Chapter 1: Precision Survey Properties and Techniques Chapter 1: High-Precision Survey Properties Chapter 1: Precision Survey Properties and Techniques By John Ogundare, Ph.D.

Chapter Objectives Be able to perform the following: Explain the main properties of precision survey procedure with respect to basic survey procedure Discuss the properties of the main classes of precision surveys Explain different traditional measurement techniques used in precision surveys Discuss the uses of different computation models for precision surveys Discuss the technology progress in geodetic surveying equipment Evaluate some safety issues to precision survey projects

Properties of Precision Surveys Precision surveying - application of appropriate field of surveying to a project to achieve a desired accuracy (or precision) Significant properties: Precise and expensive instrumentations are used – typical tolerance or accuracy is up to 0.1 mm or better Stricter observations and data handling methods (increased time, effort & costs) are required Larger number of observations are collected – redundancy is important in assessing accuracy and reliability of results More rigorous mathematical treatment for error evaluation is required

Qualification of Precision Surveyor Understand intended use of survey measurements Sources of errors in measurements – error budgeting Design of survey scheme – appropriate instrumentation Field survey procedures to minimize errors Rigorous adjustment & analysis of measurements

Classes of Precision Surveys Geodetic control network surveys Monitoring and deformation surveys Geodetic engineering surveys Industrial metrology Surveys for research and education (scientific applications such as in geodynamics)

Geodetic Control Network Surveys Surveys which consider the true shape and size of the earth (e.g., ellipsoidal model, not a plane model) – conducted over large area Establishes horizontal and vertical control points (absolute positions known) to support: Basic framework (e.g., CSRS, NSRS, ESRS) for a country – useful as reference for topographic mapping, boundary demarcation, mapping natural resources, etc. Engineering and construction projects (bridges, dams, tunnels, highways, pipelines, etc.) Reference for positioning marine construction vessels (dredging) Reference for monitoring and evaluating deformations of large extent (tectonic plate, land slide, etc.)

Geodetic Control Network Surveys: Models Computation model: True shape of the earth (e.g. ellipsoid) is considered Absolute three-, two- or one-dimensional positions of points are determined

Monitoring and Deformation Surveys Essential for understanding natural phenomena (earthquakes, land slides, crustal movement) and behavior of man-made structures (dams, bridges, tunnels, building, etc.) Compared with geodetic control surveys: Computation model: Absolute position not of interest but relative is; three-, two-, one-dimensional relative positions of points are needed Measurements between epochs must be made in similar atmospheric conditions and instruments used must be similar

Geodetic Engineering Surveys Application of rigorous geodetic methods to control and support engineering projects: Construction and maintenance of tunnels, bridges, hydroelectric power stations Relative positional accuracies of 10 ppm or better required Most first order national geodetic networks may be unsuitable because of distortions in national frame Local coordinate system (unlike the national frame) is commonly used

Geodetic Engineering Surveys: Branches Mining surveying – about rock stability control & protection Land surveying – focusing on establishing boundary lines of real property ownerships Computation model: Local coordinate system and relative positioning Plane earth surface model (plane local coordinate system requiring map projection) is used for computation Unacceptable distortion is extended too much beyond the coordinate origin

Progress in Equipment: (TMPL) Project Choosing appropriate route: from use of topo maps, GIS, Google Earth to LIDAR systems Acquiring right-of-way: from use of theodolite & chains to total station equipment and GPS Leveling to desired grades: differential leveling procedure still common, but faster instruments like digital levels compared with optical levels

Industrial Metrology (or Survey) Uses precision measuring techniques for positioning and aligning industrial machinery and scientific apparatus, including: Aligning components of large antennas (parabolic, flat, etc.) Checking aircraft dimensional quality of the various sub-assemblies Mapping submarine hull Alignment of magnets of colliders and alignment of accelerator facilities Setting up and aligning machines in the industries In-situ calibration of industrial robots

Industrial Metrology: Model Geodetic metrology: uses geodetic measuring techniques Computation model: three-dimensional local coordinate system Optical tooling (or optical alignment): extremely accurate measurements are made using jig transits, optical squares, aligning telescopes, optical micrometers, laser interferometry Computation model: along lines or planes

Precision Geodetic Survey Techniques Techniques require: Using precision equipment (stretching performance to limit of accuracy) – Theodolites, EDMs, total stations, Levels, GNSS surveys Using GNSS (such as GPS, GLONASS, Galileo, etc.): Generally used for most horizontal control surveys and precise surveys Conventional surveys used in local and isolated monitoring schemes Selection of right GNSS receiver for a particular project is critical to success of a project Receiver selection depends on: Applications Accuracy requirements Signal processing requirement

GNSS Surveys: Receiver Quality GNSS geodetic quality receivers used in precision surveys: They can process both code and carrier phases Carrier phase receivers can be single frequency of dual frequency; dual frequency types are recommended When receivers are used with a remote one (in static differential mode), the receivers shall have accuracy of 5 mm or better on baselines less than 1 km Processing software must be able to process broadcast and precise ephemerides. A minimum of 2 receivers needed for a project; same antenna type for all receivers to minimize phase centre biases

Conventional Horizontal Positioning Techniques Techniques include: Triangulation, trilateration, combined triangulation and trilateration, traversing, intersection and differential leveling Combined triangulation and trilateration survey techniques produce the strongest network of horizontal control –recommended for high-precision surveys Tunnel surveys in mountainous areas will require combined triangulation and traverse surveys Triangles of a triangulation or a trilateration network should contain angles greater than 15 - 25 Underground surveys are based on open traverses measured with theodolite, total station, EDM and gyroscopic instrument (e.g., GYROMAT 2000) to provide orientation Intersection method is commonly used in 3D coordinating systems Resection: used to determine position and height of instrument setup station when measurements are made to at least two known points- in free-stationing to minimize the effect of centering error on angles

Geodetic Vertical Positioning Techniques Techniques include establishing elevations of points with reference to the geoid: Providing vertical control points Differential leveling as the precise leveling technique (for first- or special-order accuracy) Standard deviation of less than 1 mm/km or better may be desired – using precision spirit levels with micrometer or digital levels and invar rods

Review of Some Safety Issues Needed as part of every survey project Crews are to conform to some design safety rules to allow them to perform their duties in a safe manner Dedicated personnel should be assigned sole responsibility of managing and promoting safety of work crews: Taking appropriate actions on safety issues Creating safety awareness Organizing regular safety meetings Safety issues: recognizing hazards, taking precautions, operating equipment safely, first aid procedures, understanding safety precautions.