Natural atmospheric delay is one of the major sources of GPS errors that hinder using it in precise geodetic application. Global dry tropospheric models are derived using available Radiosonde data obtained from Europe and North America continents. The global atmosphere conditions used as constants in these models provide a broad approximation of the tropospheric conditions. Unfortunately, these models did not meet the local meteorological conditions of Egypt. In other words, they do not take into account the latitudinal and seasonal variations in the atmosphere. Besides, daily variation in temperature, pressure and relative humidity can lead to error in tropospheric delays obtained using the global tropospheric models especially in the height components. Hence, these models do not truly reflect the actual tropospheric effect.
With increasing the demands of utilizing GPS in precise geodetic applications, it was inevitably to have a local model to compute the zenith dry tropospheric delay. The current study submits a new local developed model to compute the dry zenith tropospheric delay. The new model is derived from ray tracing of meteorological data at 17 sites covering all Egyptian territory. The new developed model is a linear relationship with the measured surface pressure and temperature data. The tested data at the five locations shows a very good performance. The results confirm how the new local developed model can enhance the use of GPS in precise geodetic applications