# Designation of the Quality of EGNOS+SDCM Satellite Positioning in the Approach to Landing Procedure
## 3 Research Experiment  
In reference to the analysis of the state of knowledge concerning the application of SBAS supporting systems in aviation, this study focused on the final stage of flight being the landing approach and landing. To this end, first a flight experiment was conducted, followed by the elaboration of the GNSS data, and finally, the necessary numerical analyses were conducted for the research methodology proposed in the paper. The first stage consisted of performing a test flight. The flight was conducted jointly by a research team composed of employees of the Polish Air Force University, the University of Warmia and Mazury, and the Aero Club of Warmia-Mazury. The test flight was performed with a Diamond DA 20-C 31 aircraft on 31 October 2020, in north-eastern Poland. A dual-frequency geodetic receiver Sepentrio AsterRx2i was installed on board of the aircraft. The flight lasted from 07:57:07 h (28,627 s) to 11:55:59 h (42,959 s) according to GPS Time (GPST). The Sepentrio receiver recorded GPS satellite data at 1-s intervals. The obtained data were used to calculate the position of the aerial vehicle and the quality parameters of satellite positioning based on Equations (1)-(9). During the entire flight, the scope of changes in the geodetic latitude B ranged from 53.458121\({}^{\circ}\) to 54.097633\({}^{\circ}\), while the scope of geodetic longitude L was in the range from 20.363363\({}^{\circ}\) to 22.982004\({}^{\circ}\). The ellipsoidal height during the flight ranged from 139 m to 605 m. Additionally, the momentary velocity of the flight of the Diamond aircraft along the B axis ranged from 0 to 58 m/s, for the L component from 0 to 96 m/s, and along the h axis from 0 to 9 m/s. An important element of the description of the flight experiment was the information about atmospheric conditions, i.e., respectively, the tropospheric and ionospheric conditions. The analysis of meteorological conditions was based on the data obtained from the weather station located in Olsztyn [65]. On the 31 October 2020, the air temperature in north-eastern Poland fluctuated between 6 \({}^{\circ}\)C and 10 \({}^{\circ}\)C, and the mean temperature was 8 \({}^{\circ}\)C. The highest temperature was noted at 11:30. There were heavy clouds, but the largest cloud coverage was noted after the end of the experiment, i.e., after 12. The wind was weak and moderate, from the western and north-western directions. No fog was observed during the flight. Air humidity ranged from 76% to 100%, with the mean value of 90%. As it was in the case of cloud cover, the lowest value of air humidity was noted during the realisation of the test flight. The atmospheric pressure in north-eastern Poland was initially 1017 hPa, and it increased in the subsequent hours. The highest value of air pressure, i.e., 1024 hPa, was recorded at 12:00 h.  
As for the state of the ionosphere, the value of the Kp index for the 31 October 2020 was presented. The Kp index is a parameter that defines the radiation of solar wind particlesthat affect the magnetic field of the Earth [66]. Its value allows us to find out whether geomagnetic storms that might cause disturbances in the GNSS signal occurred during the experiment. During the flight of the Diamond, from 07:57:07 h (28,627 s) to 11:55:59 h (42,959 s) according to GPS Time (GPST) two values of the Kp index were determined: 2.34 at 7:50 h and 2.00 at 10:50 h. Thus, it may be stated that the values of the Kp index during the realisation of the experiment were low. Data related to the Kp index were downloaded from the website [[https://www.swpc.noaa.gov/products/planetary-k-index](https://www.swpc.noaa.gov/products/planetary-k-index)]([https://www.swpc.noaa.gov/products/planetary-k-index](https://www.swpc.noaa.gov/products/planetary-k-index)) (accessed on 30 November 2021) [67]. With regard to the status of the ionosphere, the values of the VTEC (Vertical TEC) parameter [18; 68; 69] were also determined during the flight.