On the downward continuation stability in dependence of the topography roughness
21/09/2016 | 11:30 | Session 3: Recent Development in Theory and Modelling
Author(s): Otakar Nesvadba and Petr Holota
Otakar Nesvadba and Petr Holota
The paper describes a procedure for the local/regional quasigeoid modelling based on terrestrial gravity data. The methodology discussed concerns the solution of the gravimetric boundary value problem. We consider its particular formulation for an ellipsoidal domain (the exterior to an oblate spheroid), i.e. gravity disturbances are assumed on an ellipsoidal surface.
The difference between the Earth's topography and an ellipsoidal surface is often solved by a downward (analytical) continuation method of gravity disturbances. Nevertheless, the continuation method seems to be difficult to converge, especially in rough mountainous terrains. Our approach, therefore, combines the continuation of the data related to a smoother reference boundary with the direct gravity reduction (i.e. remove-compute-restore technique) of the masses between the true topography surface and the reference boundary.
We study the sequences of analytical continuation steps in dependence of model topography roughness. The aim is to determine an optimal reference topography which enables to estimate the limit of the sequence and, on the other hand, is sufficiently close to the true Earth’s surface in order to decrease modelling uncertainty sourced in unknown rock mass densities.
The performance of the analytical continuation for different topographies is illustrated on the real-case examples related to the territory of France (Auvergne regional quasigeoid).