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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Date
2013-07
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Addis Ababa University
Abstract
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
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Keywords
GRACE ;GPS; hydrological water loading ;IGS station movements