Global Positioning System (GPS)

Ephemeris data is data that tells the GPS receiver where each GPS satellite should be at any time throughout the day. It describes the path that the satellite is following as it orbits the earth. In other word, it is a set of parameters that used to calculate the location of a GPS satellite at a particular point in time accurately.

Each satellite will broadcast its own ephemeris data showing the orbital information for that particular satellite only. Ephemeris data is very precise orbital and clock correction data necessary for precise positioning, therefore it is usable for a limited time (a few hours or less, depending on the manufacture). Up-to-date data is needed to minimize error that results from minor variations in a satellite’s orbit.