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Hydrographic surveying
Published in David R. Green, Jeffrey L. Payne, Marine and Coastal Resource Management, 2017
The Earth is an irregular shape, modelled by a sphere on any manageable, physical ‘Globe’ but better represented mathematically by a spheroid, shorter in the polar axis by 21 km than across the equator. The figure of the Earth best known today is often referred to as World Geodetic System 1984 (WGS84) or, more properly, GRS80, i.e. that associated with the US global satellite positioning system, GPS. The long availability of GPS means that much data is gathered with reference to GRS80 or may be transformed from that to a local mapping system.
Co-ordinate reference systems
Published in Martin Vermeer, Antti Rasila, Map of the World, 2019
Geodetic Reference System 1980 (GRS80) was approved by the IUGG, the International Union of Geodesy and Geophysics, in its General Assembly of 1979 in Canberra, Australia. Its defining parameters (e.g., Heikkinen, 1981) are presented in Table 10.1.
Using AUSGeoid2020 and its error grids in surveying computations
Published in Journal of Spatial Science, 2019
W. E. Featherstone, J. C. McCubbine, S. J. Claessens, D. Belton, N. J. Brown
First, some minor technical clarifications: AUSGeoid2020 is strictly neither a geoid model nor a quasigeoid model. The computation of AGQG2017 delivered a gravimetric-only quasigeoid model, but this was subsequently tilted (cf. Featherstone and Filmer 2012) and surface-fitted to GPS-AHD heights across the continent using least squares prediction (Brown et al. 2018a). As such, its physical-geodetic definition in terms of the Earth’s gravity field is somewhat nebulous; instead, it gives a model of the separation between the AHD and GRS80 ellipsoid (cf. Featherstone 1998), realised as GDA2020. In the following, we use the symbol to describe the AUSGeoid2020 GDA2020-AHD separation solely because this symbology is more familiar to GNSS users for height determination, but use when referring to AGQG2017 (Appendix A and Section 2.2). Featherstone and Kuhn (2006) review these subtleties of heights in the Australian context.
Description and release of Australian gravity field model testing data
Published in Australian Journal of Earth Sciences, 2018
W. E. Featherstone, N. J. Brown, J. C. McCubbine, M. S. Filmer
These relative vertical deflections have since been converted to absolute values (i.e. with respect to the geocentric GRS80 ellipsoid) and used for gravity field model testing in a variety of guises over Australia: the global EGM2008 (Pavlis et al., 2012, table 9) and regional quasigeoid models (Featherstone, 2006; Featherstone & Morgan, 2007; Featherstone et al., 2017), assessment of satellite-derived geoid models (Hirt et al., 2011), and even in an attempt to fit a regional quasigeoid model to them (Featherstone & Lichti, 2009). However, the historical nature of vertical deflections makes them prone to larger uncertainty (cf. Featherstone & Olliver, 2013).
A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Vaughan Stagpoole, Craig Miller, Fabio Caratori Tontini, Thomas Brakenrig, Nick Macdonald
Gravity data, including data acquired on Lake Taupō (Davy and Caldwell 1998), were reprocessed using Gsolve software (McCubbine et al. 2018) to generate free air and Bouguer anomalies with respect to the GRS80 reference ellipsoid parameters (Moritz 1980). The global free air gradient 0.3086 mGal/m is used for elevation corrections. A density of 2670 kg/m3 is used for Bouguer and terrain corrections to account for the gravitational effect of topography above mean sea level out to a radius of 120 km from each gravity observation point. An additional correction is applied to the Lake Taupō data to account for the density of the large water body.