Adjustment Computations, 6th Edition

CHAPTER 17ADJUSTMENT OF GNSS NETWORKS

17.1 INTRODUCTION

For the past seven decades, NASA and the US military have been engaged in a space research program to develop a precise positioning and navigation system. The first-generation system, called TRANSIT, used six satellites and was based on the doppler principle. TRANSIT was made available for commercial use in 1967, and shortly thereafter its use in surveying began. The establishment of a worldwide network of control stations was among its earliest and most valuable applications. Point positioning using TRANSIT required very lengthy observing sessions, and its accuracy was at the 1 m level. Thus, in surveying it was suitable only for control work on networks consisting of widely spaced points. It was not satisfactory for everyday surveying applications such as traversing or engineering layout.

Encouraged by the success of TRANSIT, a new research program was developed that ultimately led to the creation of the Navigation Satellite Tracking and Ranging (NAVSTAR) Global Positioning System (GPS). This second-generation positioning and navigation system utilizes a nominal constellation of 24 orbiting satellites. The accuracy of GPS was a substantial improvement over that of the TRANSIT system, and the disadvantage of lengthy observing sessions was also eliminated. Although developed for military applications, civilians, including surveyors, also found uses for the GPS system.

Since its introduction, GPS has been used extensively. ...