GPS positioning and satellite related errors

GPS positioning and satellite related errors

(1) Satellite ephemeris error

The satellite ephemeris error refers to the deviation between the satellite space position given by the satellite ephemeris and the actual position of the satellite. Since the satellite space position is calculated by the ground monitoring system based on the satellite orbit result, it is also called the satellite orbit error. It is a starting data error, the size of which depends on the number and spatial distribution of satellite tracking stations, the number and accuracy of observations, the orbital model used in orbit calculations, and the degree of perfection of orbital software. Ephemeris error is an important source of error in GPS measurements.

(2) Satellite clock difference

The satellite clock difference is the difference between the GPS satellite clock and the GPS standard time. In order to ensure the accuracy of the clock, GPS satellites use high-precision atomic clocks, but the deviation and drift and drift between them and the GPS standard are still within 1ms~0.1ms, and the equivalent error will reach 300km~30km. . This is a systematic error that must be added to the correction.

(3) SA interference error

The SA error is a policy adopted by the US military to limit the accuracy of the system used by the unlicensed user to use GPS for high-precision point location. The SA policy includes the ε technique for reducing the accuracy of the broadcast ephemeris and attaching a random number to the satellite fundamental frequency. The delta technique of jitter. After the implementation of SA technology, SA error has become the most important factor affecting GPS positioning error. Although the United States cancelled the SA on May 1, 2000, the United States may resume or adopt similar interference techniques during wartime or when necessary.

(4) Influence of relativistic effects

This is due to the relative error between the satellite clock and the receiver clock caused by the difference between the state of the satellite clock and the receiver (moving speed and gravitational potential).