aeolus Online Dissemination Centreas well as other channels, namely EUMETCast, which is the European Organisation for the Exploitation of Meteorological Satellites’ (EUMETSAT’s) dissemination system, and the World Meteorological Organization’s Global Telecommunication System (GTS).
With Aeolus built as a research and demonstrator mission, it has shown its worth as an operational mission with the data being used for everyday weather forecasting, paving the way for a possible future fleet of operational Doppler wind lidar satellites in space.
Alain Ratier, Director-General of EUMETSAT, concluded, “EUMETSAT will now push Aeolus data in near-real time to the 4000 users of EUMETCast and to the full WMO community, to give the opportunity to every forecast centre to familiarise with the novel data and measure their value. This user feedback, together with the results of on-going ESA instrument and satellite studies, will support our planning of a possible operational Doppler Lidar mission adding a missing wind profiling capability to our next generation EPS-SG polar system.”
Joining forces for Aeolus
For a team of scientists and technicians from Europe and the US, the fact of ‘going back to the office’ this September has meant heading off to the Cabo Verde islands in the Atlantic – not to extend their summer holidays, but for a complex international experiment campaign that will scrutinise the data being delivered by one of today’s most innovative Earth observation satellites: ESA’s Aeolus wind mission.
Since it was launched three years ago, Aeolus has far exceeded expectations and frequently hailed a remarkable success. It was developed as a research mission and to demonstrate how novel laser technology could deliver vertical profiles of Earth’s wind. These measurements were much needed, for example by the World Meteorological Organization’s Global Observing System, which is a coordinated system of methods and facilities for making meteorological and environmental observations on a global scale.
Despite Aeolus being built as a research and demonstrator mission, it has proven to be so good that, for more than a year now, its data have been distributed publicly to forecasting services and scientific users in less than three hours of measurements being made from space.
Playing such an important part in forecasting, and with a potential follow-on satellite mission on the table, it is critical to ensure that its data are accurate, particularly for forecasts in the Tropics where large weather systems develop and where Aeolus is said to be making a real difference.
Hence, scientists from ESA, NASA, the German Aerospace Center, the French National Centre for Scientific Research, the CNES French space agency, Météo-France, Atmospheres Spatial Observations Laboratory, the National Observatory of Athens, the Leibniz Institute for Tropospheric Research, the University of Nova Gorica, the Ocean Science Centre Mindelo, and from many other institutes are all joining forces in Cabo Verde and also in the Virgin Islands for the Aeolus tropical Atlantic campaign.
The Cabo Verde islands lie about 600 km off the coast west Africa. This tropical location is not only relevant for Aeolus, but it is also where strong winds often carry desert dust and aerosols from the African continent across the islands, making it an ideal place for investigating cloud–aerosol interaction and atmospheric dynamics.
Throughout the month, this intrepid team are taking measurements of the wind, aerosols and clouds with a range of instrumentation on different aircraft flying at different altitudes.
Many flights are even coinciding with Aeolus as it orbits above. Measurements are also being taken by lasers and radars on the ground. This is all providing a wealth of data to compare with that from Aeolus and to support the science to tropical weather.
Thorsten Fehr, head of the atmospheric section at ESA, said, “We had hoped to run the field campaign last year, but of course the Covid pandemic thwarted our plans. It is an extremely complicated campaign and has been a mammoth task for us and our teams to arrange.
“This is truly an international effort and we are all thrilled to have the campaign now well underway, especially given Covid. I can’t thank everyone enough for all the work they’ve done to make it a reality.
“This extraordinary experiment campaign brings huge benefits, not only to our Aeolus mission, but also to our upcoming EarthCARE mission that is set to advance our understanding of the role that clouds and aerosols play in reflecting incident solar radiation back out to space and how the trap infrared radiation emitted from Earth’s surface.
“In addition, the data we collect will help in development of an Earth Explorer mission concept called Wivern, which aims to measure wind in clouds.
