The ionosphere is one of several layers of the Earth’s atmosphere. The influence of the ionosphere on
GPS positioning is one of the largest error sources. It is generally modeled in a global scale by determining its
Total Electron Content (TEC) in the signal path using all available world wide GPS observations to be used in
GPS processing procedure to overcome its error, the modeled product is known as Global Ionospheric Model
(GIM). In this research, a Local Ionosphere Model (LIM) was created using Bernese software, by the computation
of TEC in a local area. This process was based on the single layer model to determine the appropriate TEC
values by using the Egyptian coastal part composed of five stations of the network made by the Egyptian National
Research Institute of Astronomy and Geophysics (ENRIAG) at (2001). The influence of using the global
ionospheric model versus the obtained local model was investigated, with precise ephemeris, for different base
line lengths, and different observational sessions (1, 2, 3, 4, 5 and 6 hours), based on the commercial software
Trimble Total Control (TTC). Additionally, the influence of the Precise Ephemeris (PE) alone without using
ionospheric models was also studied for the same base line lengths, and the same observation sessions based
on the same commercial software. The results indicate that the mean of vector length errors was improved when
using the (LIM) with precise ephemeris, at all different baseline lengths and also with different observational
sessions.