Abstract
The performance of Earth Gravitational Model 2008 (EGM2008) is evaluated over Nairobi County and its environs using GPS/levelling and free-air gravity anomalies. The data used include 18 GPS/levelling and 97 gravity points. The heights in Kenya are referred to the mean sea level and they are generally considered as orthometric heights. Hence the height anomalies obtained from tide-free EGM2008 model are converted to geoid undulations using a conversion model supplied with EGM2008. The standard deviation of the differences between EGM2008 implied and GPS/levelling geoid undulations at the 18 points is ±11.6 cm while the standard deviation of the differences between EGM2008 implied free-air and observed free-air gravity anomalies at the 97 points is ±10.7 mGal. These results indicate a high potential for EGM2008 in geoid modelling over Kenya. An initial high-resolution gravimetric geoid model over Kenya can be developed by combining EGM2008 and local gravity data sets. Keywords: EGM2008, geoid undulations, free-air gravity anomalies, GPS/levelling, Nairobi County and its environs
Highlights
The Earth Gravitational Model 2008 (EGM2008) model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159
The free-air gravity anomalies and geoid undulations implied by EGM2008 are computed at various spectral bands - 30 degrees interval between 0 to 180 degrees and 180 degrees interval between 180 to 2190 degrees
An assessment of EGM2008 has been carried out using geoid undulations and free-air gravity anomalies over Nairobi County and its environs
Summary
The EGM2008 model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159. It is supplied with a conversion model complete to degree and order 2160 for converting height anomalies to geoid undulations (Pavlis et al, 2012). Several authors have evaluated EGM2008 in different parts of the world Other assessment studies (25 in number) are presented in Newton’s Bulletin (2009). Most of the comparative studies show that EGM2008 has made significant improvement over EGM96. Such studies have not been carried out in Kenya
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