Reducing radio occultation uncertainty using high-rate GNSS satellite clock estimation

Global navigation satellite systems (GNSS) radio occultation (RO) is a satellite remote sensing technique that uses GNSS measurements collected on low-Earth orbiting satellites to profile the Earth’s neutral atmosphere and ionosphere with high vertical resolution and global coverage. A theoretical study has shown that high-rate estimation of GNSS satellite clock offsets is critical to the retrieval of bending angles in GNSS RO processing, particularly for GLONASS. Inspired by this study, we have generated high-rate GNSS satellite clock products at 2 s intervals using the GINAN GNSS software, based on globally-distributed ground GNSS stations. Then we perform RO bending angle retrievals for the COSMIC-2 mission using one week of our clock products. The fundamental noise of GLONASS RO has dropped by 34% when using 2 s clock products compared to 30 s clock products. Furthermore, the uncertainty of the bending angle estimation in GPS + GLONASS RO has reached <1 × 10⁻⁶ radian, an ultra-precise level that allows the RO technique to monitor weather and space weather with a higher sensitivity.