Practical GPS field operation

Abstract

The space based Global Positioning System (GPS) was originally developed for navigation purposes. Before this system was introduced, classical astronomical methods using observations to the sun or stars, or radio navigation systems, such as Loran and Decca were utilized for several decades. Later, the Navy Navigation Satellite System (NNSS) was introduced and widely utilized, not only for navigation but also for surveying purposes. However, these old systems had many drawbacks. The astronomical methods require a precise clock and depend on the weather conditions. The terrestrial radio systems do not suffer from these drawbacks, but their area of operation is rather limited. The NNSS, though globally applicable and with better accuracy than most of the other systems, requires a long observation time. For navigation purposes, the new GPS system cleared almost all defects of the old systems, covering the entire surface of the Earth with signals from at least four satellites at any time. For real time absolute positioning applications its accuracy in general is satisfactory. However, due to the structure of the signals used for navigation, which consist of codes modulated on two carriers, the accuracy for high precision surveying applications is not good enough.