Assessment of storm-time ionospheric electron density measurements from Spire Global CubeSat GNSS radio occultation constellation

Spire Global's CubeSats has been collecting global navigation satellite system ionospheric radio occultation (RO) measurements since November 2019. This study presents a comprehensive evaluation of storm-time ionospheric electron density measurements derived from Spire precise orbit determination (POD) antenna by comparing them with measurements obtained from digisonde, incoherent scatter radar (ISR), and the constellation observing system for meteorology, ionosphere, and climate 2 (COSMIC2) mission during February 2020-December 2021. Results showed electron density profiles (EDPs) retrieved from Spire POD antenna are in general agreement with those from digisonde, ISR, and COSMIC2 RO observations, although Spire-retrieved EDPs sometimes are noisier than others. Spire-derived F2 layer peak density (NmF2) and peak height (hmF2) agree well with collocated measurements from digisonde and COSMIC2. The good performance of Spire-derived ionospheric parameters provides a baseline reference for subsequent merged observations from POD and RO antennas and suggests that low-cost CubeSats can provide reliable ionospheric measurements to significantly contribute to global ionospheric monitoring.