Global Navigation Satellite Systems
Dr. Antonios Mouratidis
Remote Sensing and GIS Applications Laboratory, Department of Physical and Environmental Geography, School of Geology,
Aristotle University of Thessaloniki, Greece [email protected]
ESA SAR Course The Malta Council for Science and Technology
Malta, 10 - 14 November 2014
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Contents
Definition, purpose and components of a GNSS
How does a GNSS work?
Receivers and measurement methods
GNSS datum (Horizontal/Vertical)
Aspects of accuracy
Overview of applications
Useful links
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What is a GNSS?
Stands for Global Navigation Satellite System
GNSS >> GPS (erroneously used instead of GNSS)
Several GNSSs (US, Russia, Europe, China…)
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Current and near-future GNSSs
The term “Global Positioning System (GPS)” has (had?)
prevailed historically, practically and conceptually…
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What is a GNSS?
(Scientific American, February 1996)
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Purpose of a GNSS
Determines:
- Time
- Position (φ, λ, h coordinates)
- Speed
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Space segment (Satellite constellation)
Control segment
Users
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Components of a GNSS
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At least 4 satellites visible at all times
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How does a GNSS work?
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Satellite Based Augmentation Systems (SBAS)
Is a civil aviation safety-critical system
Supports regional, even continental augmentation through
the use of geostationary satellites which broadcast the
augmentation information
Augments primary GNSS constellation(s) by providing GEO
ranging, integrity and correction information.
The main goal of SBAS is to provide integrity assurance
It also increases the accuracy with position errors below 1
meter (1 sigma).
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SBASs
European Geostationary Navigation Overlay Service/EGNOS
(Europe)
Wide Area Augmentation System/WAAS (U.S.)
Multi-functional Satellite Augmentation System/MSAS and
the Quasi-Zenith Satellite System/QZSS (Japan)
System for Differential Corrections and Monitoring /SDCM
(Russia)
GPS Aided Geo Augmented Navigation/GAGAN (India)
Satellite Navigation Augmentation System/SNAS (China)
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SBASs
("SBAS Service Areas" by Persimplex - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:SBAS_Service_Areas.png#mediaviewer/File:SBAS_Service_Areas.png)
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GNSS Receivers
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Measurement Methods
Static Kinematic
Absolute or relative positioning (…although there is no such thing as “absolute”)
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GNSS data
WGS 84 ellipsoid
Lat/Lon coordinates
Ellipsoidal height (h)
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GNSS Elevation/Height measurements
Ellipsoid
Geoid (MSL)
Actual (topographical) surface
h=H+N h: geometric (geodetic) height
H: orthometric (topographic) height
N: geoid height
GNSS measures h !!!
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Accuracy
Up to a few mm, depending on:
- Type of receiver
- Method
- Duration of observations
- Distance
- Atmospheric conditions
- Overall measurement conditions
Reliability
Acc
urac
y High Low
Hig
h
Low
(Source: www.despair.com)
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Accuracy
Vertical accuracy (Z) about x 2.5 times lower that
that of horizontal (X, Y)
The cause lies in geometry
Some receivers are equipped with a barometric
altimeter for improving the vertical accuracy
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“Strong” Geometry
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“Weak” Geometry
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“Visibility”
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Applications
Military
Surveying/Geodesy
Navigation
Cartography
Construction
Geosciences
…many more…
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…more applications
Source: Navipedia (http://www.navipedia.net)
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ESA NAVIPEDIA
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http://www.navipedia.net/index.php/Main_Page
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http://www.gsa.europa.eu/
