Assessment of precise GPS ephemeris and clock in the International GNSS service

Currently many vessels determine an overhead clearance by a rule of thumb based on their draft for maritime navigation. Therefore when vessels navigate, they don't have a good overhead clearance because vertical position of vessels varies on time by tidal. As a result, it is occurred maritime accidents that the mainmast of vessels is bumped against overhead facilities. This paper evaluates precise GPS satellite ephemerides and clocks provided by the IGS for applying to maritime precise positioning. And this paper shows that it is necessary to have shorter interval IGS products in real-time for more precise positioning solution.