Comparing performance simulations for Aeolus and Aeolus-2

Kurzfassung

On August 22nd, 2018, the European Space Agency (ESA) launched its Earth Explorer satellite Aeolus, which carried the first wind lidar into space: ALADIN (Atmospheric LAser Doppler INstrument). This lidar emitted laser pulses at 355 nm and analysed the light, that was Doppler shifted and backscattered by the atmosphere, by using two different types of interferometers for the detection of Rayleigh and Mie scattering from molecules and aerosols or clouds, respectively. During its almost five years of operation Aeolus provided the first measurements of line-of-sight wind profiles between 0 - 25 km on a global scale and in near real time, which showed a significantly and positive impact on numerical weather prediction. On July 28th, 2023, ESA successfully performed an assisted re-entry of Aeolus, another world's first. Based on the success of Aeolus-1, a follow-up mission called Aeolus-2 (or EPS-Aeolus at EUMETSAT) is currently being planned in cooperation between EUMETSAT and ESA. The design of Aeolus-2 is still under development, with major modifications envisaged for the instrument setup, including the laser, the beam path (bi-static instead of transceiver) and the detector. This shall enable Aeolus-2 to provide an improved vertical (up to 125 m) and horizontal (10 km for the Mie channel) resolution, an extended coverage higher into the stratosphere (> 30 km with the Rayleigh channel) and more precise wind measurements (< 2.5 m/s random error in the Troposphere). In a -Doppler Wind Instrument Simulator Study- funded by EUMETSAT the German Aerospace Center (DLR) updates the configuration of the existing End-to-End Simulator (E2S) for Aeolus-1 to carry out initial performance simulations representative of the future Aeolus-2 satellites. By considering the detailed technical characteristics of the instrument as well as user defined atmospheric conditions, the E2S produces Rayleigh and Mie signal data. Together with albedo and digital elevation model information as well as housekeeping and ephemeris data the E2S then creates output files with the same format as provided by the Aeolus-1 satellite. This allows a direct coupling of the E2S to the operational Level 0/1 processors and comparisons of simulation results against measurements of Aeolus-1. Our study also evaluated the impact of replacing the Fabry-Pérot interferometer, as used for Aeolus' Rayleigh channel, with a double-field compensated Michelson interferometer (DMI). We will explain the structure and capabilities of the E2S and name assumptions and limitations of our approach. The primary goal of the study is to pave the way towards a performance simulator for Aeolus-2. As a first step, this includes achieving consistency between simulation and measurement for Aeolus-1 in terms of the atmospheric signal levels and the wind random error. We will present comparisons that oppose real measurements by Aeolus-1 to respective simulations for Aeolus-1 as well as for Aeolus-2.