Towards worldwide height system unification using ocean information

Abstract

We describe the application of ocean levelling to worldwide height system unification. The study involves a comparison of ‘geodetic’ and ‘ocean’ approaches to determination of the mean dynamic topography (MDT) at the coast, from which confidence in the accuracy of stateof- the-art ocean and geoid models can be obtained. We conclude that models are consistent at the sub-decimetre level for the regions that we have studied (North Atlantic coastlines and islands, North American Pacific coast and Mediterranean). That level of consistency provides an estimate of the accuracy of using the ocean models to provide an MDT correction to the national datums of countries with coastlines, and thereby of achieving unification. It also provides a validation of geoid model accuracy for application to height system unification in general. We show how our methods can be applied worldwide, as long as the necessary data sets are available, and explain why such an extension of the present study is necessary if worldwide height system unification is to be realised.

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

“…Part of that work involves using coastal tide gauge data as a check of the consistency of variation of MSL along the coast with knowledge of the geoid and of the coastal MDT, the latter provided either by numerical ocean circulation models or by more general oceanographic insight. Such checks for the North American Pacific, Gulf of Mexico and Atlantic coastlines and the European Atlantic coastline have been made by Higginson (2012), Woodworth et al (2012) and Higginson et al (2015). Similar studies for the Australian coastline have been made by Featherstone and Filmer (2012) and Filmer (2014).…”

“…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.…”

“…Woodworth et al 2012). The coastal MDT is also of interest to geodesists for which a long-standing objective has been the construction of a World Height System (WHS), which in effect means the use of a precise model of the geoid as a reference datum, replacing the many individual national datums based on MSL (Rummel 2012).…”

“…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.…”

Comparisons at Tide-Gauge Locations of Glacial Isostatic Adjustment Predictions with Global Positioning System Measurements

“…Wöppelmann and Marcos (2016) give an excellent description of this topic. A third example is in the pursuit of worldwide height system unification, whereby all future heights will be measured in a geocentric reference frame by techniques such as GNSS and altimetry and all countries will use a unified datum, which is in effect the geoid (Woodworth et al, 2012). We know of no 'activists and politicians'.…”