Abstract:
Gravity information is vital for many geodetic and geophysical studies. One
of the fundamental geodetic applications of gravity data is geoid
determination. GPS-leveling data is also an important source of information
for precise geoid determination. Since geoid reflects density distribution of
Earth’s internal masses, it can be used for geophysical investigations.
However, high quality and dense gravity and GPS-leveling data are not
available for many developing countries due to financial and physical
difficulties.
In order to examine this issue, alternative methods, based on latest high
quality global gravity and digital terrain models, are proposed for precise
geoid determination and its geophysical interpretations, especially for
regions where the required survey networks are not sufficient. In geoid
determination, long and medium wavelength gravity field structures are
determined from the recent global gravity field model, the Earth
Gravitational Model 2008 (EGM2008), while the short wavelength
structures are calculated from the global digital terrain model (the Shuttle
Radar Topography Mission (SRTM) elevation data). Residual topography
reduced geoid undulation differences between GPS-levelling and EGM2008
are modeled as a trend and a corrective surface separately. The long
wavelength component of the gravity field of the geoid obtained by filtering
in various aspects is subsequently employed for Moho depth determination.
For numerical analysis, different test areas are employed based on terrain
conditions and data availability. The comparison and validation of the
computed geoids in the Canadian and Sri Lankan regions are carried out
using the available geoid and GPS-levelling data. The results suggest that
the computed geoid models in both regions are able to be used to support
GPS-levelling in the third order height networks. The results of Moho depth computation in the test area of USA are in a good agreement with
seismically determined Moho depths than those obtained by global Moho
models.
