Wednesday: 16:00-17:30 Rocco Malservisi: e-mail malservisi@geophysik.uni-muenchen.de 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. Lecture 1 May 3rd 2006 Eratosthenes (215 BC) S=4400 stadia ~787km Q=7.2 C=39376km R~ 6267 km Lecture 1 May 3rd 2006 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 Lecture 1 May 3rd 2006 TRADITIONAL SURVEY Horizontal positioning TRILATERATION Lecture 1 May 3rd 2006 TRADITIONAL SURVEY Horizontal positioning TRAVERSE EDM Lecture 1 May 3rd 2006 TRADITIONAL SURVEY Vertical positioning GEODETIC LEVELING TRIGONOMETRIC HEIGHTING Lecture 1 May 3rd 2006 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 Quic kT i me™ and a T IFF (Unc ompres s ed) dec ompres s or are needed t o s ee thi s pi c ture. QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. Lecture 1 May 3rd 2006 QuickTime™ and a TIF F (Uncompressed) decompressor are needed to see this picture. 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. Lecture 1 May 3rd 2006 InSAR • Two or more data acquisition of the same area from nearby location (< 1000 m) • Enables detection of surface changes within cm level accuracy Lecture 1 May 3rd 2006 Lecture 1 May 3rd 2006