Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
GNSS is a satellite-based positioning system
that enables accurate positioning, navigation,
and timing.
There are several GNSS systems in operation
around the world:
• GPS (USA)
• GLONASS (RUSSIA)
• Galileo (EU)
• BeiDou (CHINA)
• QZSS (JAPAN)
• IRNSS (INDIA)
5/31/2023 CB573 Page 46
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
Advantages of satellite positioning system:
• No need for inter-visibility
• No distance limitations
• GNSS has the flexibility to work under any condition 24 hours a day
• High Geodetic Accuracy
• Common Coordinate System
• In productivity , great time saving as compared with conventional
surveying techniques
• At least 50 % cost reduction as compared with conventional
surveying techniques
• GNSS has numerous applications in land, marine, air navigation, etc.
5/31/2023 CB573 Page 47
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
GNSS consist of three major
components or “segments:” the
space segment, the control
segment and the user segment.
5/31/2023 CB573 Page 48
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
1. Space segment
• The space segment consists of GNSS satellites orbiting 19,000 to 36,000
kilometres above the Earth.
• Each GNSS has its own constellation of satellites, arranged in orbits to
provide the desired coverage.
• Each satellite in a GNSS constellation broadcasts a signal identifying itself
and providing its precise time, orbit location and system health status.
5/31/2023 CB573 Page 49
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
2. Control segment
• The control segment consists of a network of ground-based control stations
that track the satellites and responsible for maintaining the GNSS satellites.
• In each GNSS system, the master control station adjusts the satellites’ orbit
parameters and onboard high-precision clocks when necessary to maintain
accuracy.
• The master control station analyses the signals and transmits orbit and time
corrections to the satellites through data uploading stations.
Control segment of GPS
5/31/2023 CB573 Page 50
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
3. User segment
The user segment consists of equipment that
processes the received signals from the GNSS
satellites and uses them to derive and apply location
and time information.
• Handheld Receivers / Mobile Devices / Car
Navigation
• Single Frequency Receivers (One Signal)
• Dual Frequency Receivers (Two Signals)
• Multi Frequency / Multi Constellation Receivers
• Special Receiver and Antenna Designs
5/31/2023 CB573 Page 51
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
In concept, the 3D coordinates of a point can be determined using
simultaneous observed ranges to the known satellites positions. Such a
process is similar to the so called “RESECTION PROBLEM” in surveying.
5/31/2023 CB573 Page 52
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
Satellite Ranging (Measuring the distance from a satellite)
• By measuring travel time of code signals
Multiply that time by 300,000 km/sec (CODE RANGE)
• By measuring the phase of carrier signals
Multiply that phase by the carrier wavelength (PHASE RANGE)
5/31/2023 CB573 Page 53
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
Code (Pseudorange) Observations
Each satellite sends a unique signal.
Receiver compares self generated signal with the received signal.
From the time difference (∆𝑻) a range observation can be determined.
Receiver clock needs to be synchronized with the satellite clock.
P(T)= 𝒄 ∗ ∆𝑻 = 𝒄 ∗ [𝒕𝒓𝒆𝒄 − 𝒕𝑺𝒂𝒕 ]
5/31/2023 CB573 Page 54
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
Carrier Phase Observations
• Receiver compares self-generated phase with the received phase.
• Number of wavelengths is not known at the time the receiver is switched on
(carrier phase ambiguity).
• As long as you track the satellite, the change in distance can be observed
(the carrier phase ambiguity remains constant).
L= 𝛌 ∗ ∅
5/31/2023 CB573 Page 55
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
𝑷 = 𝝆 + 𝒄 𝒅𝒕𝒓 − 𝒅𝒕𝒔 + 𝑬𝒓𝒓𝒐𝒓𝒔
𝑷= (𝑿𝒔 − 𝑿𝒓 )𝟐 +(𝒀𝒔 − 𝒀𝒓 )𝟐 +(𝒁𝒔 − 𝒁𝒓 )𝟐 + 𝒄 𝒅𝒕𝒓 − 𝒅𝒕𝒔 + 𝑬𝒓𝒓𝒐𝒓𝒔
𝑿𝒔 , 𝒀𝒔 , 𝒁𝒔 : computed from the ephemeris file
c : 299792458 m/s
𝒅𝒕𝒔 : computed from the ephemeris file
𝑬𝒓𝒓𝒐𝒓𝒔 : can be modelled to eliminate or mitigate
𝑿𝒓 , 𝒀𝒓 , 𝒁𝒓 , 𝒅𝒕𝒓 : UNKNOWNS
To solve the model for 4 Unknowns, we need at least 4 Equations
At least, FOUR SATELLITES To Use GPS
5/31/2023 CB573 Page 56
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
5/31/2023 CB573 Page 57
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
1. Static Point Positioning
• Accuracy is low.
• Usually used in navigation applications.
5/31/2023 CB573 Page 58
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
2. Static Relative Positioning
• Uses (at least) two receivers
One located at a known point
One used to determine position of
unknown point
• Typically uses carrier phase
measurements.
• Determine the vector between known
point and unknown point.
• Very High accuracy (few millimeters).
• Used for national and continental
networks applications.
5/31/2023 CB573 Page 59
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
3. Kinematic Technique
“Kinematic" surveying is needed to
determine the position of the antenna
while it is moving.
Used for Topographic maps and road
survey in open areas
5/31/2023 CB573 Page 60
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
4. Real Time Kinematic (RTK)
• Typically uses carrier phase measurements.
• Correction signal is sent by a Radio Link
• Few centimeters accuracy
Used when:
The survey involves large number of unknown
points 10-15 km from the known point
The coordinates of the unknown points are
required in real time.
The line of sight is relatively unobstructed.
5/31/2023 CB573 Page 61
Arab Academy for Science & Technology & Maritime Transport
College of Engineering & Technology
Construction & Building Engineering Department
5/31/2023 CB573 Page 62
