NEW Sattelite-based positioning (2010) Richard …...Surveying (Time dissemination - astronomy)...
Transcript of NEW Sattelite-based positioning (2010) Richard …...Surveying (Time dissemination - astronomy)...
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Satellite-based positioning
R. Knippers
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Application fields
Surveying
Military operations
Engineering
Vehicle tracking
Flight navigation
Car navigation
Ship navigation
Agriculture
Mapping
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Topics for discussion
� The segments of a satellite-based
positioning system
� GPS, GLONASS and Galileo
� Principle of positioning
� Errors and their sources
� Positional accuracies
� Relative (differential) positioning
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Three segments
� Space segment: the satellites that orbit
the Earth, and the radio signals that they
emit.
� Control segment: the ground stations that
monitor and maintain the space segment
components.
� User segment: the users with their hard-
and software to conduct positioning.
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Space segment of GPS system
The space segment of GPS
consists of 24 satellites on 6
orbits (approx. 22,000 km
from the centre of the Earth):
� Each satellite carries a clock.
� Each satellite completes 2
orbits/day.
� 24 hour complete GPS coverage anywhere on the Earth.
� Accuracy: 21 meters 95% of time
NAVSTAR GPS
Satellite
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L2 CarrierL1 Carrier
P-CodeP-CodeC/A CodeNavigation Message
Navigation Message
1227.60 MHz1575.42 MHz
GPS Signal Structure
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Control Segment of GPS
Space Segment24+ Satellites
Current ephemeris is transmitted to users
Monitor Stations• Diego Garcia
• Ascension Island• Kwajalein
• Hawaii• Colorado Springs
GPS Control Colorado Springs
End User
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Control Segment of GPS
Master Control Station
Monitor Station
Ground Antenna
Colorado
Springs
HawaiiAscension
Islands
Diego
Garcia
Kwajalein
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User segment of GPS
Receivers and their users:
� (Military)
� Navigation in 3D-aircrafts,
� ships, ground vehicles and hand-carried instruments
� Precise positioning -Surveying
� (Time dissemination -
astronomy)
� (Research projects on
atmospheric distortions)
GPS-Receivers
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Selection of a GPS receiver
� Application (boating, flying, driving,
mapping, surveying)
� Accuracy requirements
� Power consumption requirements
� Operational environment
� Signal processing requirements
� Cost
� Data exchange standards
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Space segment of GLONASS system
Russian system
(Globalnaya Navigatsionnaya
Spunikova Sistema - GLONASS)
� 24 satellites (21 operational and 3 spare).
� Three orbital planes at 65ºinclination.
� Two codes as GPS, but all satellites broadcast identical codes but using slightly different carrier frequencies for each satellite.
� The positioning principal is the same as GPS
� Accuracy: 20 m horizontal and ~30 m vertical
GLONASS Satellite
http://www.glonass-ianc.rsa.ru
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Space segment of Galileo system
Galileo is in the implementation
phase, first satellite to be
launched in 2006, planned
operation start 2008.
� Designed for civil purposes
� 30 satellites
� 3 orbits (23,222 km high)
� Network of ground stations, 2 control centresin Europe
� Accuracy of single receiver: around 1 m
http://www.esa.int/esaNA/SEMY02FFWOE_galileo_0.html
Galileo Satellite
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Principle of positioning
GPS-receiver
GPS-satellite
Distance =
(velocity of light) x (travel time)
The GPS-receiver computes the
distances (ranges) to the satellitesThe GPS-receiver computes the
distances (ranges) to the satellites
How does the GPS-receiver
computes the travel time?How does the GPS-receiver
computes the travel time?
