Assessment of tropospheric delay models in GPS baseline data analysis

In the recent years, GPS has become the most commonly used survey instrument. It is used to get high precise coordinates. In order to achieve that, we must remove or reduce the effect of troposphere error. Several models can treat the troposphere error under dry and normal (wet and dry) atmosphere conditions. On the other hand, the troposphere error can be ignored. These models were not evaluated for the Egyptian local climate conditions using real GPS data. An assessment of these models is needed to choose the most suitable one.Around the northern part of the Nasser Lake, the GPS measurements were initiated in 1997. A GPS network consisting of 11 sites has been established by the National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt, to investigate the crustal deformation in this important region. The GPS observations of this network were carried out using dual frequency Trimble 4000SSI receivers. Data used in the study are 7 baselines that connect with 9 stations out of this GPS network. Definitely, one day of the 2004 GPS data is processed; day 105 (April 14th) from about 6 am to 12 pm with 0º mask elevation angle and interval sampling rate of 30 seconds.The data of medium lengths regional network at Aswan were processed by using Bernese software (version 5.0). Dry Niell model was used as a model of troposphere with elevation angle equal to 0o and a site-specific troposphere parameter was considered with wet Niell as a model of mapping function and horizontal gradient estimate model is Tilting. This solution is considered as the reference solution of network. Then 7 baselines were selected and processed considering all possible cases of baseline location and bearing. The results of each baseline solution were compared with the multipoint (reference) solution.