Assessing Retrieved Temperature Profile Quality and Consistency in Spire and COSMIC-2 Radio Occultation via Comparisons with NOAA-20 ATMS and Radiosonde Measurements

Global Navigation Satellite System (GNSS) radio occultation (RO) provides accurate and precise information about atmospheric temperature, water vapor, and pressure. These RO retrievals are essential for numerical weather prediction (NWP) and climate research. Efforts have been directed toward building infrastructure to acquire more RO data with uniform time and space distribution for NWP and climate studies applications. One notable initiative is the NOAA Commercial Data Program (CDP), which procures Commercial Weather Data (CWD) from commercial providers like Spire Global Inc. To ensure the consistency and reliability of Spire Global Inc.'s data with other RO missions, such as COSMIC-2, it's imperative to assess the accuracy and uncertainty of their measurements.

This study focuses on evaluating the consistency between temperature profiles in the neutral atmosphere obtained from Spire and COSMIC-2 RO data, as well as from Advanced Technology Microwave Sounder (ATMS) measurements and radiosonde data. The analysis encompasses Spire and COSMIC-2 wet temperature profiles processed by the University Corporation for Atmospheric Research (UCAR) from September 7, 2021, to October 31, 2022. We compare temperature differences between Spire and COSMIC-2 RO data with collocated NOAA-20 ATMS and RS41 radiosonde measurements. The consistency between Spire and COSMIC-2 data via ATMS and radiosonde measurements is also examined. By carrying out Community Radiative Transfer Model (CRTM) simulations with RO retrievals as inputs, the brightness temperatures (BT) from NOAA-20 ATMS observations are compared with RO-simulated BTs for ATMS CH07 to CH14 and CH19 to CH22 sounding channels over the ocean. The differences between Spire and COSMIC-2 BTs and ATMS observations are less than 0.07 K for CH07-14 and 0.20 K for CH19-22. The study further explores the agreement between Spire and COSMIC-2 to RS41 radiosonde observations (RAOB). Above 0.2 km altitude, RS41 RAOB data agrees well with both Spire and COSMIC-2 temperature profiles, demonstrating a temperature difference below 0.13 K. In addition, we also studied the dependence of the agreement between Spire and COSMIC-2 on latitude intervals, local times, and signal-to-noise ratios (SNRs) by using ATMS data as the reference. Our comparisons demonstrated that the Spire RO data is comparable with COSMIC-2, even though COSMIC-2 has a higher SNR.