Abstract
This study carries out an evaluation of the recent high-degree combined global gravity-field models (EGM2008, EIGEN-6C4, GECO and SGG-UGM-1) over Kenya. The evaluation is conducted using observed geoid undulations (18 data points, mainly in Nairobi area) and free-air gravity anomalies (8,690 data points, covering the whole country). All the four models are applied at full spherical harmonic degree expansion. The standard deviations of the differences between observed and GGMs implied geoid undulations at 18 GPS/levelling points over Nairobi area are ±11.62, ±11.48, ±12.51 and ±11.75 cm for EGM2008, EIGEN-6C4, GECO and SGG-UGM-1, respectively. On the other hand, standard deviations of the differences between observed and GGMs implied free-air gravity anomalies at 8,690 data points over Kenya are ±10.11, ±10.03, ±10.19 and ±10.00 mGal for EGM2008, EIGEN-6C4, GECO and SGG-UGM-1, respectively. These results indicate that the recent high-degree global gravity-field models generally perform at the same level over Kenya. However, EIGEN6C4 performs slightly better than EGM2008, GECO and SGG-UGM-1, considering the independent check provided by GPS/levelling data (admittedly over a small area). These results further indicate a good prospect for the development of a precise gravimetric geoid model over Kenya using EIGEN-6C4 by integrating local terrestrial gravity data in a removecompute-restore scheme.
Highlights
High-degree combined global gravity-field models (GGMs) are realized from optimal combination of satellite, terrestrial and altimetry-derived gravity datasets
Most of the free-air gravity anomalies can be recovered by the high-degree GGMs at ±10 mGal (79.2, 79.3, 79.3 and 79.6% for EGM2008, GECO, EIGEN-6C4 and SGGUGM-1, respectively) and ±20 mGal (95.4, 95.5, 95.7 and 95.7% for EIGEN-6C4, EGM2008, SGG-UGM-1 and GECO, respectively)
This study presents an initial evaluation of the recent highdegree global gravity-field models (EGM2008, EIGEN6C4, GECO and SGG-UGM-1) over Kenya using geoid undulations and free-air gravity anomalies
Summary
High-degree combined global gravity-field models (GGMs) are realized from optimal combination of satellite, terrestrial and altimetry-derived gravity datasets. The high-degree combined global gravity-field models evaluated in this study include EGM2008 (Pavlis et al, 2012), EIGEN-6C4 (Förste et al, 2014), GECO (Gilardoni et al, 2016) and SGG-UGM-1(Liang et al, 2018). These models are principally developed from GOCE data (in the long-to-medium wavelength components) and EGM2008 (in the mediumto-short wavelength components). LAGEOS data are included in the development of EIGEN-6C4
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