Analysis of the GRAV-D airborne gravity data for geoid modelling
20/09/2016 | 17:30 | Session 3: Local/regional geoid determination methods and models
Author(s): Jianliang Huang, Detang Zhong, Simon A. Holmes, Xiaopeng Li, John W. Crowley, Marc Véronneau, Yanming Wang and Rene Forsberg
Jianliang Huang, Detang Zhong, Simon A. Holmes, Xiaopeng Li, John W. Crowley, Marc Véronneau, Yanming Wang and Rene Forsberg
The Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project aims to cover the US territory by airborne gravity measurements with an extension of about 100 km beyond the US border. As such, GRAV-D provides data blocks in the southern and northwestern parts of Canada; in particular, GRAV-D has measured gravity over the Great Lakes region shared by the two countries for the development of the International Great Lakes Datum of 2020. These airborne gravity data provide important new gravity constraints over the Canada-US border regions. In this study, we analyse GRAV-D data in three blocks across the Canada-US border for geoid modelling using three approaches: 1) the remove-restore Stokes-Helmert approach, 2) the spherical harmonic modelling approach, and 3) the remove-restore residual topographic
modelling approach. Two blocks (EN05 and EN08) are within the Great Lakes region with flat and moderate terrains while the third block (AN04) is across Alaska (USA) and Yukon (Canada) over a rough terrain. GRAV-D has an average flight altitude of about 6 km in the three blocks, in which each survey/cross line spans 240 km to 700 km. The high flight altitude of GRAV-D puts forth two main challenges for geoid modelling: the downward continuation of airborne gravity data and the combination of ground and airborne gravity data. New geoid models are determined over the three blocks and validated against GPS-Levelling data and satellite altimetry tracks over Lake Superior. Preliminary results over Lake Superior suggest that the downward continuation effect reaches more than 100 mGal in absolute value with an RMS of 8 mGal. The geoid heights
updated with the GRAV-D data can reach more than 10 cm without weighting. Validation along satellite altimetry tracks over the lake is yet to be conclusive in this ongoing study at this time of
submission. Updated results will be provided in the presentation.