By Musa Ibrahim
The dedicated satellite gravity missions have provided homogeneous and uniformly accurate information on the long and medium wavelengths of the Earth’s gravity field. The aim of this study is to evaluate the comparative fit of EGM2008, GRACE and GOCE geoid models over Nigeria and to assess the possible improvements to them coming from the recently obtained satellite gravity models. The study is conducted in stages. First, the geoid models computed from the first and the second generation GOCE-only and GRACE-GOCE combined satellite-only models as well as EGM08 are truncated for different spherical harmonic degrees are compared to the Orthometric heights of some points in the Nigerian triangulation network which are reduced to the same spectral band of the gravity field. The Orthometric -derived geoid heights are used as independent controls in the assessment of the geoid models. The comparison results indicate that the GRACE models show a full power of gravity signal in terms of geoid undulation up to about spherical harmonic degree 150. Second, one of the first generation GOCE satellite-only models developed by the time-wise approach, TW01, is complemented with local terrestrial data and tested against the Orthometric height-derived geoid undulations in full spectrum of the gravity field and compared with the official global and regional geoid models does not yield good results. Based on total results there is enough evidence indicating significant improvement (cm level) from the GRACE models to the geoid modeling in Nigeria with 0.892rms and 0.147m or 14.7cm standard deviation over EGM08 and GOCE.