Recently, the NOAA has included GNSS (Global Navigation Satellite System) Radio Occultation (RO) data as one of the crucial long-term observables for weather and climate applications. To include more GNSS RO data in its numerical weather prediction systems, the NOAA Commercial Weather Data Pilot program (CWDP) started to explore the commercial RO data available on the market. After two rounds of pilot studies, the CWDP decided to award the first Indefinite Delivery Indefinite Quantity (IDIQ) contract to GeoOptics and Spire Incs. in 2020. This study examines the quality of Spire RO data products for weather and climate applications. Spire RO data collected from commercial CubeSats are carefully compared with data from Formosa Satellite Mission 7–Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2), the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5), and high-quality radiosonde data. The results demonstrate that, despite their generally lower Signal-Noise-Ratio (SNR), Spire RO data show a pattern of lowest penetration height similar to that of COSMIC-2. The Spire and COSMIC-2 penetration heights are between 0.6 and 0.8 km altitude over tropical oceans. Although using different GNSS RO receivers, the precision of Spire STRATOS receivers is of the same quality as those of the COSMIC-2 TriG (Global Positioning System—GPS, GALILEO, and GLObal NAvigation Satellite System—GLONASS) RO Receiver System (TGRS) receivers. Furthermore, the Spire and COSMIC-2 retrieval accuracies are quite comparable. We validate the Spire temperature and water vapor profiles by comparing them with collocated radiosonde observation (RAOB) data. Generally, over the height region between 8 km and 16.5 km, the Spire temperature profiles match those from RS41 RAOB very well, with temperature biases of <0.02 K. Over the height range from 17.8 to 26.4 km, the temperature differences are ~−0.034 K, with RS41 RAOB being warmer. We also estimate the error covariance matrix for Spire, COSMIC-2, and KOMPSAT-5. The results show that the COSMIC-2 estimated error covariance values are slightly more significant than those from Spire over the oceans at the mid-latitudes (45°N–30°N and 30°S–45°S), which may be owing to COSMIC-2 SNR being relatively lower at those latitudinal zones.

Recently, NOAA has included GNSS (Global Navigation Satellite System) Radio Occultation (RO) data as one of the crucial long-term observables for weather and climate applications. To include more GNSS RO data in the numerical weather prediction system, the NOAA Commercial Weather Data Pilot program (CWDP) started to explore the commercial RO data available on the market. After two rounds of pilot studies, the CDWP decided to award the first Indefinite Delivery Indefinite Quantity (IDIQ) contract to GeoOptics and Spire Incs. in 2020. This study examines the quality of Spire data products for weather and climate applications. Spire RO data are collected from commercial CubeSats through careful comparison with the data from Formosa Satellite Mission 7–Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2), ERA-5, and high-quality radiosonde data. The results demonstrated that although with lower Signal-Noise-Ratio (SNR) in general, the pattern of the lowest penetration height for Spire is similar to those for COSMIC-2. The Spire and COSMIC-2 penetrate heights are between 0.6 and 0.8 km altitude at the tropical oceans. Although using different GNSS RO receivers, the precision of Spire STRASP receivers is of the same quality as those of COSMIC-2 Global Positioning System - GPS, GALILEO, and GLObal NAvigation Satellite System – GLONASS (TGRS) receivers. The retrieval accuracy from Spire is very compatible with those from COSMIC-2. We validated Spire temperature and water vapor profiles by comparing them with collocated radiosonde data. Generally, over the height region between 8 km and 16.5 km, the Spire temperature profiles match those from RS41 RAOB very well with temperature biases < 0.02 K. Over the height range from 17.8 to 26.4 km, the temperature differences are ~-0.034 K with RS41 RAOB being warmer. We also estimated the error covariance matrix for Spire, COSMIC-2, and KOMPSAT-5. Results showed that the COSMIC-2 estimated error covariance values are slightly more significant over the oceans at the mid-latitudes (45oN-30oN and 30oS-45oS), which may also be owing to COSMIC-2 SNR being lower at those latitudinal zones.

