Precise geoid determination and its geophysical implications in Sri Lanka

Abstract

Gravity information is vital for many geodetic and geophysical studies. One of the fundamental geodetic applications of gravity data is geoid determination. GPS-levelling data is also an important source of information for precise geoid determination. However, high quality and dense gravity and GPS-levelling data are not available for many developing countries due to financial and physical difficulties. In this study, 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 some geophysical studies such as Moho depth and lithospheric structure 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. The estimated lithospheric geological structure beneath the Sri Lankan region is consistent with the main crustal units of Sri Lanka which fits well to different ancient plates.