Height systems and vertical datums: A review in the Australian context

Featherstone, Will; Kühn, Michael

doi:10.1080/14498596.2006.9635062

Cited by 59 publications

(45 citation statements)

References 43 publications

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“…As an aside on terminology, AUSGeoid98 was a geoid model, but Australia is more suited to the use of a quasigeoid model because the AHD uses a normal-orthometric height system (e.g., Featherstone and Kuhn 2006). Since the normal-orthometric height system used in the AHD (Roelse et al 1971) does not use any gravity observations, it is theoretically and practically inconsistent with a quasigeoid model, with the largest differences between normal and normal-orthometric heights reaching ~0.2 m in the Australian Alps .…”

Section: Motivationmentioning

confidence: 99%

The AUSGeoid09 model of the Australian Height Datum

Featherstone

Kirby

Hirt

et al. 2010

J Geod

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Abstract. AUSGeoid09 is the new Australia-wide gravimetric quasigeoid model that has been a posteriori fitted to the Australian Height Datum (AHD) so as to provide a product that is practically useful for the more direct determination of AHD heights from Global Navigation Satellite Systems (GNSS). This approach is necessary because the AHD is predominantly a third-order vertical datum that contains a ~1 m north-south tilt and ~0.5 m regional distortions with respect to the quasigeoid, meaning that GNSS-gravimetricquasigeoid and AHD heights are inconsistent. Since the AHD remains the official vertical datum in Australia, it is necessary to provide GNSS users with effective means of recovering AHD heights. The gravimetric component of the quasigeoid model was computed using a hybrid of the remove-compute-restore technique with a degree-40 deterministically modified kernel over a one-degree spherical cap, which is superior to the remove-compute-restore technique alone in Australia (with or without a cap). This is because the modified kernel and cap combine to filter long-wavelength errors from the terrestrial gravity anomalies. The zero-tide EGM2008 global gravitational model to degree and order 2190 was used as the reference field. Other input data are: ~1.4 million land gravity anomalies from Geoscience Australia, 1'x1' DNSC2008GRA altimeter-derived gravity anomalies offshore, the 9"x9" GEODATA-DEM9S Australian digital elevation model, and a readjustment of Australian National Levelling Network (ANLN) constrained to the CARS2006 dynamic ocean topography model. In order to determine the numerical integration parameters for the modified kernel, the gravimetric component of AUSGeoid09 was compared with 911 GNSS-observed ellipsoidal heights at benchmarks. The standard deviation of fit to the GNSS-AHD heights is ±222 mm, which dropped to ±134 mm for the readjusted GNSS-ANLN heights, showing that careful consideration now needs to be given to the quality of the levelling data used to assess gravimetric quasigeoid models. The publicly released version of AUSGeoid09 also includes a geometric component that models the difference between the gravimetric quasigeoid and the zero surface of the AHD at 6,794 benchmarks. This a posteriori fitting used least-squares collocation (LSC) in cross-validation mode to determine a correlation length of 75 km for the analytical covariance function, whereas the noise was taken from the estimated standard deviation of the GNSS ellipsoidal heights. After this LSC surface-fitting, the standard deviation of fit reduced to ±30 mm, one third of which is attributable to the uncertainty in the GNSS ellipsoidal heights.

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Section: Motivationmentioning

confidence: 99%

The AUSGeoid09 model of the Australian Height Datum

Featherstone

Kirby

Hirt

et al. 2010

J Geod

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“…Featherstone and Kuhn, 2006). However, the accurate computation of the cumulative normal to normal-orthometric height correction to levelled height differences is restricted (in the absence of observed gravity data along levelling lines) by the cumulative effect of the GGM commission and omission errors especially in mountainous regions of New Zealand with large spatial gravity and elevation gradients.…”

