Validating the Aeolus wind measurement performance: After three successful airborne validation campaigns over Europe and Iceland, this time the focus was on the Aeolus performance in the tropics. The global wind information is key for accurate numerical weather prediction, which the Aeolus data has already demonstrated, especially in regions where other wind data sources are sparse, like in the tropics.
DLR (front) and SAFIRE (back) Falcons on Sal Airport. Credit: DLR/C. Lemmerz (CC BY-ND-NC 3.0)
The DLR team on Sal. Credit: DLR (CC-BY3.0)
For validating the Aeolus wind products, the IPA team again installed two downward-looking Doppler Wind Lidars (DWL) aboard the DLR Falcon and prepared for coordinated flights underneath the satellite measurement track. The ALADIN Airborne Demonstrator (A2D) measures wind in clear air (Rayleigh) as well as in cloud and aerosol (Mie) conditions along the line of sight (LOS) with the same two-channel instrument design as Aeolus. In parallel, reference measurements are performed by the aerosol-scattering-sensitive, scanning 2-µm DWL that provides the wind vector profile with high accuracy and precision. Both DWLs allowed to explore relevant limits in operations and algorithms for Aeolus already during measurement campaigns on the trail of the wind (e.g. WindVal, NAWDEX) before its launch in mid 2018.
Delayed by more than a year due to the COVID-19 pandemic, the IPA team supported by eleven members of the DLR Flight Experiments facility finally flew to Sal, Cape Verde in September 2021, to conduct AVATART (Aeolus Validation Through Airborne LidaRs in the Tropics). AVATART is the DLR contribution to the international Joint Aeolus Tropical Atlantic Campaign (JATAC). Organized by ESA and NASA, JATAC combines several airborne participants, including the French SAFIRE Falcon 20 aircraft and the NASA DC-8 (on US Virgin Islands), with ground measurements located on a neighboring island.
Among the various goals of JATAC, AVATART has a clear focus on wind measurements. With its unique combination of the 2-µm reference DWL and the A2D, it is studied how the data coverage, accuracy and precision of the Aeolus wind products are influenced by the tropical atmospheric conditions in the region
Preliminary data analysis reveals that the A2D measured significantly more Mie winds than Aeolus within the dust-laden Saharan Air Layer (SAL) below 6 km. Instead, the Aeolus processor often detected clear atmosphere Rayleigh winds of decreased quality within the SAL. A2D signals confirm that a more appropriate discrimination of Mie and Rayleigh winds is principally possible with the Aeolus type instrument.
Broken clouds embedded in Saharan dust, seen from the Falcon just before Aeolus passed. In such conditions, accurate wind measurements are demanding for Aeolus. Credit: DLR/C. Lemmerz (CC BY-ND-NC 3.0)
The analysis now focusses on detecting and understanding such error sources, to derive possibilities for improving the Aeolus algorithms. This has the potential to increase the Aeolus data quality both during its remaining lifetime and for the reprocessing of the Aeolus mission results since 2018. Further ahead the findings, methods and lessons learned from the AVATART campaign and JATAC will pave the way for the success of the upcoming European EarthCARE mission and potential Aeolus follow-on satellites.