Atmospheric water vapour degrades the accuracy of the results of space geodetic observations due to permanent electric dipole moments. It creates excess path lengths by retarding (slowing and bending) the propagation of the electromagnetic waves that are used in global positioning system (GPS) and very long baseline interferometry (VLBI) observations. It is known that the excess path lengths are less than 30～40 cm at the most, and are the primary obstacles of space geodesy because of the highly variable distribution of water vapour in the atmosphere. In this study, we compared modern five wet mapping functions by evaluating their effects on the tropospheric signal delay and position estimates in GPS data processing, and precise Egypt wet mapping function model is derived based on eight stations of radiosonde data welldistributed over and around Egypt (five stations used to estimate new model and other three as check points). To derive the new Egypt wet mapping function, the troposphere is divided into regular small layers. Ray tracing technique of actual signal path traveled in the troposphere is used to estimate tropospheric slant delay. Real GPS data of five stations (RTK-Network methods) were used for the assessment of new model against the available international models. These international models include Niell (NMF), Black & Eisner (B&EMF), Ifidas (IFMF), Hearing (HMF), and UNBabc MF. The data were processed using Bernese software version 5.0. The results indicate that the new Egypt wet MF model is the best model at Egypt region and has improved the wet tropospheric delay estimation up to 23.3 percent at five degree elevation angles.
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