ESA's Aeolus satellite has returned to the Earth's atmosphere from an altitude of 320 kilometers after a very successful mission. Satellites usually descend slowly due to the Earth's gravity, but ESA has achieved the first controlled reentry of a satellite into the atmosphere. The following is a brief review of scientific experiments involving the Leibniz Tropospheric Institute (TROPOS) that were conducted shortly before the end of the Aeolus mission:
The final image of Aeolus as a transitory phase of space debris acquired by Fraunhofer FHR's space observation radar TIRA. (Note that the color represents the radar echo intensity, not the temperature).
Aeolus is the first space mission to obtain global wind profiles. Image source: ESA/ATGmedialab
The Aeolus satellite was launched on August 22, 2018 and has been in Earth orbit for nearly five years while providing vertical profiles of horizontal wind speeds and backscatter information from clouds and aerosols. From the beginning to the end of the mission, TROPOS provided continuous reference measurement data from around the world for validating wind and aerosol/cloud products, contributing significantly to the mission's resounding success. After the mission, TROPOS will also participate in the Aeolus Data, Innovation and Science Cluster (DISC) project to improve data products and increase the scientific impact of the mission. TROPOS is involved in the development of Class 2A aerosol optical characterization products, monitors data quality and supports external validation together with scientific teams from European partners.
Analysis of Aeolus vertical wind test results. Left: Cloud top height (via the GOES-R geostationary satellite) and the measured trajectory of Aeolus. Right: Aeolus signal level when measured nadir above clouds. The yellow line shows the cloud top height from GOES-R. Source: Sebastian Bley, TROPOS
Before the satellite was scrapped in history, the Aeolus team successfully conducted a series of scrapping experiments. Scientists hope these experimental results will help improve future space lidar missions. Each test was conducted in collaboration with AeolusDISC to evaluate the instrument's radiation performance and impact on aerosol and wind products.
TROPOS participated in an experiment that tilted the laser from its nominal 35-degree diagonal view to a nadir view (the point on the Earth's surface directly below the satellite) to measure vertical winds over deep convective cloud systems. Although vertical air motion is negligible on average over large horizontal scales, in severe convective situations (such as tropical storms) this assumption does not hold. Dr Sebastian Bley of TROPOS said: "While we are still analyzing the promising data collected during this test, we hope to be able to quantify the impact of vertical air movement on the assumptions used."
TROPOS is also involved in ATLID testing, configuring the Aeolus laser ALADIN to mimic the ATLID lidar that will fly on EarthCARE. The purpose of this test is to prepare for the upcoming launch of the EarthCARE satellite, which will carry an instrument very similar to the lidar on Aeolus. "The lessons learned from Aeolus have greatly helped us prepare for the EarthCARE mission. Carrying four instruments measuring aerosols, clouds and radiation on one platform is more challenging than Aeolus," said Dr. Ulla Wandinger of TROPOS. The launch window for the EarthCARE mission is currently scheduled for April to June 2024. During the ATLID test, Aeolus flew over Leipzig and Mindelo in the Cape Verde Islands, both sites with ground-based lidar instruments operated by TROPOS.
TROPOS' final statement
We are following the re-entry event of "Aeolus" with mixed emotions. On the one hand, we are sad that this wonderful satellite burned up in the Earth's atmosphere; on the other hand, we are happy and proud to have contributed to the success of this exciting mission.
But there are also reasons to look to a bright future. Our work will continue long after Aeolus lights up the sky like a meteor for the last time. Our colleagues at TROPOS will continue to study the past five years of Aeolus data in the AeolusDISC project, particularly to validate the reprocessed aerosol products and highlight new applications for the atmospheric science community.
In addition, we are actively involved in the preparations for the EarthCARE mission, which will be launched next summer. Within the framework of the ESA-CARDINAL project, TROPOS has played a leading role in the development of the ATLID lidar processor and multispectral imager (MSI) cloud products. Additionally, TROPOS is preparing to validate EarthCARE’s measurements using our ground measurement sites around the world.