Transcript Document

Wednesday: 16:00-17:30
Rocco Malservisi:
e-mail [email protected]
phone 21804202
Class Web page: www.geophysik.lmu.de/~malservisi/TectGPS.html
Lecture 1 May 3rd 2006
From Greek: “ DIVIDING THE EARTH ”`
“Geodesy is the branch of applied
mathematics concerned with the
determination of the size and shape of
the Earth, with the exact positions of
points on its surface, and with the
description of variations of its gravity
field.”
Lecture 1 May 3rd 2006
International Association of Geodesy definition
How big is the
Earth?
Which is the shape
of the planet?
How tall is a
mountain?
Where my property ends?
Lecture 1 May 3rd 2006
Where am I?
How far am I from a place?
In which direction
should I go?
How big is my property?
If we want to have a mathematical representation of a
point (point’s coordinate) we need to have a reference
surface we can refer to.
Knowing the shape of the Earth we can define this
surface.
The gravity field gives the best representation of the
shape of the Earth.
Lecture 1 May 3rd 2006
The Earth is “almost” a sphere with a circumference ~40000 km long
The meter was defined using this length.
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Eratosthenes (215 BC)
S=4400 stadia ~787km
Q=7.2 C=39376km
R~ 6267 km
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XVII XVIII Century Discussion of Oblate-Prolate spheroid
Cassini meridian south of France shorter than in Paris
PROLATE
British Pendulum slower at equator and Newton equations
OBLATE
XVIII Century (1730) Expedition of France Academy:
Peru measurement: 6376.45 km (Equatorial Radius)
Lapland measurement: 6355.88 km (Polar Radius)
OBLATE!!
Difference: 1350m in 111km!!!
Lecture 1 May 3rd 2006
The Earth is “almost” a sphere with a circumference ~40000 km long
The meter was defined using this length.
Better approximate by an oblate ellipsoid
Today accepted Value
Equatorial Radius
6378 km
Polar Radius
6357 km
Sphere of Equal Volume Radius
6371 km
Flattening
1/298.257223563
Lecture 1 May 3rd 2006
The “real” shape of the planet is approximated by the Geoid:
THE EQUIPOTENTIAL SURFACE
AT THE MEAN SEA LEVEL
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Lecture 1 May 3rd 2006
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
We can divide geodesy
According to what
we observe
According to method
Space Geodesy
use of extra-terrestrial
object as observable.
Terrestrial Geodesy
Use of terrestrial tools
And observable
Lecture 1 May 3rd 2006
OR
Global Geodesy
Determination of shape of
the Earth, global references.
Geodetic Survey
Determination of positions,
and references over a region
for which the Earth’s curvature can have influences.
Plane Survey
Determination of positions
and references on a local
level.
TRADITIONAL SURVEY
Horizontal positioning
Vertical positioning
TRIANGULATION
GEODETIC LEVELING
TRILATERATION
TRIGONOMETRIC
HEIGHTING
TRAVERSING
ASTRONOMICAL
POSITIONING
BAROMETRIC
LEVELING
TILTING
Lecture 1 May 3rd 2006
TRADITIONAL SURVEY
Horizontal positioning
TRIANGULATION
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TRADITIONAL SURVEY
Horizontal positioning
TRILATERATION
Lecture 1 May 3rd 2006
TRADITIONAL SURVEY
Horizontal positioning
TRAVERSE
EDM
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TRADITIONAL SURVEY
Vertical positioning
GEODETIC LEVELING
TRIGONOMETRIC
HEIGHTING
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SPACE SURVEY
VLBI
Very Long Baseline Interferometry
SLR
GPS
Satellite Laser Ranging
Global Positioning System
Glonass
Galileo
DORIS
InSAR Interferometric Synthetic Aperture Radar
Lecture 1 May 3rd 2006
Very Long Baseline
Interferometry
VLBI is a geometric technique:
• It measures the time difference
between the arrival at two
Earth-based antennas of a radio
wavefront emitted by a distant
quasar.
• Using large numbers of time
difference measurements from
many quasars observed with a
global network of antennas,
VLBI determines the inertial
reference frame defined by the
quasars and simultaneously the
precise positions of the
antennas.
Lecture 1 May 3rd 2006
SLR
Satellite Laser Ranging
QuickTime™ and a
TIFF(Uncompres sed) decompressor
are needed t o see this pict ure.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF(Uncompres sed) decompressor
are needed t o see this pict ure.
Lecture 1 May 3rd 2006
The Global Positioning System
• The Global Positioning System (GPS) is
a satellite-based navigation system.
• GPS was originally intended for military applications, but
in the 1980s, the government made the system available
for civilian use.
• GPS works in any weather conditions, anywhere in the
world, 24 hours a day. There are no subscription fees or
setup charges to use GPS
• Some civilian uses:
– Navigation on land, sea, air
and space
– Geophysics research
– Guidance systems
– Geodetic network densification
– Hydrographic surveys
Lecture 1 May 3rd 2006
Glonass
GLObal NAvigation Satellite System
Glonass is a Soviet space-based navigation system comparable
to the American GPS system.
The operational system contains 21 satellites in 3 orbital planes,
with 3 on-orbit spares.
Glonass provides 100 meters accuracy with its C/A
(deliberately degraded) signals and 10-20 meter accuracy with
its P (military) signals.
Lecture 1 May 3rd 2006
DORIS
Doppler Orbitography and
Radio positioning Integrated by
Satellite
Precise orbit determination and
location system using Doppler
shift measurement techniques.
A global network of 52 Doris
orbitography beacons has been
deployed. Doris was developed
by Cnes, the French space
agency, and is operated by CLS.
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InSAR
• Two or more data acquisition
of the same area from nearby
location (< 1000 m)
• Enables detection of surface
changes within cm level
accuracy
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Lecture 1 May 3rd 2006