Principles and Practice of GPS Surveying

OVERVIEW

The Global Positioning System (GPS) is a space-based, microwave, 24-hour, all-weather, global military navigation system designed, deployed, financed and managed by the U.S. military authorities. Since GPS was declared operational in mid-1993 it has had a profound impact on the art and practice of most forms of positioning and navigation. However, GPS has already had a tremendous impact on surveying, initially as a technology for "control surveys", for which purpose it was first introduced into many countries during the early 1980's -- well before the full satellite constellation was available to navigation users. In fact, the application of GPS for control surveys (or so-called "geodetic" surveys) was the first civilian use of GPS which was well beyond that for which GPS was originally intended by its military designers.

Nowadays GPS surveying techniques have completely replaced technologies such as Doppler satellite positioning and even long-range EDM for traditional first (and lower) order control surveys. However, the adoption of GPS is not restricted to control survey applications. More and more GPS is being used for cadastral, topographical and engineering surveying. The constraints that have previously restricted the application of GPS technologies, primarily those of cost (capital and running) and productivity (measured in terms of the numbers of points which can be coordinated in a day) are being aggressively addressed by the manufacturers, and it is confidently predicted that GPS will shortly be used by the majority of surveyors and geomatic engineers.

These notes are designed to provide the reader with an understanding of the principles and practice of GPS surveying. The subject is divided into twelve topics:

• Topic 1: Principles of satellite positioning
• Topic 2: Introduction to GPS positioning
• Topic 3: The GPS signals
• Topic 4: GPS instrumentation
• Topic 5: GPS satellite surveying
• Topic 6: Modelling GPS observations
• Topic 7: Introduction to GPS processing
• Topic 8: GPS baseline processing
• Topic 9: Elements of GPS network processing
• Topic 10: GPS and quality control
• Topic 11: Result transformation and presentation
• Topic 12: Datums and the future of GPS

An important objective of these notes is to dispel myths and incorrect perceptions of the capabilities (and shortcomings) of the technology. This is generally the result of people being bewildered by the ever increasing GPS "jargon". Hence it is necessary, for example, distinguish between the "GPS navigation" techniques based on the relatively imprecise pseudo-range observations (for which GPS was originally designed, and which is still the standard positioning mode for navigation-type applications), and the "GPS surveying" techniques specifically developed for precise positioning applications (which make use of the phase observations of the signal carrier waves).

In addition to focussing on the specialist technology of "GPS surveying", the sub-categories of "conventional GPS surveying" as well as "modern GPS surveying" will also be covered in these notes. Why is this necessary? Contributing to the increasing popularity of GPS has been the evolution of precise GPS surveying from a relatively difficult, expensive and complicated technology that could only be used in the so-called "static" mode, to a technique that has tremendous flexibility, including being able to be used in the "kinematic" (moving receiver) mode. This increases the number and range of applications that can be addressed by the GPS surveying technology. To therefore appreciate the directions in which GPS is developing, as well as to be aware of the real (and perceived) constraints on GPS performance, it is necessary to understand the fundamental principles of the GPS hardware, processing algorithms and operational procedures. These notes give this background.

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© Chris Rizos, SNAP-UNSW, 1999