JSG T.28

JSG T.28: Regional geoid/quasi-geoid modelling – Theoretical framework for the sub-centimetre accuracy

Chairs: Jianliang Huang (Canada)
Affiliation: Comm. 2 and GGOS

Problem statement

A theoretical framework for the regional geoid/quasi-geoid modelling is a conceptual structure to solve a geodetic boundary value problem regionally. It is a physically sound integration of a set of coherent definitions, physical models and constants, geodetic reference systems and mathematical equations. Current frameworks are designed to solve one of the two geodetic boundary value problems: Stokes’s and Molodensky’s. These frameworks were originally established and subsequently refined for many decades to get the best accuracy of the geoid/quasi-geoid model. The regional geoid/quasi-geoid model can now be determined with an accuracy of a few centimeters in a number of regions in the world, and has been adopted to define new vertical datum replacing the spirit-leveling networks in New Zealand and Canada. More and more countries are modernizing their existing height systems with the geoid-based datum. Yet the geoid model still needs further improvement to match the accuracy of the GNSS-based heightening. This requires the theory and its numerical realization, to be of sub-centimeter accuracy, and the availability of adequate data.

Regional geoid/quasi-geoid modelling often involves the combination of satellite, airborne, terrestrial (shipborne and land) gravity data through the remove-compute-restore Stokes method and the least-squares collocation. Satellite gravity data from recent gravity missions (GRACE and GOCE) enable to model the geoid components with an accuracy of 1-2 cm at the spatial resolution of 100 km. Airborne gravity data are covering more regions with a variety of accuracies and spatial resolutions such as the US GRAV-D project. They often overlap with terrestrial gravity data, which are still unique in determining the high-degree geoid components. It can be foreseen that gravity data coverage will extend everywhere over lands, in particular, airborne data, in the near future. Furthermore, the digital elevation models required for the gravity reduction have achieved global coverage with redundancy. A pressing question to answer is if these data are sufficiently accurate for the sub-centimeter geoid/quasi-geoid determination. This study group focuses on refining and establishing if necessary the theoretical frameworks of the sub-centimeter geoid/quasi-geoid.

Objectives

The theoretical frameworks of the sub-centimeter geoid/quasi-geoid consist of, but are not limited to, the following components to study:

• Physical constant GM
• W0 convention and changes
• Geo-center convention and motion with respect to the International Terrestrial Reference Frame (ITRF)
• Geodetic Reference Systems
• Proper formulation of the geodetic boundary value problem
• Nonlinear solution of the formulated geodetic boundary value problem
• Data type, distribution and quality requirements
• Data interpolation and extrapolation methods
• Gravity reduction including downward or upward continuation from observation points down or up to the geoid, in particular over mountainous regions, polar glaciers and ice caps
• Anomalous topographic mass density effect on the geoid model
• Spectral combination of different types of gravity data
• Transformation between the geoid and quasi-geoid models
• The time-variable geoid/quasi-geoid change modelling
• Estimation of the geoid/quasi-geoid model inaccuracies
• Independent validation of geoid/quasi-geoid models
• Applications of new tools such as the radial basis functions

Program of activities

• The study group achieves its objectives through organizing splinter meetings in coincidence with major IAG conferences and workshops if possible.
• Circulating and sharing progress reports, papers and presentations.
• Presenting and publishing papers in the IAG symposia and scientific journals.

Members

Jianliang Huang (Canada), chair
Yan Ming Wang (USA), vice-chair
Riccardo Barzaghi (Italy)
Heiner Denker (Germany)
Will Featherstone (Australia)
René Forsberg (Denmark)
Christian Gerlach (Germany)
Christian Hirt (Germany)
Urs Marti (Switzerland)
Petr Vaníček (Canada)