الفهرس Only 14 pages are availabe for public view
 |  | from | 160 |  |  |
| | | from | 160 | | |
Abstract
The positioning accuracy using the GPS system depends, among other criteria, on th satellites constellation, i.e. the position and number of visible satellites in the sky durin the observation session. To describe this parameter a new term has been defined, Oilutio OfPreeision or simply OOP. The OOP value describes the effect of the satellites positions . on the accuracy of the positioning process.
:,Knowledge of the value of dilution of precision is very important during observation :llCSSions, because many projects have special requirements regarding the positioning eccuracy. These special requirements will force the surveyor to hold the survey mission . . the value of dilution of precision at the time of observation meets the project’s ~uirements. This will result in longer observation sessions and subsequently higher cost for the overall survey process.
For this reason this thesis was dedicated to study the dilution of precision and number of visible satellites values and variations with time and space using several analyses, such as, studying the values and variations of the OOP’s values over a single station, several stations forming a grid covering Egypt and several stations forming a grid covering the whole world. Also the prediction methodology of the dilution of precision and number of visible satellites which can be simply referred to as ”The GPS Mission Planning” was introduced along with a comparison study between the available satellite ephemerides and its performance in the process of GPS mission planning. The satellites ephemerides were downJoaded from several internet based GPS service agencies.
It was found that, under the current satellite constellation the POOP, for single station, can be considered excellent for almost 95% of the analysis period using mask angle of 10° and neglecting the effects of the field obstacles. The maximum POOP mean value during the analysis period for Egypt and the whole world was 2 and 2.3, respectively. Ouring the analysis of the available satellite ephemerides it was found that, the use of broadcast ephemerides instead of the almanac data during six days after the broadcast ephemerides . validation period expires will improve the OOP prediction accuracy and the satellites coordinates prediction accuracy by nearly 30% and 41 %, respectively.
Moreover, a new GPS mission planning software was developed during this study. This software’s integrity was checked and proven to be accurate and dependable in the course of GPS mission planning. The software is expected to facilitate the study of the dilution of precision for the GPS researchers. Also it can give a great deal of help to the GPS users.