Regional Gravity Field Modelling From Grace Satellite Gravity Mission Data A Case Study In Ethiopia

The Gravity Recovery and Climate Experiment (GRACE) mission data-derived gravity fieldrnmodels have provided us with remarkable accuracy in gravity field determination. Despite this, thernpredicted GRACE baseline accuracy has yet to be met. One reason, among many, could berninsufficient satellite data modeling using a global representation by Spherical Harmonics (SH). Itrnappears appropriate to improve global solutions through regional recovery strategies to fullyrnrecover the signal information included in satellite and sensor data. Varied geographical regionsrnhave different gravity field characteristics, especially in the higher frequency part of the spectrum.rnAs a result, the recovery process should be tailored to the specific characteristics of the area. Thisrnregional refinement strategy was employed in Ethiopia. Global gravity reference field, which isrnrepresented by SH expansion is then refined using regionally tailored refinements that are specifiedrnas space localizing basis functions using splines. The shape coefficients are obtained using thernglobal gravity model's degree error variances truncated up to a maximum degree of 120. Thisrnmeans that the spline kernels must be adjusted to the spectral range of the gravity field features tornbe calculated. In addition, the raw accelerometer data measured by GRACE Satellites usingrnonboard accelerometers was calibrated. Every short arc over the study area is used, with a 10° striprnadded to the recovery area. After being synchronized, these short arcs created a partial system ofrnnormal equations using an integral equation of the Fredholm type. These normal equations arernaccumulated to account for varied accuracies of short arcs by estimating variance factors for eachrnarc using variance component estimation (VCE). For only one month of data collected in Januaryrn2016, the normal equations are solved using the least squares regularized approach. In the case of rnregularization, the regularization parameter was calculated using the same VCE method. Finally, rnthe study area's regional refinement was determined a using geographic grid of 0.5° ��0.5° at searnlevel in Ethiopia. In terms of gravity anomaly and geoid height, the regional solution improves thernGlobal gravity reference field in root mean square (������) from 5.95�������� to 4.33�������� andrn52.90���� to 46.13���� respectively.

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