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L2 = 1227.60 MHz
L1 = 1575.42 MHz
GPS code on Carrier wave
(C/A or P code)
It receives GPS-codes and
Carrier waves from the satelliteIt receives GPS-codes and
Carrier waves from the satellite
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Code from Satellite
Code from Receiver
Time difference
between
Receiver and Satellite signal
∆t
Code comparison
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Principle of positioning
GPS-receiver
GPS-satellite
Pseudo-range =
(velocity of light) x (travel time)
+ (receiver clock error) + (other errors)
The GPS-receiver measures in fact
pseudo distances (pseudo-ranges) to
the satellites
The GPS-receiver measures in fact
pseudo distances (pseudo-ranges) to
the satellites
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Principle of positioning
(X,Y,Z)
1 2
3
distance 1
distance 2
distance 3
To determine a position in a
3 dimensional space it takes in theory
3 distance measurements from
3 satellites
To determine a position in a
3 dimensional space it takes in theory
3 distance measurements from
3 satellites
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Pseudorange positioning
Three-satellite fix position
(trilateration)
Two-satellite fix position
One-satellite fix position
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(X,Y,Z,∆∆∆∆t)
1
2
3
4
pseudorange 1
pseudo-range 2
pseudo-range 3
pseudorange 4
Pseudorange =
velocity of light * travel time
+ receiver clock error + other errors
Accurate positioning requires
an extra distance measurement
from a fourth satellite to
eliminate the receiver clock error
Accurate positioning requires
an extra distance measurement
from a fourth satellite to
eliminate the receiver clock error
Principle of positioning
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Synchronization bias of the receiver clock
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Error sources in absolute positioning
� Selective availability
� Satellite clock and orbit errors
� Ionospheric and tropospheric delays
� Receiver’s environment (multi-path)
� Satellite constellation
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Receiver’s environment errors
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Magnitude of the error sources*
* Absolute, single-point positioning based on code measurements
*
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Good satellite constellation
Low PDOP (1.5)Good satellite constellation
Low PDOP (1.5)
Bad satellite constellation
High PDOP(5.7)Bad satellite constellation
High PDOP(5.7)
Satellite constellation
positional error
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Positional accuracy in absolute positioning
Absolute, single-point positioning based on code measurements:
Typical error: 5-10 m (horizontal accuracy)
Typical error: 2-5 m (horizontal accuracy) when using a dual-
frequency receiver or the encrypted military signals (P-code)
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Location errors: noise, bias and blunder
� Noise (random) errors:noise in code and noise
in receiver, multi-path.
� Bias (systematic) errors:clock, satellite position,
ionosphere, troposphere,
GDOP effects.
� Blunder: incorrect geodetic datum,
software failures,
hardware problems etc.
Systematic errors (bias) removal is essential to improve the positional accuracy!
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(X,Y,Z) Reference point
Reference (or base) receiver
Target (or field) receiver
Differential (or relative)
positioning
Relative positioning
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Positional accuracy in relative positioning
Relative, single-point positioning based oncode measurements:
Typical error: 0.5 - 5m (horizontal accuracy)
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Positional accuracy in relative positioning
Relative, single-point positioning based oncarrier phase measurements:
Typical error: 2mm – 2cm (horizontal accuracy)
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Carrier phase measurements
Carrier phase measurement is a technique to measure the range
(distance) of a satellite by determine the number of cycles of the
(sine-shaped) radio signal between sender and receiver.
The number of cycles is determined in a long observation session
from the change in carrier phase (Phase Shift Keying). This
change happens because the satellite is orbiting itself.
L1/L2 Carrier
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Relative (differential) survey techniques using carrier phase measurements
� Static
� Stop and go kinematic
� Pseudo-kinematic
� Kinematic
� Rapid static
� On-the-fly (OTF)/real-time kinematic (RTK)
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Real-time kinematic positioning
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Network positioning
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Network positioning Relative positioning using a network of reference stations
NLR Globalcomhttp://www.lnrglobalcom.nl
GlobalNET 2005
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Network positioning GlobalNET 2005: Reference Station at ITC
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Satellite-Based Augmentation
Systems (SBAS)
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(X,Y,Z) Reference point
Ground station
Field receiver(X,Y,Z) Reference point
Ground station
Geostationary satellite
Satellite-based Augmentation Systems
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(X,Y,Z) Reference point
Ground station
(X,Y,Z) Reference point
Ground station
Geostationary satellite
Satellite-based Augmentation
Systems
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Operational systems
� WAAS (Wide-Area Augmentation System)
for North America
� EGNOS (European Geostationary
Navigation Overlay Service) for Europe
� MSAS (Multi-functional Satellite
Augmentation System) for eastern Asia
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WAAS, EGNOS, MSAS
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Wide Area Augmentation System (WAAS)
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Local Area Augmentation System (LAAS)
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INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION
The end !
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INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION
Mobile GIS applications
Data collection with a mobile computer
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INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION
Location-Based Services (LBS)
Location-Based Services on a Mobile
computer or mobile phone.
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INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION
Location-Based Services - Applications
1. Location based information services (e.g. search for the nearest restaurant or the nearest banking cash machine)
2. Location based emergency service (e.g. pinpoint your location on dialing 9-1-1)
3. Location based billing service (e.g. preferential billing for calling by establishing personal zones such as a home zone or work zone).
4. Fleet applications (tracking a vehicle and/or operator).
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INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION
LBS application - Mobile phone tracking
http://geotracing.com/tland