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Document: Monographie

The integration of GPS heights into the Australian Height Datum / R.D. Holloway (1988)

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Titre :	The integration of GPS heights into the Australian Height Datum
Type de document :	Monographie
Auteurs :	R.D. Holloway, Auteur
Editeur :	Kensington [Australie] : University of New South Wales
Année de publication :	1988
Collection :	Unisurv Report num. S-33
Importance :	152 p.
Format :	21 x 30 cm
ISBN/ISSN/EAN :	978-0-85839-051-5
Note générale :	Bibliographie
Langues :	Anglais (eng)
Descripteur :	[Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] altitude orthométrique [Termes IGN] Australie [Termes IGN] méthode des moindres carrés [Termes IGN] nivellement par GPS [Termes IGN] réseau de nivellement [Termes IGN] système de référence altimétrique
Index. décimale :	30.10 Systèmes de référence et réseaux géodésiques
Résumé :	(Auteur) The Global Positioning System (GPS) is being used to determine ellipsoidal height differences (h) over baselines by organisations who are attracted to its efficiencies in use and accuracy of results compared to conventional surveying techniques. For these heights to be physically meaningful they must be integrated into the Australian Height Datum (AHD) to be compatible with other spirit levelled heights (H). The GPS heights are referred to the reference ellipsoid of the satellite system whilst the reference surface of the AHD is observed mean sea level at 30 tide gauges around the Australian coastline being a close approximation of the geoid. The difference between the two surfaces at a point is the geoid-ellipsoid separation (N), or more commonly and more accurately, the difference in the geoid-ellipsoid separation (N) when expressed over a baseline. This study investigates the three components of the equation used to transform GPS heights into the AHD, H = h - N and finds that, * heights in the AHD should be referred to as normal orthometric heights because normal gravity is used in the orthometric correction, * heights in the AHD are referred to a warped surface not coincident with the geoid or any other equipotential surface because the levelling was adjusted between the mean sea level heights at 30 tide gauges around the Australian coastline, * the difference between mean sea level and the geoid at each tide gauge station is equal to the sea surface topography at the tide gauge, * there is a high probability that compensating gross errors in heights remain undetected in some levelling loops. The principal systematic error sources in the GPS heights were found to be, * the troposphere delay error, * the a priori coordinates of the fixed station, * the residual ionosphere delay error, * errors in the satellite ephemerides. Simulation studies show that with an appropriate observation and computation strategy the precision of GPS heights is 2-4 ppm. It was also found that there was no benefit in resolving the cycle ambiguities because the heights were not improved if the integer ambiguities were solved for correctly, which must be weighed against the risk of degrading the heights if the ambiguities are resolved incorrectly. The precision requirements for the computation of the geoid-ellipsoid height differences vary with the application and the remoteness of the location. For the most precise heighting applications it is necessary to compute N to the same precision as that of the GPS heights. The methods investigated in this study include, * geometrical methods such as contouring N values and analytically fitting a plane surface to height control points, * using high order geopotential models such as OSU81, GPM2 and OSU86E, * using ring integration (RINT), which uses a high order geopotential model combined with integration of the local gravity field using Stokes' formula. Each of these methods is evaluated by computing N in two GPS observed networks, one in Western Australia and the other in South Australia. The relative precision of the results and complexity of computation are compared. It was found that GPS heights can be integrated into the AHD without loss of accuracy and that GPS heighting is a viable alternative to spirit levelling for all but the most accurate applications.
Numéro de notice :	63136
Affiliation des auteurs :	non IGN
Thématique :	POSITIONNEMENT
Nature :	Monographie
Permalink :	https://documentation.ensg.eu/index.php?lvl=notice_display&id=61179

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