North American height datums and their offsets: Evaluation of the GOCE-based global geopotential models in Canada and the USA

Amjadiparvar, Babak; Sideris, Michael G.; Rangelova, Elena

doi:10.1515/jag-2012-0033

Cited by 5 publications

(2 citation statements)

References 6 publications

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“…Since the global cumulative geoid error provided by the DIR5 model is smaller than that of the TIM5 model, it has been decided to use the DIR5 model as the GOCE-based GGM in the numerical computations of this study. For a comprehensive investigation on the performance of the earlier and recent GOCE-based models in North America, the reader is referred to the work by Amjadiparvar et al (2013b) and Sideris et al (2015), respectively. The geoid heights in the following sections are computed by the DIR5 model and its combination with the EGM2008 model, abbreviated as ExtDIR5, to take the omission error of DIR5 into account (see Sect.…”

Section: Global Geopotential Modelsmentioning

confidence: 99%

The GBVP approach for vertical datum unification: recent results in North America

Amjadiparvar

Rangelova

Sideris

2015

J Geod

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Two levelling-based vertical datums have been used in North America, namely CGVD28 in Canada and NAVD88 in the USA and Mexico. Although the two datums will be replaced by a common and continent-wide vertical datum in a few years, their connection and unification are of great interest to the scientific and user communities. In this paper, the geodetic boundary value problem (GBVP) approach is studied as a rigorous method for connecting two or more vertical datums through computed datum offsets from a global equipotential surface defined by a GOCEbased geoid. The so-called indirect bias term, the effect of the GOCE geoid omission error, the effect of the systematic levelling datum errors and distortions, and the effect of the geodetic data errors on the datum unification are four important factors affecting the practical implementation of this approach. These factors are investigated numerically using the GNSS-levelling and tide gauge stations in Canada, the USA, Alaska, and Mexico. The results show that the indirect bias term can be omitted if a GOCE-based global geopotential model is used in gravimetric geoid computations. The omission of the indirect bias term simplifies the linear system of equations for the estimation of the datum offset(s). Because of the existing systematic levelling errors and distortions in the Canadian and US levelling networks, the datum offsets are investigated in eight smaller regions along the Canadian and US coastal areas. Using GNSSlevelling stations in the US coastal regions, the mean datum offset can be estimated with a 1 cm standard deviation if the GOCE geoid omission error is taken into account by means of the local gravity and topographic information. In the Cana-B B. Amjadiparvar

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Section: Global Geopotential Modelsmentioning

confidence: 99%

The GBVP approach for vertical datum unification: recent results in North America

Amjadiparvar

Rangelova

Sideris

2015

J Geod

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“…6 show that although when the unmodified Stokes kernel is used the indirect bias term exceeds 40 cm, this term drops to sub-cm level when the residual kernel corresponding to the n max used for the GM-contribution is used (n max D 180 was used in this case as the GM error increased when TIM4 was used with higher maximum degrees; see Amjadiparvar et al 2013). In fact for any n max 70, the indirect effect was found to be below 1 cm.…”

Section: Computation Of the Terms In The Multi-datum Gbvp Solutionmentioning

confidence: 99%

Geodetic World Height System Unification

Sideris

2014

Handbook of Geomathematics

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Elevations are one of the positional attributes embedded in all geospatial data. They are essential for a wide range of engineering and scientific activities. Some of the activities requiring precise elevations are activities of high societal impacts, such as sea level rise, storm surges and coastal inundation, floods and evacuation route planning, and crustal motion, subsidence, and other surface deformations due to seismic, mining, or other events. In order to successfully monitor and manage such events regionally (e.g., floods) or globally (e.g., sea level rise), the elevation information needs to not only be accurate but to also refer to the same zero-height reference surface (vertical datum). Accurate elevations can be obtained using spirit leveling, or by combining Global Navigation Satellite Systems (GNSS) positioning methods with a model of the geoid (the equipotential surface of the Earth's gravity field approximating the idealized mean sea surface). So although the high accuracy requirements can in general be met, the need for a common reference surface often cannot. This is because there are currently over 100 different vertical datums around the world. Their unification is therefore a scientific problem of high practical significance.Height system unification is the process of determining the offsets between existing vertical datums, each of which is defined with a fundamental zero-elevation point and the equipotential (level) surface of the Earth's gravity field that passes through that point. These offsets can be estimated if the geodetic (from GNSS), physical (from spirit leveling), and geoid (from gravity information) heights are known for the fundamental and/or other points in each datum. GNSSsurveyed leveling benchmarks on land, GNSS-surveyed tide gauge stations at the coasts, and a mean dynamic topography model at sea can be used as data, together with a geoid model. The need to estimate geoid undulations implies the solution of a geodetic boundary value problem (GBVP); see, e.g., Colombo (1980), Rummel and Teunissen (1988), Rapp and Balasubramania (1992), Venuti (2002), andMoritz (2013). Although normal heights and height anomalies from the solution of Molodensky's GBVP can and have been used for datum unification, here we work with orthometric heights and geoid undulations from the solution of the classical (Stokes) GBVP. We first review briefly the key concepts of leveling and vertical datum definition and realization, and then discuss, in spherical approximation, the single (global) vertical datum GBVP and the multiple vertical datum GBVP following primarily the developments of Rummel and Teunissen (1988). We also introduce the functional and stochastic models used for the least-squares estimation of datum offsets and their accuracies. Using an example from North America with tide gauges, we address a few important practical aspects, such as the magnitude of the so-called indirect bias term resulting from the use of biased local gravity data, and the commission and omission geoid un...

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Evaluation of GOCE-Based Global Geopotential Models Versus EGM2008 and GPS/Levelling Data in Northwest of Turkey

Avsar

Erol

Kutoğlu

2015

International Association of Geodesy Symposia

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North American height datums and their offsets: Evaluation of the GOCE-based global geopotential models in Canada and the USA

Cited by 5 publications

References 6 publications

The GBVP approach for vertical datum unification: recent results in North America

The GBVP approach for vertical datum unification: recent results in North America

Geodetic World Height System Unification

Evaluation of GOCE-Based Global Geopotential Models Versus EGM2008 and GPS/Levelling Data in Northwest of Turkey

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