The Aeolus satellite returned to Earth on 28 July 2023, in an assisted reentry that marked the end of nearly five years in space. For scientists working with Aeolus data, however, the mission lives on. Over the next five years, data reprocessing and analysis will continue to improve weather and climate models, paving the way for future space lidars.

“You could say this is just the beginning,” said Tommaso Parrinello, Aeolus Mission Manager, in the aftermath of ESA’s wind satellite’s trailblazing descent back to Earth.

Aeolus pioneered a safe return to Earth for satellites not designed for controlled reentry, but before that it became the first ever satellite to acquire vertical profiles of Earth’s wind on a global scale.

For weather forecasters and atmospheric dynamics researchers, Aeolus provided a veritable bonanza of novel information, particularly in hard-to-measure areas of the globe such as the tropics. The satellite’s wind data significantly improved global weather forecasts.

Aeolus is now entering Phase F of its mission, which follows the operational Phase E2. The objective of Phase F is to provide high quality, validated wind and aerosol/cloud products that continue the mission’s positive impacts on numerical weather prediction and enable new atmospheric dynamics studies.

Phase F will run for five years, ending on the last day of 2028. During that time the Aeolus data, innovation, and science cluster (DISC) will continue to fine-tune Aeolus data to bolster weather and climate models.

So, what happens next for Aeolus data, and what can users expect?

Data reprocessing timeline

Data reprocessing by the DISC has been key to improving the quality of Aeolus measurements. It involves the assimilation of new and improved algorithms to correct biases and reduce errors.

For users, data upgrades can always be found on the ALADIN Processor Releases webpage.

A high-level timeline for Phase F is as follows:

• Spring 2024: Baseline 16 reprocessed FM-B data will become publicly available, including an improved Rayleigh cloudy product and improvements of baseline 15 and 16 data. Following tests, we expect better Level-1b, Level-2a and Level-2b data quality, mainly due to improved Hot Pixel correction.
• Spring 2025: Baseline 16 reprocessed FM-A data will become available, marking the first time we have a uniformly processed Aeolus dataset covering the entire mission.
• 2026-2027: Baseline 17 reprocessed data will become available, including a novel land surface reflectance product based on an Aeolus+ project headed by KNMI, as well as improvements to the scattering ratio and signal-to-noise ratio. This will improve all Level-2a aerosol and cloud products and the discrimination of Level-2b clear and cloudy winds. The estimated error calculations for Mie and Rayleigh winds will become more accurate.
• 2028: Baseline 18 will be the final reprocessed dataset. This will likely not include any data quality changes, but improvements to data description and usability, as well as the suitability to long-time data archiving. 

Analysing Aeolus’s lifetime in space

Whilst data reprocessing continues in earnest, the lessons learned from Aeolus will continue its legacy.

Aeolus’ successful reentry, a first of its kind, provides a template for future missions that were never designed for a controlled return to Earth.

The first workshop dedicated to lessons learned from the reentry will take place at the end of November 2023.

End-of-life tests, conducted in the weeks before Aeolus reentered, helped scientists and engineers eke the most out of a mission that may have continued if it weren’t for lack of fuel and increased solar activity dragging it home.

They included ramping up the ALADIN laser to record energy levels for a spaceborne UV laser, as well as detailed investigation of in-orbit issues.

The first analysis of Aeolus’ end-of-life tests will be presented at the upcoming Aeolus Scientific Advisory Group meeting in early November 2023.

Such reflections will help to inform the development of the operational follow-on mission Aeolus-2/EPS-Aeolus, which is set to launch within a decade after receiving full support at ESA’s ministerial in 2022.

Preparatory work is ongoing ahead of a decision in 2025, whether to proceed with the follow-on mission. Aeolus-2 would see ten years’ worth of operational wind observations that could reap significant economic benefits to Europe worth around €7.1 billion.