The principal limiting error in modern space geodesy techniques is the mis-modeling of the atmospheric delay. This delay, usually separated and referred as hydrostatic (dry) and wet, is described as the product of its value at the zenith and a function that scales its elevation dependence. Accordingly there are proposed models for the prediction of the zenith delay as well as for scaling this zenith value at other elevations. Most of the available dry zenith delay models are global ones. Such models do not satisfy the requirements of precise geodetic application for Egypt, so a new model is very needed for the Egyptian local meteorological conditions.
Current paper introduces a local dry zenith model using surface meteorological data. The new model is based on empirical least squares fitting of the expected delays as calculated using ray tracing. Meteorological data from nine locations evenly distributed over Egypt were used for this model. The results indicated that the zenith dry delay values could be calculated accurately using surface pressure. To test the designed model, additional two sites were used. The tests of the new model showed that it is accurate to about 1.0 mm and its performance meets the needed accuracy for the present precise geodetic application such as crustal deformation studies in Egypt.
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