Section: Methodsmentioning

confidence: 99%

Combined approach for the unification of levelling networks in New Zealand

Tenzer

Vatrt²,

Gan

et al. 2011

Journal of Geodetic Science

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Abstract:The unification of levelling networks in New Zealand is done using a combined approach. It utilises the joint levelling network adjustment and the geopotential-value approach. The levelling and normal gravity data are used for a joint adjustment of the levelling networks at the South and North Islands of New Zealand while fixing the heights of tide gauges in Dunedin and Wellington. The results reveal a good quality of levelling data; the STD of residuals is 2 mm for the whole country. The comparison of the newly determined and original normal-orthometric heights confirms the presence of large local vertical datum offsets and systematic levelling errors. Since the geopotential-value approach is based on the Molodensky's theory, the newly adjusted normal-orthometric heights are converted to the normal heights. This conversion is based on applying the cumulative normal to normal-orthometric height correction computed from levelling and gravity anomaly data. In the absence of the observed gravity data the gravity anomalies along levelling lines are generated from EGM2008. The GPS-levelling data and EGM2008 are used to estimate the average offsets of the jointly adjusted levelling networks at the North and South Islands with respect to World Height System defined by the adopted geoidal geopotential value of W 0 = 62636856 ± 0 5 m 2 s −2 ; the estimated offsets are 10.6 cm and 27.5 cm. we refer readers to Gilliland (1987). The LVDs were defined in the system of the (approximate) normal-orthometric heights.The cumulative normal-orthometric correction to levelled height differences was defined based on the GRS67 normal gravity field parameters and computed approximately using a truncated form of the GRS67 normal-orthometric correction formula (Rapp, 1961).Since LVDs were referenced to the local mean sea level (

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“…A transformação de números geopotenciais para medidas de altitudes requer a divisão deste por um valor específico da gravidade, o qual definirá os diferentes tipos de altitudes físicas. Assim, todos os sistemas de altitudes natural/físico são baseados neste princípio (FEATHERSTONE et al, 2006). A busca de uma solução unívoca para a altitude de um ponto P pode ser definida por meio de uma altitude cientifica (H C ), onde G é o valor particular de gravidade considerado.…”

Section: Geopotencial E Altitudesunclassified

“…Nos trabalhos de Luz (2004); Kingdon et al (2005); Amos et al (2005); Featherstone e Kuhn (2006); Christie (1994); Kouba (2006); Véronneau e Héroux (2007), são abordadas questões altimétricas como o modelo de altitudes adotado e a sua vinculação a um datum vertical nos seus respectivos contextos locais, sendo em alguns destes trabalhos, propostas soluções para o problema da definição de um novo referencial vertical na área estudada.…”

Section: Introductionunclassified

Estudo das correções gravimétricas para altitudes físicas aplicadas aos desníveis da RAAP

et al. 2013

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RESUMOA adoção de uma rede altimétrica consistente constitui uma importante necessidade dentro da modernização do sistema geodésico nos contextos brasileiro e sulamericano. Atualmente na Rede Altimétrica de Alta Precisão (RAAP) do Brasil aplica-se aos desníveis observados uma correção aproximada devido o não paralelismo das superfícies equipotenciais de forma a reduzir este erro, porém esta condição não assegura um significado físico para as altitudes. Buscando apresentar uma solução unívoca para a realização de sistemas altimétricos adota-se as altitudes físicas, as quais são fundamentadas no conhecimento do potencial da gravidade (W), baseado em importantes condições definidoras de um sistema vertical moderno. O presente trabalho tem como objetivo determinar e avaliar a magnitude das correções das altitudes dinâmica, ortométrica de Helmert e normal em uma linha de nivelamento pertencente à RAAP situada na região nordeste do estado do Rio Grande do Sul em um trajeto que possui 1.179,73 m de desnível. Os resultados obtidos na correção dos desníveis observados para as altitudes dinâmicas,

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Height systems and vertical datums: A review in the Australian context

Cited by 59 publications

References 43 publications

The AUSGeoid09 model of the Australian Height Datum

The AUSGeoid09 model of the Australian Height Datum

Combined approach for the unification of levelling networks in New Zealand

Estudo das correções gravimétricas para altitudes físicas aplicadas aos desníveis da RAAP

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