“You could never achieve an experiment of this scale without working together. International collaboration is key to so much of what we do, and we naturally build strong bonds our colleagues. So, we were deeply saddened by the sudden loss of a dear NASA colleague last week, which understandably led to NASA having to suspend their operations. Our thoughts and sincere condolences go to Gail Skofronick-Jackson’s family, friends and colleagues.”
ESA’s Aeolus mission manager, Tommaso Parrinello, said, “We are all extremely shocked by the tragic loss of Gail. NASA had been supporting our campaign in the Virgin Islands well before the fleet of European aircraft arrived in Cabo Verde and they had planned to join the team here for their second part of the campaign.
“We now hope that we will be able to resume this part of the campaign next year.”
Aeolus’ fiery demise to set standard for safe reentry
ESA’s wind mission, Aeolus, will soon be lowered in orbit leading to its fiery reentry and burn-up through Earth’s atmosphere. ESA’s efforts to ensure a safe return go well beyond international standards and place the Agency in the lead for space safety.
Having exceeded its planned life in orbit, the 1360-kg satellite is running out of fuel. Ensuring that enough fuel remains for a few final manoeuvres, ESA’s spacecraft operators will bring Aeolus back towards our planet’s atmosphere for its inevitable demise.
They will aim the mission towards the ocean, further reducing the very small chance that fragments could cause harm should any reach Earth’s surface.
This is the first assisted reentry of its kind and sets a precedent for a responsible approach to reduce the ever-increasing problem of space debris and uncontrolled reentries.
Why is Aeolus coming home?
Launched in 2018, Aeolus has outlived its planned three-year life in space by more than 18 months. During its mission, its trailblazing wind-mapping laser, which at one stage was thought a nigh-impossible feat of engineering, has significantly improved weather forecasts worldwide.
Aeolus has been hailed as one of the most successful missions ever built and flown by ESA. As an Earth Explorer research mission, it was designed to demonstrate new space technology, but it became one of the highest impact-per-observation weather satellites, and its laser is still performing as well as ever.
However, Aeolus’ fuel is now almost depleted and orbiting low, at an altitude of just 320 km, means it is already being caught up by Earth’s wispy atmosphere.
Speeding up Aeolus’ return is the Sun.
Solar flares and coronal mass ejections release matter and radiation, and when this washes past Earth, it increases the density of Earth’s atmosphere. Intense solar activity in recent months means that the satellite has been using even more fuel to remain in orbit. For Aeolus, it’s been like running against the wind.
This is why, after five years of spectacular science, ESA’s wind mission ended operations on 30 April 2023.
Making use of this phase, scientists have put its instrument into a special mode to perform end-of-life activities that will help to prepare the Aeolus-2 follow-on mission, which like a phoenix will emerge from the ashes of its pathfinding predecessor.
Aeolus’ final breaths
Over the next few months, Aeolus will descend naturally from its current altitude of 320 km to 280 km. At this point, spacecraft operators at ESA’s mission control centre, ESOC, in Darmstadt, Germany, will gradually lower it to 150 km above Earth’s surface. The satellite will burn up as it descends to around 80 km.
As populated regions make up a relatively small percentage of Earth’s surface, the chance of a re-entry causing any harm is exceptionally low.
The final date depends on how solar activity speeds up the process, but Aeolus is expected to be no more before the end of August.
Aeolus engineers and industry partners have carefully worked out how to best position Aeolus in Earth’s atmosphere to target open ocean waters upon reentry, hugely reducing the amount of land over which pieces fragments could fall.
ESA’s Aeolus Mission Manager, Tommaso Parrinello, said, “The exact details on the reentry approach and series of manoeuvres and operations, as well as a more detailed timeline will be made public in mid-June.
“For now, we can anticipate that we are targeting the best ocean corridor to reenter.”
With the assisted reentry of Aeolus, ESA is clearing the way for future missions to continue taking the pulse of our planet. They can only do this if Earth’s orbits aren’t filled with dangerous space debris, and safety is at the forefront of end-of-life activities.