Spiney wrote: ↑Mon Jan 11, 2021 11:33 pm
This recent article entitled "Comparative Study on GNSS Positioning Systems for Autonomous Vessels in the Arctic Region" should be of interest to your research:
http://ceur-ws.org/Vol-2626/paper12.pdf
That is an interesting GNSS simulation study.
I have also been researching GNSS availability using various satellite prediction services. I wanted to know which GPS, GLONASS and Galileo satellites would be visible, where in the sky they would be located, and the path they would be following relative to multiple latitudes in the northern hemisphere. I recorded results for latitudes of N 5°, N 25°, N 45°, N 65°, and N 85°, all at a longitude of E 25°. The results can be seen in the charts below.
While the number of visible satellites for each constellation fluctuated slightly from one hour to the next, the total number of available satellites at each latitude did not vary significantly. This did not surprise me as all constellations tested provide global coverage.
Over the 24 hour period tested (one full rotation of the Earth), GPS always provided the most visible satellites, while GLONASS and Galileo both maintained similar visibility levels, usually within one or two satellites of each other. Never were there an insufficient number of satellites available. Choosing GPS + GLONASS
or GPS + Galileo always yielded a similar number of available satellites.
The charts also revealed how the position of those satellites in the sky changed at each latitude. As the latitude increased, fewer satellites were available directly overhead. Not the total number of available satellites, mind you. Just the number of satellites located directly overhead.
I do not see how this creates any issues, as satellites located at higher elevations in the sky are best suited only for GPS elevation calculations. Conversely, satellites located at lower elevations in the sky (nearest the horizon) are considered least suitable for any position calculations, while those located midway in the sky are best suited for calculating latitude and longitude coordinates. This is where the majority of the satellites appeared in each chart.
E 25° N 5°
GNSS View LAT 05.png
E 25° N 25°
GNSS View LAT 25.png
E 25° N 45°
GNSS View LAT 45.png
E 25° N 65°
GNSS View LAT 65.png
E 25° N 85°
GNSS View LAT 85.png