الفهرس 
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Abstract
This research introduce the Global Positioning System errors, The GPS played an important and a pivotal role in every part of modem life and revolutionized in the positioning and navigation systems.
The objective of the proposed research to update the mathematical model used by
Global Positioning System this helps to eliminate the atmospheric errors effect on
the received signals. The proposed solutions are used to overcome the effect of the atmospheric errors by using modeling. The evaluation performances of the ionospheric models are presented from the side of residual ionospheric errors.
The evaluation performances of tropospheric mitigation models are presented from the side of the elevation angle. There are error sources that effect on accuracy of
estimating position when using Global Positioning System. The most important
error sources are (clock drifts, mismodeling of gravitational and non-gravitational forces in different orbits, geometry of the satellites, multi path error, antenna phase
variations, noise generated with the receiver itself and ionospheric and tropospheric atmospheric delays), to get high accuracy in Global Navigation Satellite System (GNSS) these errors must be eliminated.