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Topic: Geoid

Related Topics

Physical geodesy

Geodetics

Geodesy

Spherical Earth

Reference ellipsoid

Sea level

Mascon

World Geodetic System

Ellipsoid

Erdmessung

Model

Spheroid

Precession of the equinoxes

Tidal locking

	Geoid - Encyclopedia.WorldSearch (Site not responding. Last check: 2007-08-19)
		A geoid is a close representation, physical model, of the figure of the Earth.
		The geoid surface is more irregular than the ellipsoid of revolution often used to approximate the shape of the physical Earth, but considerably more smooth than the Earth's physical surface.
		Spherical harmonics are often used to approximate the shape of the geoid.
	encyclopedia.worldsearch.com /geoid.htm (448 words)

	Earth's Geoid (Site not responding. Last check: 2007-08-19)
		Geoid: The geoid is a representation of the surface of the earth that it would assume if the sea covered the earth, also known as surface of equal gravitational attraction and mean sea level.
		The vertical coordinate, Z (elevation), is referenced to the geoid.
		Geoid Anomaly: A change in the height of a portion of the geoid compared to its height for the majority of the body.
	solid_earth.ou.edu /notes/geoid/earths_geoid.htm (1677 words)

	Geoid - Wikipedia, the free encyclopedia
		The geoid surface is more irregular than the ellipsoid of revolution often used to approximate the shape of the physical Earth, but considerably smoother than Earth's physical surface.
		While the latter has excursions of +8,000 m (Mount Everest) and −11,000 m (Mariana Trench), the geoid varies by only about ±100 m about the reference ellipsoid of revolution.
		Because the force of gravity is everywhere perpendicular to the geoid (being an equipotential surface), sea water, if left to itself, would assume a surface equal to it—even through the continental land masses if sea water were allowed to freely penetrate them, e.g., by tunnels.
	en.wikipedia.org /wiki/Geoid (379 words)

	1-Mean Sea Level, GPS, and the Geoid
		That the earth does not have a geometrically perfect shape is well established, and the geoid is used to describe the unique and irregular shape of the earth.
		By definition, the geoid describes the irregular shape of the earth and is the true zero surface for measuring elevations.
		Although for practical purposes, at the coastline the geoid and MSL surfaces are assumed to be essentially the same, at some spots the geoid can actually differ from MSL by several meters.
	www.esri.com /news/arcuser/0703/geoid1of3.html (1094 words)

	WESSEL ET AL.: PACIFIC GEOID AND BATHYMETRY UNDULATIONS
		Systematic filtering has revealed geoid anomalies which are preferentially elongated in the east-west direction and have average amplitudes of ~0.3 m and dominant wavelengths of 750 km and 1100 km [Cazenave et al., 1992].
		In this geoid image the lineations are most visible north of the yellow arrow indicating Pacific plate motion as subtle undulations superimposed on the background geoid.
		Traditionally, the relation between large scale geoid anomalies and mantle flow is indirectly inferred from the combination of geoid-topography correlations and fluid-dynamic models; this relation is somewhat nonunique.
	www.soest.hawaii.edu /wessel/papers/1994/GRL_94/grl_94.html (2412 words)

	Geoid and Gravity
		The shape of the Earth is often described by the geoid.
		On land the geoid can be thought of as the level of water in an imaginary canal connected at each end with an ocean.
		The height of the geoid varies by as much as 100 m from the highest to the lowest point (but the water is not running down these "hills" since the geoid is level).
	www.kms.dk /research/geodesy/geoid/geoid_en.html (91 words)

	Geoid (Site not responding. Last check: 2007-08-19)
		At the same time, the geoid is the most graphical representation of the Earth gravity field.
		The geoid surface is described by geoid heights that refer to a suitable Earth reference ellipsoid.
		Geoid heights are relative small.The minimum of some -106 meter is located at the Indian Ocean.
	dgfi2.dgfi.badw-muenchen.de /geodis/GRAV/Geoid.html (122 words)

	Geoscience Australia: Geodesy - N, the Geoid-ellipsoid separation (Site not responding. Last check: 2007-08-19)
		The geoid is an equipotential surface of the Earth's gravity field, which closely approximates mean sea level and is by definition perpendicular to the direction of the gravity vector at all points.
		The geoid is a surface of equal gravity potential which closely approximates mean sea level.
		The separation between the geoid and an ellipsoid is known as the geoid-ellipsoid separation, or N value.
	www.ga.gov.au /nmd/geodesy/ausgeoid/n.jsp (478 words)

	Geoid Modeling Errors (Site not responding. Last check: 2007-08-19)
		The deviations of the geoid from the reference ellipsoid range from -100 m (South of India) to +64 m (near New Guinea).
		For example, the geoid can vary by several meters over a few kilometers in areas where there are ocean trenches or ridges.
		Discrepancies in the spherical harmonic coefficients and truncation of the spherical harmonic expansion produce errors in these models, the majority of which is due to inadequate global observation information at the short spatial scales referred to previously.
	www.tsgc.utexas.edu /topex/geoid.html (224 words)

