## 7 Conclusions and Future Work  
Recently, the NOAA included GNSS RO data as one of the crucial long-term observables for weather and climate applications, just as those from IR and MW measurements. To include more GNSS RO data in the NWP system, the NOAA CWDP program started to explore the commercial RO data available on the market. CWDP awarded the first IDIQ contract to GeoOptics and Spire Incs. in 2020. Both GeoOptics and Spire RO data were collected from commercial CubeSats. Ref. [32] examined the GeoOptics data quality. This study examined the specific quality of the Spire data products during the DO3 and DO4 periods (from 8 September 2021 to 16 January 2023) for climate and weather applications. We carefully examined the Spire data's penetration, precision, stability, and accuracy. We also quantified the Spire BA vertical error uncertainty (the diagonal terms in the error covariance matrix), which is crucial for the RO NWP through DA. We reaches the following conclusions. 1. The spatial and temporal coverage. Spire had close to 30 satellites at LEO orbits during DO3 and DO4. Although the complete global Spire RO occultation was around 20 K per day during the performance periods, the CWDP purchased about 3000 Spire occultation profiles per day during DO3 and 5500 Spire occultation profiles per day in DO4. While COSMIC-2 has an inclination angle of 24\({}^{\circ}\), Spire is in the Sun-synchronized orbits. While Spire data cover the globe and are distributed relatively evenly across all latitudes, COSMIC-2 observations can cover all latitudes within [45\({}^{\circ}\)N, 45\({}^{\circ}\)S]. Spire has observations peaking local time ranges in 2-3, 9-10, 14-15, and 21-22, while the KOMPSAT5 observation peaking local times are located at 6 and 18, and COSMIC-2 observations cover all local times. 2. The effect of the SNR on Spire data penetration. The lowest penetration height is an essential indicator of RO data quality. The lowest penetration height of RO tracking is usually related to the data's SNR and the atmosphere's dryness. Although with a lower SNR in general, the pattern of the lowest penetration height for Spire was similar to that for COSMIC-2. The Spire and COSMIC-2 penetration heights were from around a 0.6 to 0.8 km altitude over tropical oceans. We also compared the lowest penetration height of 80% of the total data for different RO missions in different latitudinal zones. GeoOptics and Spire had lower penetration heights (for 80% of the total data) than COSMIC-2 in the latitudinal zones of [30\({}^{\circ}\)S, 45\({}^{\circ}\)S] and [45\({}^{\circ}\)N, 30\({}^{\circ}\)N]. This may be owed to COSMIC-2's SNR being lower in the latitudinal zones of [30\({}^{\circ}\)S, 45\({}^{\circ}\)S] and [45\({}^{\circ}\)N, 30\({}^{\circ}\)N]. 3. The Spire data precision and stability. We used the Spire-Spire SRO pairs to quantify the Spire precision for the bending angle, dry temperature, and water vapor mixing ratio. The results showed that the mean differences were very close to zero from the surface to a 40 km altitude for all three physical quantities. The standard deviations from the bending angle, dry temperature, and water vapor mixing ratio were similar to those from other RO missions, such as COSMIC-2 and COSMIC-1. We also compared the fractional mean BA difference for Spire S124 and S120 from the surface to a 40 km altitude, but separated with GPS, GLONASS, and GALILEO, respectively. Although the SNR ranges from different emitters were different, the mean differences for GPS, GLONASS, and GALILEO were all close to zero with STDs of 1.81, 1.78, and 1.78, respectively. We also compared the precision of COSMIC-1 (SRO pairs collected from 2006) and COSMIC-2 (SRO pairs collected from 2021) with those from Spire (SRO pairs collected from 2022). All the comparisons were within [45\({}^{\circ}\)N,45\({}^{\circ}\)S]. We found that the COSMIC-2 STDs over mid-latitudes were slightly more significant than those from Spire, which may be owed to their lower SNR over the same regions.