# On the Feasibility of Interhemispheric Patch Detection Using Ground-Based GNSS Measurements
## 4 Results and Discussion
### The Feasibility of Patch Monitoring Using Ground-Based GNSS Receivers
In contrast to this, the distribution of GNSS measurements was in this case highly favorable, as it resulted in a clear depiction of high-density plasma on the dayside ionosphere. Figure 5 confirmed that the usefulness of ground-based GNSS data at the southern hemisphere is mostly restricted to polar cap area. Figure 6 clarifies the opposite situation with patches detected only in SWARM data (Figure 4c, 4:00-10:00 UT). As it was reported in previous investigations, this period was characterized by a deep depletion of plasma [47; 49]. Due to the same reason and northwardly-oriented IMF, the patches observed in the in situ data are much weaker, as depicted in the bottom panel of Figure 6. In this case, the solid black lines correspond to patch signatures according to PCP results. Looking at the results for elevation mask equal to 30\({}^{\circ}\), it is clear that GNSS and SWARM techniques sounded different parts of the ionosphere. Thus, the lack of consistency that is observed in Figure 4c is a consequence of the visualization method. On the other hand, this highlights the possible scenario wherein GNSS measurements do not capture the propagated structures. Taking into account the distribution of receivers, it is likely to occur for periods with the most data on the dusk or dawn sides. This effect is partly related to the equatorward orientation of GNSS signals that resulted from the applied elevation mask. Hence, the right top panel of Figure 6 demonstrates the results, including the low-elevated data (>15\({}^{\circ}\)). As one can expect, this improves the coverage of the polar area by GNSS measurements, and allows the detection of the first structure observed in SWARM data. Its signature for relative STEC values reaches up to six to seven TECu. The second patch was not identified with GNSS, which may be related to the still poor distribution of ground-based measurements, as well as the extremely weak enhancement in this case. According to the results of the PCP project, this structure met the foreground/background criterion, but the relative growth of plasma density was only at the level of 0.2 \(\times\) 10\({}^{5}\)/cm\({}^{3}\). The identification of such a low-density patch with GNSS seems to be questionable, and needs further investigation. Figure 5: The signatures of patches derived from GNSS and SWARM measurements. The top panel presents the distribution of relative STEC values as a function of magnetic local time (MLT) and AACGM latitude with two superimposed arcs of SWARM depicted with black dotted and solid lines. The bottom panel presents the corresponding temporal profiles of SWARM foreground plasma density. The strong enhancements of plasma density are marked with a solid black line in both panels. Summarizing the above, the relative STEC values can be treated as an alternative for current methods of polar patch detection. Taking into account the current distribution of GNSS receivers, the proposed methodology allows the identification and tracking of polar patches. On the other hand, the comparison of GNSS and SWARM data indicates that both of these techniques may not provide the complete ionospheric information. Thus, their integration seems to be an appropriate technique for more detailed study.