Upgrading an End-to-End Simulator for Aeolus to EPS-Aeolus

Abstract

On 28 July 2023, the fruitful operational era of the Aeolus satellite came to an end with the successful assisted re-entry carried out by the European Space Agency (ESA), marking the end of a period full of world firsts. Building on the success of Aeolus, a follow-up mission called EPS-Aeolus is being developed in collaboration between the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) and ESA with the aim to significantly improve numerical weather prediction based on near real-time observations. After the currently planned launch in 2034, EPS-Aeolus (EUMETSAT Polar System) will continue the wind speed and aerosol measurements of Aeolus based on its technological heritage: Emitting laser pulses at 355 nm and analysing the Doppler-shifted light backscattered from the atmosphere using two different interferometers to detect Rayleigh and Mie scattering from molecules and aerosols or clouds. However, the design of EPS-Aeolus is still under development, with significant changes to the instrument setup, including modifications to the laser, the beam path (switching to a bi-static setup instead of a transceiver), the detector and potentially the spectrometer for the Rayleigh channel. These upgrades aim to enhance the vertical (from 250 m to 125 m) and horizontal (from ≈90 km to ≈50 km) resolution, extend the vertical coverage into the stratosphere (from ≈30 km up to 40 km), and provide more accurate wind measurements (≈2–2.5 m/s random error) for an increased number of range-bins (66 instead of 24). As part of a “Doppler Wind Instrument Simulator Study” funded by EUMETSAT, the German Aerospace Center (DLR) is planning to update the existing End-to-End Simulator (E2S) configuration for Aeolus to carry out initial performance simulations for the future EPS-Aeolus satellite. By incorporating the instrument's detailed technical specifications and user-defined atmospheric conditions, the E2S generates Rayleigh and Mie signal data. Along with housekeeping and ephemeris data, the E2S produces output files in the same format as those from the satellite. This allowed a direct coupling of the E2S to the operational Level 0/1 processors and comparisons of simulation results with real measurements of Aeolus. Such successful comparisons support the plausibility of the performance simulated for EPS-Aeolus. We will outline the structure and capabilities of the existing E2S for Aeolus and thus provide an overview of the possibilities of the current “E2S – Level 0 / 1A / 1B” processing chain. Among others, this includes the simulation of the satellite’s behaviour, the laser transmission, the atmospheric state and ground characteristics, the reception path, the spectrometers, the detectors and finally the generation of Annotated Instrument Source Packet (AISP) products, which corresponds to the downlinked data received by the ground station. Having upgraded the E2S with respect to selected features of EPS-Aeolus, we are now able to simulate first EPS-Aeolus-like measurements.