Comparison of Radio Occultation Bending Angle and Refractivity Processed by Different Inversion Algorithms from Multi-Ro Missions

This paper presents the development of an independent algorithm at NOAA/STAR for processing radio occultation (RO) bending angle and refractivity data from RO observations explicitly designed for multi-GNSS RO missions. The primary aim is to understand the uncertainties introduced in the processing, from excess phase data to bending angle and refractivity profiles. This study investigates three algorithms that convert RO excess phases to bending angles. These three algorithms are full spectrum inversion (FSI), canonical transform type 2 (CT2), and phase matching (PM). The STAR-developed 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. A detailed comparison of bending angle and refractivity results generated by these three algorithms, explicitly focusing on COSMIC-2 and Spire data, is presented. The analysis highlights discrepancies and uncertainties inherent in bending angle and refractivity processing, providing valuable insights into the performance of each algorithm.