Since we are back in lockdown and it's snowing outside, I spent a bit of time trying to track down some academic evidence to address
gpsrchive's challenge, beginning with the "use at high latitudes" question.
For GNSS, performance in high latitude regions is reduced compared to the performance obtained by users at mid-latitudes. The reasons are mainly the satellite-receiver geometry and the ionospheric effects on the satellite signals. The four GNSS constellations have satellite orbits with different inclination angles to the astronomical equator and are at different altitudes above the earth. These two factors account for additional benefits for GLONASS and GALILEO for users at high latitudes such as areas in the North of Canada, Alaska, Northern Europe, and Russia as well as Antarctica compared to GPS alone. Users are likely to see improvements in positional accuracy using multi-GNSS location compared to single constellations at high latitudes.
NB The following academic papers are consistent in their commentary on the use of GNSS at high latitudes. These selected extracts are a relatively small sample of the literature and this does not therefor purport to be an exhaustive or systematic review.
PennState College of Earth and Mineral Sciences, Department of Geography
On-line Course GEOG 862: GPS and GNSS for Geospatial Professionals: Lesson 10.
Link:
https://www.e-education.psu.edu/geog862/home.html
GPS
• 55 degree inclination angle
• altitude 20,200 km
Galileo
• 56 degree inclination angle
• altitude 23,616 km
GLONASS
• 64.8 degree inclination angle
• altitude 19,100 km
BeiDou
• 55 degree inclination angle
• altitudes 38,300, 21,200 km
Cherniak I and Zakharenkova I
New advantages of the combined GPS and GLONASS observations for high-latitude ionospheric irregularities monitoring: case study of June 2015 geomagnetic storm. Earth Planets Space 2017,
69, 66.
https://doi.org/10.1186/s40623-017-0652-0
A significant advantage of the GLONASS, as compared to the GPS, is that the GLONASS has an orbit inclination of ~65°, that is ten degree higher than the GPS orbit inclination. This feature is important for the high-latitude region, where a multi-system GNSS receiver can track the GLONASS navigation signals for much longer time and with higher elevation angles than GPS ones.
Kees de Jong, Matthew Goode, Xianglin Liu, and Mark Stone.
Precise GNSS Positioning in Arctic Regions. This paper was prepared for presentation at the Arctic Technology Conference held in Houston, Texas, USA, 10-12 February 2014.
https://www.researchgate.net/publicatio ... ic_Regions
As the name implies, Global Navigation Satellite Systems (GNSS), such as the US GPS and Russian GLONASS, provide worldwide coverage for position determination. However, especially in arctic regions, there are a number of issues to be resolved or taken into account. The most important ones are:
- Satellite geometry may not be as good as at lower latitudes, due to the satellite orbits. For example, for GPS the orbits have an inclination with respect to the equator of 55 degrees. As a result, satellites can be seen at 90 degrees elevation only for latitudes equal to or below this inclination. For arctic latitudes, the maximum elevation is much lower, leaving a hole in the sky above these regions in which no satellites are visible. In particular the height component determined from GPS is worse than at lower latitudes.
- Ionospheric effects are more severe than at mid-latitudes (but in general not as severe as in equatorial regions). Part
of the problem can be solved by using multi (dual or triple) frequency GNSS receivers, another part by using more
systems: not only GPS, but a combination of e.g. GPS and Glonass and in the future the European Galileo and
Chinese BeiDou as well.
An image comparing 24 hour plots of GPS satellites visible from Copenhagen in Denmark to Longyearbyen in Svalbard can be viewed here:
https://mycoordinates.org/challenges-fo ... he-arctic/
Horizontal position accuracy is in many cases reduced because there is a higher noise level in the observations, caused by the large number of more noisy low elevation satellite signals. The low elevation of the satellites further worsens the ionospheric effect on satellite signals.
Eissfeller, B, Ameres, G, Kropp, V, Sanroma, D.
Performance of GPS, GLONASS and Galileo, University of Stuttgart, 2001.
https://phowo.ifp.uni-stuttgart.de/publ ... feller.pdf
Users in higher latitude areas, such as Canada, obtain better GLONASS derived dilution of precision (DOP) than users of GPS. This is due to the high inclination angle of GLONASS: 64.8 degrees compared to 55 degrees for GPS.
Stelian Cojocaru, Eugen Barsan, Ghiorghe Batrinca and Paulica Arsenie
GPS-GLONASS-GALILEO: A Dynamical Comparison.
Maritime Transport & Navigation Journal, 2009;
1(1): 1-13
https://www.researchgate.net/publicatio ... comparison
A constellation of 30 satellites, 27 active and 3 spare, will populate the spatial segment of GALILEO Satellite System. The satellites will be deployed in 3 circular orbits with radii equal to around 29,600 km, inclined with 56° on the equatorial reference plane. Having ten satellites quasi-equally distributed in each of the three circular orbits, flying at an altitude of around 23,222 km with an orbital period of 14 sidereal hours, the constellation will ensure a global coverage of the Earth. As soon as Full Operational Capability is achieved, the designed space segment will provide 6 to 8 visible Galileo satellites from any terrestrial (or near-terrestrial) location. The combination of the orbital inclination and the flight altitude of the satellites will considerably increase the coverage of the polar regions, not so well achieved by GPS.