Preprocessing of Coastal Satellite Altimetry, Tide Gauges, and GNSS Data: Towards the Possibility of Detected Vertical Deformation of South Java Island

AbstractThe Combination of sea surface height (SSH) of satellite altimetry and tide gauge (TG) data with control of GNSS data is proposed as an alternative method of detecting vertical movement of South Java island due to the subduction process. Before the combination, both SSHs have to be preprocessed, especially the satellite altimetry data over coastal area which is noisy due to land contamination signal and fast change of meteorological condition as the location shifts from land to ocean. Preprocessing data was done through retracking waveform altimetry data using two retracking methods. The first processing result of Jason-1 data shows that several complex patterns have occured on the altimetry waveform over the coast of Java Island. It also indicates that the position of the leading edge (PLE) has shifted for about 1.01 - 1.7 from the value of on-board PLE, resulting in the amount of correction of within ± 0.68m. At the same time, the TG data have also been preprocessed to address the gap, spike and change in reference before re-sample following the altimetry sampling time. Using a matlab developed-program, three main problems on TG data could be resolved, and the final TG data has adequate quality for the study. Finally, the GNSS measurement at the tide gauges stations have been processed using GAMIT software to compute the velocity of the crustal movement in 3D, as the control of the proposed-method. Based on statistical testing, it is identified that there is a significant difference in all 3D components of four stations with velocity of 2 – 5cm/year except for Tanjung Mas station, city of Semarang, that has been experiecning rapid land subsidence