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When we use GPS for positioning, we are affected by a variety of factors. The factors that affect the accuracy of GPS positioning can be divided into the following four categories:
1. Factors related to GPS satellites
1.SA Policy
Proceeding from its national interests, the United States has artificially reduced the accuracy of ordinary users using GPS for navigation and positioning by reducing the accuracy of broadcasting ephemeris (technology) and adding high-frequency jitter (technology) to the GPS reference signal.
2.Satellite ephemeris error
In GPS positioning, the orbital parameters of the satellite required to calculate the position of the GPS satellite at a certain time are provided through various types of ephemeris, but regardless of the type of ephemeris, the calculated satellite position will be different from its real position, which is called ephemeris error.
3.Satellite clock difference
Satellite clock aberration is the error between the clock face time of an atomic clock installed on a GPS satellite and the GPS standard time.
4.Deviation of the phase center of the transmitting antenna of the satellite signal
The phase center deviation of the satellite transmitting antenna is the difference between the nominal phase center of the transmitter antenna and its true phase center on a GPS satellite.
2. Factors related to the route of transmission
1.Ionospheric delay
Due to the refractive effect of the ionosphere around the Earth on electromagnetic waves, the propagation speed of the GPS signal changes, and this change is called ionospheric delay. The influence of ionospheric refraction on electromagnetic waves is related to the frequency of electromagnetic waves and the total electron content on the electromagnetic wave propagation pathway.
2.Tropospheric delay
Due to the refractive effect of the troposphere on electromagnetic waves around the Earth, the propagation speed of GPS signals changes, and this change is called tropospheric delay. The effects of tropospheric refraction on electromagnetic waves are related to temperature, humidity and air pressure in the electromagnetic wave propagation path.
3.Multipath effects
Due to the influence of the surrounding environment of the receiver, the satellite signal received by the receiver also contains the influence of various reflected and refracted signals, which is the so-called multipath effect.
3. Factors related to the receiver
1.Receiver clock difference
Receiver clock difference is the difference between the clock face time of the clock used by the GPS receiver and the GPS standard time.
2.Receiver antenna phase center deviation
The receiver antenna phase center deviation is the difference between the nominal phase center of the GPS receiver antenna and its true phase center.
3.Errors caused by receiver software and hardware
When performing GPS positioning, the positioning results are also affected by factors such as processing and control software and hardware.
4. Miscellaneous
1.GPS controls some human or computer influences.
Due to problems in the GPS control part or errors introduced by the user when performing data processing, etc.
2.Impact of data processing software
The influence of the imperfect algorithm of the data processing software on the positioning results.