A Study of Movement of Igs Stations Due to Effect of Hydrological Water Loading Using Gps And Grace Data (A Case Study of East Africa)

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Addis Ababa University


This thesis studies the movement of GPS (IGS) stations due to elastic surface deformation of the earth caused by hydrological water loading as detected by the combined monthly Gravity Recovery and Climate Experiment (GRACE) and GPS data for a period of five years from June 2008 to March 2012. The GRACE data was obtained from four different data processing institutes which are Geoforschungszentrum (GFZ) Potsdam, Centre for Space Research (CSR) Texas, NASA Jet propulsion Laboratory (JPL) and Centre National d’Etudes Spatiales (CNES) to estimate total water storage anomalies over the whole of East African region as a case study involving Tanzania, Kenya, Uganda, Rwanda, Burundi and Ethiopia. Five IGS stations were used in this study in addition to six stabilization IGS sites in order to strengthen the network and get improved deformation estimates. Using 650 km half radius Gaussian smoothing, GRACE detected about 5 mm to 17 mm peak-to-peak of total water storage signal with maximum of 7.3 mm in May 2010 and minimum of ~ -17 mm in July 2011 with 2.88 cm mean standard deviation from the mean of the four standard deviations of the four GRACE data models. The derived water load estimates from GRACE were compared with 3D deformation estimates from GPS observations and found good agreement in areas with high and low hydrological signals at every GPS point with maximum correlation of 0.8 for horizontal and vertical components shown by MAL2 and RCMN stations considering enough data between the two signals being correlated. The monthly station positions were obtained with good repeatability computed as weighted root mean square of ~0 mm to 4 mm for horizontal component and ~3 mm to ~10 mm for vertical component. NKLG showed the largest repeatability of 4.6 mm and 18.4 mm for east component and vertical component respectively. The annual GPS signal for north and east components ranged from 1 mm to 4 mm and ~5 mm to ~9 mm for vertical component. However, ADIS and MBAR stations showed strong negative correlation with GRACE signal in north components while RCMN and MAL2 showed strong negative correlations in east components compared with other IGS stations. The analysis of the combined results revealed strong coincidence between GRACE and GPS signal on water loading effect to all studied IGS stations in the study area. The agreement was also observed when GARCE monthly solution signal from this study were compared with precipitation, rainfall and river water discharge from previous studies. Key words: GRACE, GPS, hydrological water loading, IGS station movements



GRACE ;GPS; hydrological water loading ;IGS station movements