## 6 Conclusions, Discussions, and Potential Applications  
Ref. [1] has summarized the potential applications using COSMIC-2 for climate and NWP, and space weather. Before applying COSMIC-2 data for science studies and operational applications, it is critically important to quantify COSMIC -2 data quality carefully. This study uses the currently most accurate radiosonde observations obtained from Vaisala RS41 to assess the quality of neutral atmospheric profiles derived from COSMIC-2 signals. In general, the COSMIC-2 data quality in terms of stability, precision, accuracy, and uncertainty of the accuracy is very compatible with those from COSMIC-1. The conclusions we reach are as follows:  
1. Spatial and temporal coverage. COSMIC-2 has a different spatial coverage compared with that of COSMIC and other RO missions. COSMIC-2 is a six-satellite constellation mission. With a 24-degree inclination at 720 km latitude, COSMIC-2 occultations are distributed within the region from 45\({}^{\circ}\) N and 45\({}^{\circ}\) S. The uniform temporal coverage occurs mainly over 30\({}^{\circ}\) N and 30\({}^{\circ}\) S. COSMIC-2 provides an average of about three to five soundings per day in each 500 \(\times\) 500 km\({}^{2}\) box in subtropics from 35\({}^{\circ}\) N to 35\({}^{\circ}\) S.  
2. Penetration. CDAAC inversion procedures determine the COSMIC-2 penetration depth (i.e., the cut off height). The penetration height may vary when different inversion algorithms are applied. The mean L1 COSMIC-2 SNR is equal to 1200 \(\
u\)/\(\
u\), where that for both COSMIC and KOMPSAT-5 is about 700 \(\
u\)/\(\
u\). With a higher mean SNR than all other RO missions (i.e., COSMIC, \begin{table}
\begin{tabular}{c c} \hline \hline
**L1 SNR Range** & **Mean Difference (stds) for Water Vapor from the Surface to 5 km Altitude (g/kg)** \\ \hline
0–500 \(\
u\)/\(\
u\) & \(-\)1.34 (2.51) \\ \hline
500–1000 \(\
u\)/\(\
u\) & \(-\)1.17 (2.63) \\ \hline
1000–1500 \(\
u\)/\(\
u\) & \(-\)1.33 (2.65) \\ \hline
1500–2000 \(\
u\)/\(\
u\) & \(-\)0.93 (2.55) \\ \hline \(>\)2000 \(\
u\)/\(\
u\) & \(-\)1.52 (2.62) \\ \hline \end{tabular}
\end{table} 
Table 4: The mean COSMIC-2–RS41 difference of the water vapor profiles from the surface to 5 km altitude for five SNR groups. Figure 14: Similar to Figure 13 but for COSMIC-2 water vapor profiles from the surface to 5 km altitude for different SNR groups. KOMPSAT-5, MetOp-A, -B, and C, etc. ), more than 85% of COSMIC-2 data penetrate deeper than 1 km altitude, where about 80% of COSMIC data penetrate deeper than that height. The penetration height for COSMIC-2 (and other RO missions) is deeper over drier regions (usually in mid-latitude winter) than that over the tropical region (and mid-latitude summer). 3. Precision. Using co-planar measurements in the early phase of the COSMIC-2 mission while two COSMIC-2 flight modules are within 1200s and a distance separation at the ray tangent point of about 300 km apart, we can quantify the precision of COSMIC-2 temperature, water vapor, and refractivity profiles. COSMIC-2 fractional refractivity precision varies from \(-\)0.2% to 0.2% below 8 km and is within +/\(-\) 0.1% between 8 km and 30 km altitude. The mean precision for COSMIC-2 temperature is within 0.2 K, between 8 km and 35 km. The precision for the COSMIC-2 water vapor mixing ratio is within 0.15 g/kg below 5 km. COSMIC's precision is within less than 0.05 K for temperature and 0.35 g/kg for water vapor from the surface to 30 km, respectively. The reason that COSMIC-2's precision is slightly larger than those of COSMIC may be partly owing to the paired COSMIC-2 data are collected with larger time-spatial criteria (1200 s and 300 km apart) than those of COSMIC pairs for two receivers (within 5 s and 10 km apart [42]). 4. Stability. With the SI-traceable time delay measurements, the RO neutral atmospheric profiles derived from time delay and carrier phase measurements are also very stable [42].