The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

Abstract

We describe the computation of the first Australian quasigeoid model to include error estimates as a function of location that have been propagated from uncertainties in the EGM2008 global model, land and altimeterderived gravity anomalies and terrain corrections. The model has been extended to include Australia's offshore territories and maritime boundaries using newer datasets comprising an additional ∼280,000 land gravity observations, a newer altimeter-derived marine gravity anomaly grid, and terrain corrections at 1 × 1 resolution. The error propagation uses a remove-restore approach, where the EGM2008 quasigeoid and gravity anomaly error grids are augmented by errors propagated through a modified Stokes integral from the errors in the altimeter gravity anomalies, land gravity observations and terrain corrections. The gravimetric quasigeoid errors (one sigma) are 50-60 mm across most of the Australian landmass, increasing to ∼100 mm in regions of steep horizontal gravity gradients or the mountains, and are commensurate with external estimates.

Using AUSGeoid2020 and its error grids in surveying computations

“…The error grid that accompanies AUSGeoid2020 GDA2020-AHD separations results from a linear combination of the errors from AGQG2017 (Featherstone et al, 2018), the published AHD heights and the GDA2020 ellipsoidal heights (Brown et al, 2018a); cf. Eq.…”

“…This was deliberate so as to account for errors originating from all data sources contributing to AUSGeoid2020. These were computed at all ~7,500 points scattered across the continent (Featherstone et al, 2018, Figure 6d) then gridded at a 1'x1' resolution using the same covariance parameters for the least squares prediction used to generate AUSGeoid2020. This has caused the errors in AUSGeoid2020 to be, on average, ~40 mm larger than the errors from AGQG2017 (cf.…”

“…Featherstone, 1998). Like its predecessor, AUSGeoid09 (Brown et al, 2011;Featherstone et al, 2011), AUSGeoid2020 has fitted the AGQG2017 gravimetric-only quasigeoid model (Featherstone et al, 2018) to ~7,500 GPS-AHD heights across the continent using least squares prediction (Brown et al, 2018a,b). AUSGeoid2020 is also accompanied by a grid of vertical deflections/deviations computed from the horizontal gradients of AGQG2017.…”

AUSGeoid2020 combined gravimetric–geometric model: location-specific uncertainties and baseline-length-dependent error decorrelation

“…4b) was computed by SLOPOV-propagating that of the geometric component and AGQG2017 ( Fig. 12a in Featherstone et al 2018a), assuming independence. The uncertainty in AUSGeoid2020 is dominated by the uncertainty in the AHD heights, which results in a larger error estimate in AUSGeoid2020 than AGQG2017.…”

“…Roelse et al 1975;Morgan 1992;Featherstone 2004Featherstone , 2006Featherstone and Filmer 2008;Featherstone 2009, 2012). This paper describes the fitting of the Australian Gravimetric Quasigeoid 2017 model (AGQG 2017;Featherstone et al 2018a) to a nationwide GPS-levelling dataset (Featherstone et al 2018b) to provide a model of the separation between the GDA2020 ellipsoid and the AHD, thus enabling a direct transformation between ellipsoidal and AHD heights (cf. Featherstone 2000).…”