The north‐south tilt in the Australian Height Datum is explained by the ocean's mean dynamic topography

We review the measurement of the mean dynamic topography (MDT) of the Mediterranean using ellipsoidal heights of sea level at discrete tide gauge locations, and across the entire basin using satellite altimetry, subtracting estimates of the geoid obtained from recent models. This 'geodetic approach' to the determination of the MDT can be compared to the independent 'ocean approach' that involves the use of in situ oceanographic measurements and ocean modelling. We demonstrate that with modern geoid and ocean models there is an encouraging level of consistency between the two sets of MDTs. In addition, we show how important geodetic MDT information can be in judging between existing global ocean circulation models, and in providing insight for the development of new ones. The review makes clear the major limitations in Mediterranean data sets that prevent a more complete validation, including the need for improved geoid models of high spatial resolution and accuracy. Suggestions are made on how a greater amount of reliable geo-located tide gauge information can be obtained in the future. IntroductionThis paper discusses the mean dynamic topography (MDT) of the Mediterranean and its measurement by geodetic techniques. The MDT is the amount by which the Mean Sea Surface (MSS) is further from the centre of the Earth than a surface called the geoid, which is an equipotential surface resulting from the Earth's spatially-varying gravity field, and which would correspond to the MSS in the absence of an ocean circulation. An accurate measurement of the MDT can, therefore, provide oceanographers with insight into the circulation. Conversely, knowledge of the circulation, obtained by a number of oceanographic techniques can be used to infer the MDT. 2Much is already known about the mean circulation of the Mediterranean and its variability (e.g. Pinardi and Masetti 2000) and, therefore, also about the spatial variation of its MDT. This insight has largely been obtained using in situ oceanographic measurements and ocean modelling. However, in recent years major advances have been made in geodetic techniques that have enabled the MDT to be determined, for the first time, as the difference between MSS and geoid to the accuracy required for oceanographic research (e.g. Bingham et al. 2014). These techniques have primarily involved satellite altimetry to provide the MSS over the open ocean and space gravity to provide the geoid, complemented at the coast with the use of tide gauges equipped with Global Positioning System (GPS) equipment (Woodworth et al. 2012). By studying the Mediterranean, particular lessons can be learned in the use of these techniques, notably by pointing to missing infrastructure and data limitations, which can also be relevant to discussion of the MDT in other data-sparse regions around the world.Models of the MDT in the Mediterranean have already been made by previous authors in various ways (e.g. Rio et al. 2014a). Consequently, the present paper focuses on reviewing how an MDT model can be compa...

Section: Mdt Values At Mediterranean Tide Gaugesmentioning

confidence: 98%

“…Featherstone and Filmer 2012;Woodworth et al 2012), it was possible to access the required tide gauge, GPS and local levelling information at a large number of sites. However, it will be seen that this is far from being the case for the Mediterranean.…”

Section: Overview Of Existing Mediterranean Geodetic Infrastructurementioning

confidence: 99%

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques

Woodworth

Gravelle

Marcos

et al. 2015

“…Without solving for a bias and tilted plane, CARS has a STD <±0.10 m at 0.5 degree cap radius, whereas the MC_NC and MC_NOC are both >±0.15 m and AHD >±0.18 m. When solving for a bias and tilted plane, the AHD STD decreases to ±0.10 m, while CARS decreases to ±0.09 m, indicating that CARS has already removed most of the AHD's MDTinduced tilt (cf. Featherstone and Filmer 2012). MC_NOC and MC_NC STD decrease to ±0.12 m, but reflect that regional distortions rather than a systematic north-south tilt contribute to errors in these LSAs.…”

Section: Modified Stokes Parameter Sweepsmentioning

confidence: 99%

“…This is dominated by a north-south tilt (cf. Featherstone and Filmer 2012) but with some regional distortions. The geometric component was converted to a free-air gravity term and modified-Stokes-integrated using the parameters in Sect.…”

Section: Gravity Datamentioning

confidence: 99%

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

Featherstone

McCubbine

Brown

et al. 2017

Self Cite

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.

“…In Australia, for instance, the vertical datum contains a confirmed tilt with respect to the geoid (Featherstone and Filmer 2012), regional distortions [e.g., Featherstone et al (2011) and the citations therein], and uses a height system that is not compatible with the geoid (Filmer et al 2010). These will cause errors in the computed terrestrial gravity anomalies (cf .…”

mentioning

confidence: 99%

Deterministic, stochastic, hybrid and band-limited modifications of Hotine’s integral

Featherstone

2013

Self Cite