## 4 Results and Discussion
### PlanetQi-NWP Models Comparison
#### 4.3.2 PlanetIQ-ECMWF Model Comparison  
Figure 18 illustrates a comprehensive comparison of the critical variables: pressure, refractivity, temperature, and WVP, between the PlanetIQ and ECMWF model profiles for the entire study period. The results provide a full overview of the differences, expressed in mean difference, maximum difference, maximum difference percentage, and RMSE metrics. For Pressure, the maximum difference is 3.0875, with a corresponding maximum difference percentage of 0.4%. The mean difference is \(-\)0.16, with a maximum RMSE of 25.6. The altitude of the maximum mean difference is 25.2 km, while the maximum RMSE occurs at an altitude of 3.0 km, constituting a mean difference percentage at the maximum RMSE of \(-\)0.4%. In terms of refractivity, the maximum difference is 1.0, accompanied by a maximum difference percentage of 0.5%. The mean difference is \(-\)0.04, with a maximum RMSE of 8.8284. The altitude of the largest mean difference is 12.5 km, while the maximum RMSE occurs at 3.0 km, with a mean difference percentage of \(-\)0.5% at the maximum  
Figure 18: Mean diff., mean diff.%, and RMSE between PlanetIQ and ECMWF model profiles for all variables. RMSE. Moreover, in the [38] study, which compared GNOS/FY-3C refractivity data with COSMIC and MetOp/GRAS radio occultation data, it was determined that GNOS/FY-3C meets design requirements for accuracy and precision up to 30 km altitude. The study reported a mean bias of approximately \(-0.09\) (\(-0.04\%\)) in refractivity up to 46 km altitude, with an average standard deviation of approximately 1.81 (1.26%). These findings affirm the reliability and utility of GNOS/FY-3C as a valuable data source for global numerical weather prediction. Temperature differences exhibit a maximum difference of 0.2 \({}^{\circ}\)C and a maximum difference percentage of 10.9%. The mean difference is \(-0.01\), with a maximum RMSE of 2.7 \({}^{\circ}\)C. The altitude of the maximum mean difference is 32.8 km, whereas the maximum RMSE occurs at 3.0 km, with a mean difference percentage of 10.9% at the maximum RMSE. The research conducted by [12] provided valuable insights, which are consistent with the present findings, into the accuracy and reliability of temperature profiles derived from the STAR system. Their validation study revealed that temperature differences between STAR-RS41 profiles remained remarkably consistent, with variances within a narrow range of a few tenths of 1 K across altitudes spanning from 8 km to 30 km. Moreover, the standard deviation associated with these temperature variations fell between 1.5 and 2 K, indicating a high level of precision in the derived temperature data. Ref. [39] also compared temperature measurements from COSMIC-2 radio occultations with Vaisala RS41 and RS92 radiosonde observations. They found minimal temperature biases between the UCAR and NOAA/STAR algorithms and radiosonde data above 12.5 km. However, differences arose in the 8-11 km height range, with a net difference of \(\sim\)0.1-0.2 K, primarily due to variations in the 1 DVAR retrieval algorithms' treatment of a priori models. The study underscores the importance of such comparisons for refining temperature measurement accuracy. For WVP, the maximum difference is 0.04 mb, with a maximum difference percentage of 2.7%. The mean difference is \(-0.004\) mb, with a maximum RMSE of 0.8 mb. The altitude of the maximum mean difference is 8.0 km, while the maximum RMSE occurs at 3.0 km, with a mean difference percentage at the maximum RMSE of \(-1.2\%\). Figure 19 illustrates the percentage difference between the PlanetIQ and ECMWF profiles at 3 km altitude across various variables throughout the study duration. The pressure difference remains within \(\pm 0.2\%\), with minor deviations in limited areas globally. Notably, there is a marginal increase in the southern pole, indicating a more favorable agreement with the ECMWF model in terms of pressure differences compared to the GFS model.