	Mapping Fundamentals (Mapping Toolbox) (Site not responding. Last check: 2007-08-19)
		For the purposes of map display, the geoid of the Earth is assumed to be an exact ellipsoid.
		The use of the term geoid for this ellipsoid is perhaps peculiar to the toolbox.
		Several other geoid vectors are supported, for models ranging from Everest's 1830 ellipsoid (used for India) to the International Astronomical Union ellipsoid of 1965 (used for Australia).
	www.haystack.edu /computing/matlab6.5/help/toolbox/map/fundm112.html (684 words)

	Altimetry, Ocean Currents and the Marine Geoid MIT/EAPS Altimetry (Site not responding. Last check: 2007-08-19)
		The geoid is the gravitational equipotential of the earth defined, for practical purposes, as that surface to which a resting ocean would conform, and it is thus central to using altimetric data for determining absolute currents.
		Note the large geoid amplitudes of +- 100m as compared to oceanic signals which are of the order of 10cm.
		The residual part not explained by the model was interpreted as geoid error and removed from the mean T/P field in the figure, subsequently.
	puddle.mit.edu /~detlef/altimetry/altimetry.html (1650 words)

	Welcome to Lana Panasyuk website
		To determine how much of this deflection is due to the primary-source (the density contrasts in the mantle) and how much is due to the boundary deflection (the secondary source), we have to know the rheology of the media surrounding a mass anomaly.
		Holding the mass anomaly still, we allow the media to respond to the change in the gravitational field: its free upper surface would be pulled up to equilibrate (to line up) with the equpotential level (effect of self-gravitation).
		What we observe on the Earth surface is the total geoid anomaly (fl solid line), which is the sum of all these contributions from the primary density anomaly (blue), the dynamic topography (magenta), and the self-gravitation (green).
	cfauvcs5.harvard.edu /lana/mantle/geoid.htm (686 words)

	The Geoid Library Page
		Recent investigations toward achieving a one centimeter geoid, presented at GGG2000 session 9 of the IAG Symposium in Banff, Alberta, Canada from July 31 - August 4, 2000.
		Kuroishi, Yuki, 1996: Precise Gravimetric Determination of Geoid in the Vicinity of Japan.
		Milbert, D.G., 1991: An accuracy assessment of the GEOID90 geoid height model for the Commonwealth of Virginia.
	www.ngs.noaa.gov /GEOID/geolib.html (859 words)

	Papers: Bouziane (Site not responding. Last check: 2007-08-19)
		In order to obtain such a geoid, high resolution point or mean gravity field data and topographic information are needed as well as a good spherical harmonic reference model.
		A geoid has been computed over an area covering Algeria using a gravity data file of 12000 gravity points, not homogeneously distributed and an elevation model of 15' x 15'.
		The comparison of the Algerian geoid with the GPS derived geoid heights is not possible due to the almost absence of GPS benchmarks in Algeria.
	www.und.ac.za /und/survey/ssg/bouziane.html (269 words)

	Geoid Inversions
		Their preferred viscosity model, which contains a thin, low-viscosity zone at the base of the upper mantle and an increase in viscosity in the lower mantle, is quite similar in gross features to the preferred model of King and Masters [1992].
		It may be beyond the limit of the data to constrain the thickness of the layer at the base of the mantle because, layer thickness and viscosity contrast trade-off directly.
		A new family of viscosity models, characterized by a high viscosity transition zone that is a factor of 1.5 to 2.5 smaller than the lower mantle, but surrounded by low viscosity layers in the upper mantle and upper 200 km of the lower mantle, fits the observed geoid data equally well.
	www.agu.org /revgeophys/king01/node5.html (519 words)

	Papers: Featherstone
		Geoid solutions on land are often verified using GPS and levelling data.
		Geoid for the geoid's sake or geoid for GPS height determination?
		Long and intermediate geoid errors are thought to reside in the geopotential model.
	www.und.ac.za /und/survey/ssg/feather.html (746 words)

	Geoid Data
		Ensemble assumes all geoid models it imports are given with respect to WGS84 datum.
		OSGM02 is a regional geoid model for latitudes from N49°45'30" to N61°01'00" and longitudes from W09°23'30" to E03°33'30".
		OSGM02 gives real geoid heights only for the land and within a 10 km zone around it but not for the sea (if you try to get geoid heights for the sea the model gives "9999").
	www.javad.com /jns/support/geoid_data.html (746 words)

