The way to a performance simulator for EPS-Aeolus

Kurzfassung

On August 22nd, 2018, the European Space Agency (ESA) launched its Earth Explorer satellite Aeolus carrying the first wind lidar into space: ALADIN (Atmospheric LAser Doppler INstrument) emitted laser pulses at 355 nm and analysed the Doppler shifted light backscattered by the atmosphere using two different types of interferometers for detecting Rayleigh and Mie scattering from molecules and aerosols or clouds, respectively. During its almost five years of operation Aeolus provided the first measurements of vertical wind profiles between 0-25 km on a global scale and in near real time, which showed significant 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, a follow-up mission called EPS-Aeolus is planned in cooperation between EUMETSAT and ESA. The design of EPS-Aeolus is still under development, with major modifications to the instrument setup, including the laser, the beam path (bi-static instead of transceiver) and the detector. This shall enable EPS-Aeolus to provide an improved vertical (up to ≈100 m) and horizontal (≈50 km) resolution, a higher coverage into the stratosphere (≈30 km) and more precise wind measurements (≈2 – 2.5 m/s random error). 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 to carry out initial performance simulations representative of the future EPS-Aeolus 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 housekeeping and ephemeris data the E2S then creates output files with the same format as provided by the satellite. This allows a direct coupling of the E2S to the operational Level 0/1 processors and comparisons of simulation results against real measurements of Aeolus. Our study also evaluates the impact of replacing the Fabry-Pérot interferometer, as used for Aeolus’ Rayleigh channel, with a double-field compensated Michelson interferometer (DMI), which is planned as an option for EPS-Aeolus. In this context, the effect of so-called “crosstalk”, i.e. the sensitivity of the Rayleigh channel to spectrally narrow Mie-type backscatter signal from aerosols or clouds, is investigated. If not properly corrected, such crosstalk of Mie signal will result in significant systematic wind errors on the Rayleigh channel. We will explain the structure and capabilities of the E2S and name assumptions and limitations of our approach. We will present first results from simulations compared to real measurements of Aeolus and provide a general assessment of the performance of a DMI.