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Surveying II
UNIT IV
GPS SURVEYING
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Basic concepts – Different segments
– space control and user segments –
satellite
configurationsignal
structure – orbit determination and
representation – antispoofing – and
selective availability – Task control
segment -Hand held and Geodetic
receivers – data processing –
Traversing – and triangulation
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parts of system include:
space (GPS satellite
vehciles, or SVs)
control (tracking
stations)
users
first one launched in 1978
….June 26, 1993
Air Force launched 24th SV
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Design Objectives of GPS
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Suitable for different platforms: aircraft, ship, land-based and space
(missiles and satellites),
Ability to handle a wide variety of dynamics,
Real-time positioning, velocity and time determination capability to an
appropriate accuracy,
Single global geodetic datum (reference system) for defining position,
Differential accuracy standards: highest accuracy to be restricted to a
certain class of authorized users,
Resistant to jamming (intentional and unintentional),
Redundancy provisions to ensure the survivability of the system,
Passive positioning system that does not require the transmission of
signals from the user to the satellite(s),
Ability to provide the service to an unlimited number of users and
world-wide coverage
Low cost, low power, therefore highly complex satellite segment,
Total replacement of the Transit 1 satellite and other terrestrial
navigation aid systems.
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Introduction
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Signal Measurement Techniques
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Geocentric & geodetic Reference Systems
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Time Systems
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Satellite Configuration
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Principles Of Global Positioning System
(GPS)
What is GPS?
The GPS reference system
The GPS system components
 The space segment
 The control segment
 The user segment
GPS positioning principles
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Space Segment
Constitutes satellite constellation which downlinks data including coded
ranging signals, position information, atmospheric data, and almanac
(data about approximate orbit information of all satellites).
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Basic functions of satellites include:
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Receive and store information transmitted by the control station
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Perform limited data processing by its own computer
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Maintain very accurate time by means of onboard 2 cesium and 2
rubidium oscillators
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Transmit information to the user by the signal message
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Maneuver to position in space controlled by the control segment
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Figure 5.1 GPS constellation consisting of six orbital planes with four
satellites in each plane. Each satellite is identified with a twocharacter code: a letter identifies the orbital plane (A through F)
and a number identifies the satellite number in the plane (Enge and
Misra, 1999)
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Control Segment I
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It consists of 5 tracking station to
collect data based on observing
satellite in their orbits. Tracking is
executed with two frequency
receivers equipped with highly
precise cesium oscillators.
Meteorological data is also collected
for
accurate
evaluation
of
tropospheric delay (explained later
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in Lecture 10).
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Control Segment II
•One MCS, takes data from other 5 tracking
stations and consequently predicts satellites
orbits by extrapolation.
•Computes clock correction for satellite time
referred to GPS time frame.
•Satellite time synchronization is carried out by
connecting MCS to US Naval Observatory
(USNO) in Washington DC.
The clock correction data is then sent to
transmitting station for uploading.
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Control Segment III
Three
transmitting
stations
are
involved for transmitting recent data
(including broadcast message) to
satellites.
These stations also send telemetry commands
for repositioning, switching spare components
etc.
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User Segment
•Consists of GPS receiver units with capability to obtain real
time positioning.
•GPS receivers are hand-held radio-receivers/computers
which measure the
• time that the radio signal takes to travel from a GPS satellite
until it arrives at the GPS antenna.
Using the travel time multiplied by the speed of light provides
a calculation of range
to each satellite in view. From this and additional information
on the satellites orbit and velocity,
the internal GPS receiver software calculates its position
through a process of resection.
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Advantages of GPS
•Unlike conventional surveying procedures, there is no need for intervisibility between stations.
•Independent of weather conditions as a result of using radio frequencies to transmit the signals.
•Use of same field and data reduction procedures results in position accuracy which
•independent of network
•shape or geometry and are primarily a function of inter-station distance.
•GPS surveying provides generally homogeneous accuracy. Hence,
•geodetic network planning in the classical sense is
•longer relevant. The points can be established wherever they are required
•need not be located at evenly distributed sites
•atop mountains to satisfy intervisibility, or network geometry criteria.
•GPS surveying is more efficient, more flexible and less time consuming positioning
•technique than using conventional terrestrial survey technologies.
•GPS can be used to obtain high accuracy three dimensional (3D) information, anywhere and
•time with relatively little effort on a global datum .
The GPS instrumentation and the data processing software do not radically
even if very high or moderately high accuracies are required (from 1 part in 104 to 1 part in 106 ).
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Applications
•Natural resources
•Precision farming
•Civil Engineering applications
•Structural deformations
•Open pit mining
•Land and marine seismic surveying
•Airborne mapping
•Seafloor mapping
•Vehicle navigation
•Transit system
•Retail industry
•Cadastral surveying
•Stakeout (waypoint navigation)
Location based services (LBS)
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GPS Observativations
◦ Carrier phases
◦ Differential GPS
◦ Relative positioning
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Sources of Error in GPS Surveying
◦ Clock error
◦ Atmospheric inferences
◦ Multipath
◦ Satellites configuration
◦ Instrument setup
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GPS Surveying Techniques
◦ Static
◦ FastStatic
◦ Post-processed Kinematic
◦ RTK
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Post Processing
◦ Data transfer between controller
and office computer
◦ Using office software to process
and adjust data
◦ Import and export data and
graphs to CAD and GIS programs
◦ Generate drawings and reports
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The Continuously Operating
Reference Stations (CORS)
◦ The Network
◦ CORS Data File
◦ Use of CORS in GPS Surveying
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Setting auto time features
Viewing satellite graphs
Editing a session
Defining and viewing curtains
Designing a network
Static surveying
FastStatic surveying
Post-processed Kinematic surveying
Setting up and configuring the radio for
RTK
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Real-Time Kinemeatic (RTK) surveying
Performing site calibration
Staking out a point
Performing GPS survey with CORS
Data transfer
Creating and configuring a processing
style
Processing baseline
Performing network adjustment
Importing and exporting to CAD and GIS
software
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Learning outcomes:
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Describe the principles of GPS surveying.
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Perform planning and network design.
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Setup a GPS system for surveying.
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Perform Post-processed and RTK surveys and
acquire appropriate GPS data.
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Perform data transfer.
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Post process the GPS data.
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Perform error analysis of the acquired GPS and
other measured data.
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Generate field notes appropriate to GPS
surveying.
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Produce written reports to communicate results
of field surveys.
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Assignments
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Review the history of GPS surveying.
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Explain the advantages of GPS surveying.
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Estimate the accuracy of GPS surveying.
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Study the three segments of the GPS
surveying.
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Differentiate the types of receivers.
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Determine the coordinates of a point in
space when the distance between the
point and a known point is given.
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Determine distance with code-ranging
method.
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Assignments
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Determine distance with carrier-phase
method.
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Explain how the integer of ambiguity is
resolved in carrier-phase measurement.
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Explain relative positioning and differential
GPS.
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Study the sources of errors in GPS surveying.
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Explain Static, FastStatic, Post-processed
Kinematic and RTK surveys, their accuracies
and applications.
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Design networks.
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Textbooks
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Chris Rizos, Principles and Practice of GPS
Surveying, UNSW 1997
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Paul Wolf, Elementary Surveying, Prentice Hall,
2002
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Alfred Leick, GPS Satellite Surveying, 2nd ed.,
Wiley, 1995
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Simon McElroy, Getting Started with GPS
Surveying, GPSCO, 1996
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Abdie Tabrizi, Lecture notes, 2004
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Trimble Training Manuals, 2005
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