Consistent Processing of COSMIC-2, COSMIC-1, and Commercial CubeSat RO Missions Using Full Spectrum Inversion Algorithm

The importance of Global Navigation Satellite System (GNSS) Radio Occultation (RO) data continues to grow due to its vital contributions to weather forecasting and climate analysis. Extracting accurate excess phase and bending angle information from GNSS RO signals remains a formidable challenge, given the intricate atmospheric conditions and the complexity of multi-GNSS signals. The expanding landscape of RO missions, including small commercial satellites like Spire, GeoOptics, and PlanetIQ, alongside established ones such as Metop-B/C, COSMIC-2, and Sentinel-6, has led to a diverse array of RO receivers deployed in space, each with varying quality. Multiple independent GNSSs are equipped with transmitter modules and clocks that transmit signals at different carrier frequencies. Similarly, multiple low Earth orbit (LEO) satellites exist, ranging from small cubes to dedicated RO satellites. These multiple transmitter-receiver combinations make RO processing challenging. While processing algorithms share a common framework across missions, the unique characteristics of each sensor and mission-specific demands require tailored processing approaches and specialized interfacing software.

The NOAA Center for Satellite Applications and Research (STAR) has developed robust GNSS RO science and data center capabilities. The STAR-developed full spectrum inversion (FSI) algorithm has been fully integrated into the Radio Occultation Processing Package (ROPP) version 10.0. This integration provides users with an alternative to wave optics and geometry optics through configurable settings. This paper outlines the consistent processing of RO bending angle and refractivity data from multi-GNSS RO missions, including COSMIC-1, COSMIC-2, Spire, and PlanetIQ. The main objective is understanding the uncertainties introduced during processing, from excess phase data to bending angle and refractivity profiles. We will present the validation results for the RO data quality, penetration height evaluation, and bending angle uncertainties due to the choice of signal-to-noise ratios (SNR) cut-off height.

Additionally, we will compare the stability among COSMIC-1, COSMIC-2, Spire, and PlanetIQ. The analysis highlights overall consistency and investigates remaining discrepancies, emphasizing the uncertainties inherent in bending angle and refractivity processing. This provides valuable insights into the performance of each mission, which are vital for explaining the time series results from RO retrieval in climate applications.