1 Geoid and Geoid Change: Discussion Topics Roger Haagmans, Boulder, 21October 2009.
The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges –...
Transcript of The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges –...
![Page 1: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/1.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1
A preliminary attempt of a quasi‐geoid for Saudi Arabia
Saad Mogren1 & D. Blitzkow2 1King Saud University, College of Sciences, Geology & Geophysics
Department, Saudi Arabia. 2Laboratory of Topography and Geodesy Department of Transportation,
University of São Paulo EPUSP‐PTR, CEP:05424‐970 São Paulo, São Paulo, Brazil
The Proposed Quasi‐Geoid Project
• Undertake a national geoid (quasi‐geoid) model study for Saudi Arabia
• To fully utilize the three dimensional location satellite technology • Replace many aspects of conventional topographic surveying by
accurate, rapid and cost effective satellite based methodology. • The aims and scope of this study are to generate a high resolution
geoid model for Saudi Arabia with suitable accuracy for rapid and efficient surveying methods related to Geodesy and Engineering (e.g. levelling for water distribution and flow, dams, roads and railways etc).
• The expected accuracy will be in Absolute: better than 0.5 m and relative: approximately 0.1cm per km
![Page 2: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/2.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 2
Geoid
• Geoid is the equi‐potential surface of the Earth gravity field that best approximates the mean sea level
• Is the most natural shape of the earth
• It serves as the reference surface for most of the height system.
Why Quasi‐Geoid
• Saudi Arabia is rough in the West and has large lateral density variations in crust.
• Using constant density value for the crust is a well‐known assumption in determination of the geoid models, however:
• Large lateral density variation effect the geoid.
![Page 3: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/3.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 3
Topography of the Study Area
Methodology
• Helmert gravity anomaly computed from a compilation of all existing gravity
• In the computations, a reference field provided by a suitable geopotential model, like GRACE, will be removed from the anomalies. In the end the long wavelength component will be restored to the quasi‐geoid heights using the same geopotential model.
• Once the geoid has been derived, it can be used with GNSS data to accurately estimate the normal height of a point very quickly and efficiently. This can eliminate the need for conventional levelling which is costly and time consuming.
![Page 4: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/4.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 4
Quasi‐Geoid
• Quasi‐Geoid was implemented some countries as a practical alternative to geoid estimations which is constrained by gravity lateral variations within the Earth and therefore the orthometric height derived by geoid model requires a precise observation of gravity anomalies above the sea level which is practically undetectable.
• However, in the quasi‐geoid modeling an approach was first introduced by Molodensky where he solved the geodetic boundary value problem by refereeing the gravity anomalies to the ground. This new Quasi‐Geoid estimation approach was applied adequately in some countries:
• Iran (Kiamehr, 2008), and Belgium (Barzaghi et al., 2003). And New Zealand (Amos and Featherstone, 2009).
• This technique is an effective part of Dubai Virtual Reference System (Dubai VRS) that uses real time positioning from GPS satellites signals at the cm accuracy in major civil engineering applications. Coupled with the newly developed quasi‐geoid model (El‐Mowafy et al. 2006).
Gravity Coverage
ARGAS •1973 to 1975, •Three Fundamental Gravity Base Stations (FGBS) were established in Riyadh, Jeddah and Jizan, and interconnected to three IGSN 1971 bases in Beirut, Cairo and Asmara. •A total of 3579 readings were collected. •905 stations were re‐observed showing a mean standard error of 0.048 mGal •USGS •Start 1974 to 1977. •accuracy of ±0.15 mGal
![Page 5: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/5.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 5
Tie to IGSN71
Bouguer Anomaly
![Page 6: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/6.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 6
The Resultant Quasi Geoid Compared To EGM2008
Difference From EGM2008
![Page 7: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/7.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 7
Regional Tectonic Signature
Results & Suggestions
• Poor resultant Geoid due to poor Gravity Coverage.
• Quasi‐Geoid should be tested against GPS/Leveling.
• Establishing First‐order Absolute‐Gravity network using the Micro‐g FGL or FG5 Absolute Gravimeter.
• Tying the existing networks of GPS and gravity with the new Absolute Gravity network.
• Densifing Gravity points in areas with no Gravity surveys like some part of the Arabian Shield.
![Page 8: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/8.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 8
Thank You
• The orthometric height, is the length of the curved plumbline therefore the following should be known:
• The exact path of the plumbline through the Earth • The gravitational acceleration at all points along that plumbline need to be known.
• Also knowledge of the mass‐density distribution through the topography
• However, • these parameters are not available, therefore it is not possible to observe or compute a true orthometric height, despite what many people seem to believe.
Orthometric Height
![Page 9: The Proposed Quasi Geoid Project...30‐04‐2010 FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 1 A preliminary attempt of](https://reader033.fdocuments.us/reader033/viewer/2022060602/60560ae1d062121b0a504d3c/html5/thumbnails/9.jpg)
30‐04‐2010
FIG Congress 2010 Facing the Challenges – Building the Capacity Sydney, Australia, 11‐16 April 2010 9
Normal Height • The normal gravity field can be used to define a height that avoids Density Measurements
• It is defined geometrically as the distance along the ellipsoidal surface normal from the reference ellipsoid to the telluroid