Global Navigation Satellite System (GNSS) radio occultation (RO) has evolved into a heterogeneous multi-mission observing system that combines national, international partner, and commercial constellations. This review and outlook synthesize NOAA/STAR assessments of GNSS RO commercial data, including Spire and PlanetiQ, and compare their quality with those of national missions, COSMIC-2, MetOp, and other missions. We emphasize the results in the neutral atmosphere. To examine heterogeneous multiple RO missions, we organized the comparisons along a pathway from (i) orbit and viewing geometry through antenna gain and received signal, (ii) examining their signal-to-noise ratio (SNR) and penetration, (iii) quantifying the phase quality, retrieval bias and uncertainty, (iv) demonstrating their impacts on numerical weather prediction (NWP), and climate and environmental applications. The reviewed comparisons show that higher SNR generally improves tracking and lower-tropospheric penetration but does not by itself remove biases and uncertainty arising from water-vapor irregularity, multipath, super-refraction, departures from spherical symmetry, or processing choices. Spire and PlanetiQ retrievals are broadly compatible with COSMIC-2 and international missions in the principal atmospheric layers, and their additional profiles improve spatiotemporal sampling and provide incremental value for global and tropical-cyclone prediction. For long-term environmental records, however, operational usefulness is not sufficient: common processing, inter-mission stability assessment, sampling correction, and mission-specific uncertainty characterization are required. Multi-mission RO observations support upper-troposphere and lower-stratosphere temperature records, tropospheric water-vapor variability and trend analyses, and planetary-boundary-layer height estimates when these conditions are met. The synthesis yields an application-conditioned evaluation framework that separates signal quality, retrieval quality, usable observation yield, sampling complementarity, and downstream impact. The principal outlook priorities are uncertainty-aware quality control and error specification, improved treatment of super-refraction and lower-tropospheric retrievals, sustained multi-mission reprocessing and intercomparison, and observing-system design that balances measurement quality with coverage.

Global Navigation Satellite System (GNSS) radio occultation (RO) has evolved into a heterogeneous multi-mission observing system that combines national, partner, and commercial constellations. This review and outlook synthesize NOAA/STAR assessments of GNSS RO commercial data, including Spire and PlanetiQ, and compares their quality with those of national missions, COSMIC-2, MetOp, and other missions. We emphasize the results in the neutral atmosphere. To examine heterogeneous multiple RO missions, we organized the comparisons along a pathway from i) orbit and viewing geometry through antenna gain and received signal, ii) examining their signal-to-noise ratio (SNR) and penetration, iii) quantifying the phase quality, retrieval bias and uncertainty, iv) demonstrating their impacts on numerical weather prediction (NWP), and climate and environmental applications. The reviewed comparisons show that higher SNR generally improves tracking and lower-tropospheric penetration but does not by itself remove biases and uncertainty arising from water-vapor irregularity, multipath, super-refraction, departures from spherical symmetry, or processing choices. Spire and PlanetiQ retrievals are broadly compatible with COSMIC-2 and partner missions in the principal atmospheric layers, and their additional profiles improve spatiotemporal sampling and provide incremental value for global and tropical-cyclone prediction. For long-term environmental records, however, operational usefulness is not sufficient: common processing, inter-mission stability assessment, sampling correction, and mission-specific uncertainty characterization are required. Multi-mission RO observations support upper-troposphere and lower-stratosphere temperature records, tropospheric water-vapor variability and trend analyses, and planetary-boundary-layer height estimates when these conditions are met. The synthesis yields an application-conditioned evaluation framework that separates signal quality, retrieval quality, usable observation yield, sampling complementarity, and downstream impact. The principal outlook priorities are uncertainty-aware quality control and error specification, improved treatment of super-refraction and lower-tropospheric retrievals, sustained multi-mission reprocessing and intercomparison, and observing-system design that balances measurement quality with coverage.