文档介绍：EM 1110-2-1003
1 Jan 02
Chapter 7
Positioning Techniques for Offshore Engineering Surveys
7-1. General Scope and Applications
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 essible 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 hydrographic survey system, or (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. The following topics are covered under this chapter:
Section I: Sextant Resection Positioning
Section II: Triangulation/Intersection Positioning
Section III: