Vertical land motion estimation derived from space-based geodetic techniques

Abstract

Vertical land motion is associated with land geohazards that portrays land movement in subsidence and uplift. As Malaysia is exposed to the tropical climate, heavy rain will cause the floodwater to submerge land or coastal areas, particularly in the presence of land subsidence. This could result in severe environmental consequences, such as inundation and economic losses. Therefore, this study presents an approach to estimate the rate of vertical land motion using multi-sensor technology, which are the Global Positioning System (GPS), Gravity Recovery and Climate Experiment (GRACE), and integrating them with the satellite altimeter minus tide gauge techniques. The four objectives of this study were to improve the accuracy of the vertical component on GPS measurement by mitigating the effects of seasonal variations, to derive the deformation of the Earth surface induced by hydrological loading and tectonic motion on GRACE measurement, to quantify the coastal vertical land motion using satellite altimeter minus tide gauge technique, and to integrate the vertical land motion rates within a 19-year period, from 1999 to 2017, for the region of Malaysia using space-based geodetic techniques. The methodology used was to firstly generate GPS vertical position time series from Bernese 5.2 software by considering the diverse geophysical sources on seasonal variations. Then, the vertical displacement of the Earth’s surface was derived from the GRACE measurement. This was followed by the quantification of coastal vertical land motion using direct and advanced approaches. Finally, the rate of vertical land motion was then derived from each multi-sensor space-based geodetic technique before it was integrated using the least-squares collocation method over the Malaysian region. As Malaysia experiences land subsidence and uplift based on the integrated vertical land motion rates, as such the analysis of vertical land motion trend produced novel findings. The absolute motions indicated an overall displacement from a subsidence rate of -20 mm/yr. to an uplift of 5 mm/yr. A significant subsidence rate was observed at specific areas in Peninsular Malaysia due to groundwater extraction and natural compaction, except for Pantai Tok Jembal, which experienced coastal erosion. In East Malaysia, other areas encountered land subsidence due to peatlands, excluded Kota Belud and Kota Marudu as the groundwater development project had taken place at these areas, which gave proof of the dominant effect of land subsidence in Malaysia. In conclusion, the integration of multi-sensor technology in quantifying vertical land motion rates would not only help researchers obtain insight into the motion trends, but it also serves as a key to forecast the necessities of populations and environment, thus implementing appropriate monitoring and prevention measures for future geohazard risk assessment.