Atmospheric and ionospheric remote sensing using GNSS: FORMOSAT-7 system performance and lessons learned after five years mission life in orbit

The FORMOSAT-7/COSMIC-2 (F7C2) is a joint collaboration program between Taiwan and US to continue the provision of next-generation Global Navigation Satellite System (GNSS) Radio Occultation (RO) data to the global users Numerical Weather Prediction (NWP). The six F7C2 satellites were successfully launched into a 24 deg inclination low Earth orbit on June 25, 2019. The F7C2 mission aims to collect atmospheric and ionospheric remote sensing data (soundings) globally through a constellation system of six satellites, providing high temporal resolution and high data quality. The retrieved atmospheric and ionospheric GNSS-RO data have been freely available online to the users’ community since shortly after the completion of neutral atmosphere Initial Operational Capability (IOC) in March 2020 and Full Operational Capability (FOC) in September 2021, respectively. The F7C2's atmospheric and ionospheric occultation RO requirements are at least 4,000 profiles per day, and after May 2021, the atmospheric and ionospheric occultation RO profiles have reached more than 5,500 and 4,000 average profiles per day, respectively. Atmospheric and ionospheric occultation RO profiles accumulated by F7C2 (as-of-Oct. 15, 2024), the total number of atmospheric occultations is 9,813,366 and the total number of ionospheric occultations is 7,035,981. This paper provides an overview of the F7C2 mission operational telemetry trends after five years of six-satellite in-orbit, demonstrating good system performance in collecting next-generation GNSS RO data and provide the lessons learned after 5 years of operations in space.