Positioning Techniques for Offshore Engineering Surveys

Course Summary

This chapter covers general procedural guidance and quality control criteria for visual, mechanical, electronic, and satellite positioning methods used to control surveys of river and harbor projects. Both terrestrial and satellite positioning systems are covered in this chapter. Terrestrial positioning methods include traditional land-based techniques such as sextant resection, triangulation, tag lines, microwave electronic distance measurement (EDM) systems, and electronic total stations. Since the early 1990’s most of these terrestrial positioning methods have been largely replaced by satellite-based positioning methods, namely GPS and more accurate code phase Differential GPS (DGPS) and Real Time Kinematic (RTK) carrier phase DGPS. Since there are still isolated project areas where satellite GPS methods may be inaccessible or impractical, one of the traditional terrestrial survey methods covered in this chapter may be needed to provide survey control. Examples of such cases may include:

1. Small dredging or marine construction projects where only a limited amount of depth coverage is required.
2. Areas under bridges, in deep-draft harbor berths, or near dams where GPS satellite view is blocked.
3. Intermittent, low-budget projects where traditional positioning methods may prove more economical than equipping a fully automated DGPS based hydro-graphic survey system.
4. Rough reconnaissance surveys where meeting a specific positional accuracy standard is not required.

Procedural methods and quality control (QC) criteria for some of these older survey techniques are retained in this manual primarily for reference purposes.

Learning Objectives

• Sextant Resection Positioning
• Triangulation/Intersection Positioning
• Visual Positioning Methods
• Tag Line Positioning Methods
• Range-Azimuth Positioning Methods
• Land-Based Electronic Positioning Systems
• Global Positioning System Techniques
• Summary of Positioning System Quality Control Standards

Course Author

Department of Army

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This online PDH course can also be used as a continuing education course for the following.

Land Surveyors