Visibility and Geometry of Global Satellite Navigation Systems Constellations

Nowadays (November 2015) there are two global fully operational satellite navigation systems, American GPS and Russian GLONASS. Two next are under construction, Galileo in Europe and BeiDou in China. As the error of observer’s position obtained from these systems depends on geometry factor DOP (Dilution Of Precision) among other things the knowledge of the number of satellites visible by this observer above given masking elevation angle H_min and the distributions of DOP coefficient values, GDOP in particular, is very important. The lowest and the greatest number of satellites visible in open area by the observer at different latitudes for different H_min, the percentage of satellites visible above angle H (9 intervals, each 10^O wide), distributions (in per cent) of satellites azimuths (8 intervals, each 45^O wide) and GDOP coefficient values (8 intervals) for H_min = 5^O for all these four systems at different observer’s latitudes (9 intervals, each wide 10^O wide) are presented in the paper. Additionally the lowest elevation for which the number of satellites visible at different latitudes by the observer in open area above this angle is equal 4 or 3 and the distributions (in per cent) of GDOP coefficient values for different Hmin at observer’s latitudes 50-60^O for the same four systems are showed. All calculations were made for constellation of GPS 27 satellites, GLONASS 24, Galileo 30 and BeiDou 27 MEO satellites.