	Alaska Geoid Heights (GEOID96)
		The computation used 1.1 million terrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996 These data were augmented by gravity data contributions from NIMA (former Defense Mapping Agency).
		The geoid heights are referred to the Geodetic Reference System 1980 (GRS80) ellipsoid.
		It is necessary to subtract 12.0 cm from these values to obtain the geoid undulation between the best-fit global geopotential surface and the GRS80 ellipsoid (both expressed in a tide free system).
	www.ngdc.noaa.gov /seg/gravity/document/html/g96al.shtml (191 words)

	COMPARISON OF GEOID MODELS FOR THE (Site not responding. Last check: 2007-08-19)
		As part of the activities of the Special Working Group on Geoid Models, a comparison of a GPS/levelling-derived geoid with six different geoid models based on global harmonic coefficients has been made for the southwestern Cape Province of South Africa.
		All the gravity models provide very similar representations of the geoid for the southwestern Cape Province; as an example, the EGM-X01 representation is shown in Figure 2.
		In all probability this is the likeliest cause of the major part of the 1m bias between the geoids.
	www.ucalgary.ca /~sideris/SWG/merry.html (949 words)

	Principal Hawaiian Islands Geoid Heights (GEOID96)
		: This 2' geoid height grid for the Principal Hawaiian Islands is distributed as a GEOID96 model.
		The computation used 61,000 terrestrial and marine gravity data held in the National Geodetic Survey gravity data base in July 1996 These data were augmented by gravity data contributions from NIMA (former Defense Mapping Agency).
		This model is a gravimetric geoid in a geocentric, ITRF94(1996.0) reference frame.
	www.ngdc.noaa.gov /seg/gravity/document/html/g96hw.shtml (191 words)

	Geoid (Site not responding. Last check: 2007-08-19)
		The geoid surface is more irregular that the ellipsoid of revolution often used to approximate the shape of the physical Earth, but considerably more smooth than the Earth's physical surface.
		While the latter has excursions of +8,000 m (Mount Everest) and -11,000 m (Marianas Trench), the geoid varies by only approx.
		Similarly if sea water would be allowed to freely penetrate the continental masses, e.g., through tunnels.
	www.theezine.net /g/geoid.html (279 words)

	The official NGS GEOID Page (Site not responding. Last check: 2007-08-19)
		What geoid and deflection models has NGS made in the last decade?
		Comparison of the latest models with other geoid models
		(Projects at least loosely tied to the geoid)
	www.ngs.noaa.gov /GEOID (49 words)

	Sorting It All Out : GEOID -- The LCIDs maligned little brother....
		In Windows, the primary key of this database is the GEOID, and many of the core GEOID values can be found in the Table of Geographic Locations.
		Well, let us say that we made the two settings act as being tied together by default, so that if you changed the locale that by default the GEOID would be changed with it.
		Just as meaningful as 221, which btw seems to be the GeoId for Sweden, according to the.NET SDK sample on GeoId.
	beta.blogs.msdn.com /michkap/archive/2005/02/04/366922.aspx (1515 words)

	[CF-metadata] geoid (Site not responding. Last check: 2007-08-19)
		Dear Brian > If we take the path of including information that identifies the geoid in > standard names then the problem arises of providing a new standard name for > each geoid or horizontal datum reference of interest.
		It seems that we should allow these attributes to be attached > either to variables containing data which requires knowlege of the geoid > for correct interpretation, or to variables that define map projections.
		Presumably we leave it open to the data-writer to decide when the geoid needs to be stated.
	www.cgd.ucar.edu /pipermail/cf-metadata/2003/000315.html (274 words)

	EGM96: The NASA GSFC and NIMA Joint Geopotential Model (Site not responding. Last check: 2007-08-19)
		The EGM96 Geoid Undulation with respect to the WGS-84 Ellipsoid.
		The image is shown on a Robinson projection of the Earth.
		Geoid undulations from N. Pavlis (RITSS/NASA GSFC), and image courtesy of J. Frawley (NASA GSFC)>
	cddis.gsfc.nasa.gov /926/egm96/egm96.html (226 words)

	[No title] (Site not responding. Last check: 2007-08-19)
		Chairperson: Arabelos, D. Editors: Tziavos, I.N.; Vermeer, M. Toward a 10' resolution geoid for South America: a comparison study (Solicited Paper)
		Chairperson: Vermeer, M. Editors: Tziavos, I.N.; Vermeer, M. On the determination of a new Australian geoid
		G075 FIANI, M.; SANNA, G. An estimation of Sardinia Island geoid by analysis of GPS/leveling data
	www.copernicus.org /EGS/egsga/nice98/g11.htm (388 words)

	Geoid Details, Meaning Geoid Article and Explanation Guide
		Geoid Details, Meaning Geoid Article and Explanation Guide
		The above formula produces the Earth's gravitational potential at location, the co-ordinate being the geocentric radius, i.e, distance from the Earth's centre.
		Page Contains Information, Facts Details or Explanation Guide About Geoid
	www.e-paranoids.com /g/ge/geoid.html (384 words)

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