Regional Gravity Field Modelling From GRACE Satellite Gravity Mission Data: A Case Study in Ethiopia
| dc.contributor.advisor | Tulu, Besha (PhD) | |
| dc.contributor.author | Samuel, Milki | |
| dc.date.accessioned | 2022-05-13T08:02:54Z | |
| dc.date.accessioned | 2023-11-28T13:46:17Z | |
| dc.date.available | 2022-05-13T08:02:54Z | |
| dc.date.available | 2023-11-28T13:46:17Z | |
| dc.date.issued | 2022-02 | |
| dc.description.abstract | The Gravity Recovery and Climate Experiment (GRACE) mission data-derived gravity field models have provided us with remarkable accuracy in gravity field determination. Despite this, the predicted GRACE baseline accuracy has yet to be met. One reason, among many, could be insufficient satellite data modeling using a global representation by Spherical Harmonics (SH). It appears appropriate to improve global solutions through regional recovery strategies to fully recover the signal information included in satellite and sensor data. Varied geographical regions have different gravity field characteristics, especially in the higher frequency part of the spectrum. As a result, the recovery process should be tailored to the specific characteristics of the area. This regional refinement strategy was employed in Ethiopia. Global gravity reference field, which is represented by SH expansion is then refined using regionally tailored refinements that are specified as space localizing basis functions using splines. The shape coefficients are obtained using the global gravity model's degree error variances truncated up to a maximum degree of 120. This means that the spline kernels must be adjusted to the spectral range of the gravity field features to be calculated. In addition, the raw accelerometer data measured by GRACE Satellites using onboard accelerometers was calibrated. Every short arc over the study area is used, with a 10° strip added to the recovery area. After being synchronized, these short arcs created a partial system of normal equations using an integral equation of the Fredholm type. These normal equations are accumulated to account for varied accuracies of short arcs by estimating variance factors for each arc using variance component estimation (VCE). For only one month of data collected in January 2016, the normal equations are solved using the least squares regularized approach. In the case of regularization, the regularization parameter was calculated using the same VCE method. Finally, the study area's regional refinement was determined a using geographic grid of 0.5° ��0.5° at sea level in Ethiopia. In terms of gravity anomaly and geoid height, the regional solution improves the Global gravity reference field in root mean square (������) from 5.95�������� to 4.33�������� and 52.90���� to 46.13���� respectively. | en_US |
| dc.identifier.uri | http://etd.aau.edu.et/handle/12345678/31647 | |
| dc.language.iso | en_US | en_US |
| dc.publisher | Addis Ababa University | en_US |
| dc.subject | GRACE | en_US |
| dc.subject | Regional Gravity Field Recovery | en_US |
| dc.subject | Space Localizing Basis Functions | en_US |
| dc.subject | VCE | en_US |
| dc.title | Regional Gravity Field Modelling From GRACE Satellite Gravity Mission Data: A Case Study in Ethiopia | en_US |
| dc.type | Thesis | en_US |