الفهرس 
STRUCTURE OF THE EARTH’S ATMOSPHERE
ZENITH DRY DELAY MODELINGOnly 14 pages are availabe for public view
 |  | from | 142 |  |  |
| | | from | 142 | | |
Abstract
Global Positioning System (GPS) has become an important aid in many essential applications such as, point positioning, road construction, earth moving, and marine surveying. GPS measurements are affected by several types of random errors including orbital errors, satellite clock errors, and errors due to signal propagation through the atmosphere. The signal propagation errors include the delay of GPS signal as it passes through the ionosphere and the neutral atmosphere, ionospheric delay and tropospheric delay respectively. Ionospheric delay can be completely removed by using dual frequency observations. Tropospheric delay is often treated using the standard tropospheric models.
Several correction models and mapping functions are currently used to predict the dry tropospheric delay. The purpose of this thesis is to evaluate and compare the performance of these correction models and mapping functions regarding its accuracy to estimate the dry component of the tropospheric delay at different elevation angles. The purpose of this research is extended to develop a new mapping function which has better performance at low elevation angles up to 5° and also is more suitable for the atmospheric conditions of Egypt.
The results revealed that Saastamoinen model is recommended for zenith angles up to 30˚ but for zenith angles more than 30˚ the most precise model is Hopfield model. In addition the Black & Eisner mapping function is recommended for dry tropospheric delay prediction for low zenith angles up to 80˚while for elevation angles up to 10˚ Moffett mapping function will be the reliable choice. It can also be concluded that the new developed mapping function has proved its ability to provide better estimation for the dry tropospheric delay suitable for the atmospheric conditions of Egypt at low elevation angles up to 5°.