Detection of land subsidence in Semarang, Indonesia, using stable points network (SPN) technique

Land subsidence in Semarang is a severe hazard threatening people and urban infrastructure. The evolution of land subsidence has been monitored between 1996 and 2000 with few leveling stations. Hence, maps show an overall distribution of land subsidence, but are inaccurate in detail. Stable points network (SPN) technique has been applied to improve land-subsidence mapping. SPN measures ground motion using Synthetic Aperture Radar satellite images. For the SPN processing, 35 radar satellite images acquired between 2002 and 2006 have been selected. Derived land-subsidence rates vary from fractions of 1 mm/year to values of 10 cm/year and even beyond. Classification and visualization of the ground motion data illustrate the boundary between mainly stable ground in the south of Semarang and increasingly land-subsidence-affected land toward the coast. Final result is a map featuring the land subsidence with much higher accuracy as had been possible before. This article presents a brief description of the land subsidence in Semarang and introduces briefly the concept of SPN technique. Results of SPN-based ground motion detection in Semarang are presented and discussed from a user's point of view.