EarthCARE's cloud profiling radar antenna pointing correction using surface Doppler measurements

Abstract. The Earth Cloud Aerosol and Radiation Explorer (EarthCARE) mission, a joint effort between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), aims to advance our understanding of aerosols, clouds, precipitation, and radiation using a comprehensive payload of active and passive sensors. A key component of the payload is the 94 GHz cloud profiling radar (CPR), which provides the first-ever Doppler velocity measurements collected from space. Accurate knowledge of the CPR antenna pointing is essential for ensuring high-quality CPR Doppler velocity measurements. This study focuses on the geolocation assessment and antenna mispointing corrections during EarthCARE's commissioning phase and beyond, using Earth's surface Doppler velocity measurements collected over the first 9 months of the mission. While the instrument footprint is proven to be properly geolocated within about 100 m, surface Doppler velocity observations reveal mispointing trends influenced by solar illumination cycles and thermoelastic distortions on the antenna. Correcting these effects significantly reduces biases, ensuring better Doppler velocity measurements, essential for understanding cloud microphysics and dynamics. The results, validated through the analysis of Doppler velocities in ice clouds, underline the critical role of pointing corrections for the success of the EarthCARE mission.