# Designation of the Quality of EGNOS+SDCM Satellite Positioning in the Approach to Landing Procedure
## 3 Research Experiment
Table 1 shows the results of VTEC parameter with time resolution of 1 h based on IONEX (IONosphere map EXchange) product from the Center for Orbit Determination in Europe (CODE) [70]. The VTEC parameter varied from 9.2 TECU (Total Electron Content Unit) to 22.6 TECU during the test flight. The highest VTEC value was at 12:00 and the lowest at 07:00 GPST. As the article analyses the phases of landing approach and landing, further sections of the paper will focus on these stages of flight. In order to determine the quality of the Multi-SBAS satellite positioning during the approach to landing, the observations and GNSS navigation data recorded from 11:38:31 h (41,911 s) to 11:55:59 h (42,959 s) according to system time GPST were used. Figure 1 shows the horizontal trajectory of the landing approach of the Diamond aircraft that was recorded between 11:38:31 h and 11:55:59 h. During the landing approach, the geodetic latitude coordinate took the values from 53.791864\({}^{\circ}\) to 53.774913\({}^{\circ}\). At the same time, the geodetic longitude coordinate L ranged from 20.408362\({}^{\circ}\) to 20.460093\({}^{\circ}\). The values of the horizontal coordinates (B, L) were determined with use of Equation (1). \begin{table}
\begin{tabular}{c c} \hline
**GPS Time [h:mm:ss]** & **Value [TECU]** \\ \hline
07:00:00 & 9.2 \\
08:00:00 & 12.6 \\
09:00:00 & 16.1 \\
10:00:00 & 19.1 \\
11:00:00 & 21.3 \\
12:00:00 & 22.6 \\ \hline \end{tabular}
\end{table} 
Table 1: The VTEC values for the analysed time period [70]. Figure 1: The horizontal trajectory at approach of landing procedure. The next illustration-Figure 2 shows the characteristics of the vertical trajectory of the flight during the aircraft landing procedure, in the period from 11:38:31 h (41,911 s) to 11:55:59 h (42,959 s) according to system time GPST. The ellipsoidal height h during the approach to landing changed from 515 m to 163 m. The values of the vertical coordinate h were determined with use of Equation (1). Then, Figure 3 shows the number of GPS satellites for which corrections were developed respectively from SDCM and EGNOS geostationary satellites. During the landing approach procedure, the Sepentrio on-board receiver recorded from 6 to 9 GPS satellites with EGNOS corrections, as well as 5 to 8 GPS satellites with SDCM corrections. Additionally, the mean number of tracked GPS satellites with SDCM corrections during the landing approach was 6, while the number of GPS satellites with EGNOS corrections was 7. The analysis of the results presented in Figure 3 reveals that the EGNOS system sent corrections to a larger number of GPS satellites than the SDCM system. The conducted flight test also involved the determination of the dilution of precision coefficient in 3D space-the geometric PDOP (Position DOP) coefficient. The PDOP is a coefficient that is used in GNSS systems to define the influence of the spatial location of GNSS satellite on the accuracy of the determined three-dimensional position [71]. In the present study, the PDOP was determined for an individual SBAS solution, i.e., for the EGNOS and SDCM systems. Figure 4 shows the values of the PDOP coefficient from an individual SBAS solution, i.e., EGNOS and SDCM during the phase of approach to landing of an aerial vehicle. The value of the PDOP coefficient for a single SBAS/EGNOS solution ranged from 1.8 to 2.8, with a mean value of 2.2. For a single SBAS/SDCM solution, the value of this coefficient ranged from 2 to 3.6, while the mean value was also 2.2. The values of the PDOP coefficient obtained for both single SBAS/EGNOS and SBAS/EGNOS did not exceed 3, which means that the observation conditions during the test flight were very good. Figure 2: The vertical trajectory at approach of landing procedure. The second stage of research consisted in the pre-processing of the recorded GNSS satellite data. During the test flight, the on-board receiver Septentrio AsterRx2i was used to collect and record the GPS observations to calculate the position of the aircraft.