Australian quasigeoid modelling: Review, current status and future plans

We provide a historical review and critique of regional geoid and quasigeoid modelling over the Australian continent, covering the earliest models from the late 1960s through to the present day and beyond. The most recently released official model for GPS/GNSS surveyors, AUSGeoid2020, was specifically calculated to enable them to determine Australian Height Datum heights from Geocentric Datum of Australia 2020 ellipsoidal heights in a more direct manner without the need for post-surveying adjustments. We summarise the deficiencies in the Australian Height Datum and how they are now being addressed by a proposed new vertical height system that is underpinned by a gravimetric-only quasigeoid model. We also summarise the results of some experiments that we have conducted to explore potential refinements that could be made to our computational processes, and future plans to acquire gravity data in the problematic coastal zones using airborne methods

Potentially Misleading GPS Leveling-Based Assessment of Gravimetric Geoid or Quasigeoid Models due to Vertical Land Motion and Different GPS Processing Software

© 2019 American Society of Civil Engineers. Gravimetric geoid or quasigeoid models are often evaluated using Global Positioning System (GPS) and leveling, but the veracity of these control data is not always considered. Using a precisely surveyed 40-km-long traverse of 62 points in Perth, Western Australia, we exemplify that vertical land motion and the choice of GPS processing software may lead to spurious conclusions as to which is the best model, particularly with regard to the assessment in the presence of tilts among these data sets. We recommend that the effect of vertical land motion (if present) be factored into such evaluations, GPS data be processed using the same software and in the same reference frame, and tilts among the data sets be considered during the evaluations

Coastal gravity field refinement by combining airborne and ground-based data

© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Gravity field modelling in coastal region faces challenges due to the degradation of the quality of altimeter data and poor coverage of gravimetric measurements. Airborne gravimetry can provide seamless measurements both onshore and offshore with uniform accuracies, which may alleviate the coastal zone problem. We study the role of airborne data for gravity field recovery in a coastal region and the possibility to validate coastal gravity field model against recent altimetry data (CryoSat-2, Jason-1, and SARAL/Altika). Moreover, we combine airborne and ground-based gravity data for regional refinement and quantify and validate the contribution introduced by airborne data. Numerical experiments in the Gippsland Basin over the south-eastern coast of Australia show that the effects introduced by airborne gravity data appear as small-scale patterns on the centimetre scale in terms of quasi-geoid heights. Numerical results demonstrate that the combination of airborne data improves the coastal gravity field, and the recent altimetry data can be potentially used to validate the high-frequency signals introduced by airborne data. The validation against recent altimetry data demonstrates that the combination of airborne measurements improves the coastal quasi-geoid, by ~ 5 mm, compared with a model computed from terrestrial and altimetry-derived gravity anomalies alone. These results show that the recently released altimetry data with relatively denser spatial resolutions and higher accuracies than older altimeter data may be beneficial for gravity field model assessment in coastal areas

Evaluating temporal stability of the New Zealand quasigeoid following the 2016 Kaikōura earthquake using satellite radar remote sensing

Quasigeoid models can be determined from surface gravity anomalies, so are sensitive to changes in the shape of the topography as well as changes in gravity. Here we present results of forward modelling gravity/quasigeoid changes from synthetic aperture radar data following the 2016 Mw 7.8 Kaikōura earthquake with land uplift of up to 10 m. We assess the impact of the topographic deformation on the reference surface of the New Zealand vertical datum in lieu of costly field gravity field measurements. The most significant modelled gravity and quasigeoid changes are-2.9 mGal and 5-7 mm, respectively. We compare our forward modelled gravity signal to terrestrial gravity observation data and show that differences between the data sets have a standard deviation of ±0.1 mGal. The largest modelled change in the quasigeoid is an order of magnitude smaller than the 57.7 mm estimated precision of the most recently computed NZGeoid model over the Kaikōura region. Modelled quasigeoid changes implied by this particular deformation event are not statistically significant with respect to estimated precision of the New Zealand quasigeoid model