Aeolus Performance Monitoring at DLR - From Satellite Level to Airborne Validation

Abstract

Already in the decade before, various ground and airborne pre-launch validation campaigns had been performed in support of the Aeolus operations and processor development. An integral part of the early success of the mission was the deployment of the ALADIN Airborne Demonstrator (A2D), a prototype of the ALADIN Doppler Wind Lidar (DWL) instrument on-board Aeolus. With its high technological commonality, it allowed to study Aeolus-specific lidar topics under various atmospheric conditions already before launch. In addition, the scanning, coherent 2-μm DWL acted as a high-accuracy reference by providing wind vector profiles for the A2D and Aeolus validation. Airborne measurements were performed with the two instruments operated in parallel on the DLR Falcon research aircraft in a downward looking configuration. The comprehensive operational, technological and algorithm knowledge established at DLR during these pre-launch activities laid the basis for a twofold Aeolus performance monitoring, implemented to support the mission. Firstly, performance-relevant instrument parameters of the laser and receiver optics as well as the detector signals evolution for the internal reference and atmospheric path were monitored and reported on a regular basis. Additionally, special operations for tests of the Aeolus lasers and instrument alignment were supported, both by applying the tools derived during the pre-launch period and with newly developed performance indicators. The second monitoring activity was covered by four post-launch airborne validation campaigns with a focus on the Aeolus wind product. Deploying the two DWLs onboard the Falcon, coordinated flights along a total distance of 26,000 km under the Aeolus track were performed in different geographical regions and during the main operational phases of the mission until September 2021. The collocated A2D and 2-μm DWL wind observations not only reflect the evolution of the error characteristics during each mission state, but also provide valuable recommendations for the optimization of the Aeolus wind retrieval and related quality control algorithms. This contribution gives an overview of the Aeolus in-orbit instrument performance evolution and related results of the four airborne validation campaigns.