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Each gps satellite passes over a DoD monitoring station twice daily. The variations such as altitude, position and speed are carefully checked. Any variations are called "ephemeris" errors. They are usually very small and are caused by gravitational influences of the sun and moon and the pressure of solar radiation on the satellite. Once the DoD has measured a satellite's position the information is relayed back up to the satellite. The satellite will then broadcast these minor corrections along with it's timing information.
Also, the GPS accuracy can purposefully be degraded by DoD using an operational mode called "selective availability" (S/A) which is designed to deny to hostile forces the tactical advantage of gps positioning
so, we know a lot about gps generally, but what do we know about gps that is build within the 3g iphone
Also, the GPS accuracy can purposefully be degraded by DoD using an operational mode called "selective availability" (S/A) which is designed to deny to hostile forces the tactical advantage of gps positioning
so, we know a lot about gps generally, but what do we know about gps that is build within the 3g iphone