Estimation of geophysical loadings over the malaysian region based on kinematic precise point positioning gps technique

Abstract

The earth’s crust undergoes natural deformation due to the geophysical loadings that consist of the earth body tide, ocean tide loading, atmospheric pressure loading and pole tide. This periodic displacement is generated by the changes of the gravitational attraction between the moon and the sun acting upon the earth’s rotation, along with the temporal atmospheric changes and the variability of the ocean tide. The study of the geophysical loadings is important in the geodesy field as the magnitude of the signals is significant and can contribute to errors in space geodetic measurements such as Global Positioning System (GPS), Very-Long Baseline Interferometry (VLBI) and Altimeter. This study aims to estimate the spatio-temporal variation of the geophysical loadings due to the earth body tide, ocean tide loading and the total signals of the earth tide over the Malaysian region, based on the GPS observations by using a Kinematic Precise Point Positioning (KPPP) GPS approach. Continuous GPS observations over a one-year period in the year 2013 have been utilised to observe the diurnal, semi-diurnal and long-term periods of tidal constituents. The tidal analysis of harmonic and spectral are conducted to examine the characteristic of the geophysical loadings as well as to estimate the tidal parameters of the tidal constituents. The results of the geophysical loadings derived from the KPPP GPS solutions correlate well with the predictions of the theoretical models, IERS2003 and NAO.99b, with the correlation coefficient above 0.90 at three components: north, east and up. The root mean square error (RMSE) is less than ±1 cm at north and east components and around ±6 cm at up component for both earth body tide and earth tide. The RMSE is minimal at all components of ocean tide loading. The presence of the geophysical loadings indicates that as many as 76% to 93% of the geophysical loadings signal are contained in the GPS time series. The findings reveal that earth body tide signals are more significant if compared to ocean tide loading signals because the magnitude of the earth body tide is greater than that of the ocean tide loading and it affects the coordinate system particularly at up component. The spatio-temporal variation of the geophysical loadings is generated during the apogee and perigee phenomena, monsoon seasons and throughout the year 2013 to provide the information on the temporal changes from the geophysical loadings response. Results have widened the understanding of geophysical loadings variations in equatorial regions and illustrated the potential of GPS to provide the local parameters of the geophysical loadings that are beneficial for earth tidal modelling and that can be used to improve the quality of space geodetic measurements.