Identification Of Land Subsidence Rate and Spatial Distribution Pattern Changes Using Envisat ASAR and Sentinel 1, Case Study: Semarang City and Its Surrounding Areas

The area of Semarang City and its surroundings, including the western part of Demak Regency, are experiencing a land subsidence phenomenon, which is caused by combination of a natural factor, (i.e., compaction of unconsolidated alluvial deposits) and anthropogenic factors, especially surface construction loads and excessive groundwater extraction. These anthropogenic factors are responsible for accelerating the rate of land subsidence in the area of Semarang City and its surroundings. Synthetic-Aperture Radar (SAR) imagery could be used to identify land subsidence phenomenon by utilizing interferometry methods such Persistent Scatterer Interferometry Synthetic Aperture Radar (PS-InSAR). This study utilized 16 Envisat ASAR scenes and 20 Sentinel 1 SAR scenes to identify the change of land subsidence spatial distribution pattern and the change of land subsidence rate that occurred in the area of Semarang City and its surroundings using PS-InSAR method between the 2004–2007 and the 2017–2020 periods. The results in the 2004–2007 period showed that land subsidence occurred mostly in the northern part of the study area, where the largest rate of subsidence was observed to occur in the Terboyo industrial area located in the north of Genuk District, reaching 5.3 cm/year. Another large rate of subsidence was also observed to occur in the Tanjung Emas Port area located in the north of Semarang Utara District, reaching 4.7 cm/year. Meanwhile, in the 2017–2020 period, a similar land subsidence spatial distribution pattern was also observed to occur, but in addition, the southern parts of the study area (e.g., southern parts of Pedurungan, Genuk, and Guntur Districts) were also observed to experience subsidence, where previously in the 2004–2007 period there was no land subsidence observed. In general, the rate of land subsidence was also observed to increase significantly in the 2017–2020 period. The largest increase in the land subsidence rate occurred in the most southern part of Genuk District, where the rate of land subsidence was observed to reach 8.4 cm/year in the 2017–2020 period, whereas previously in the 2004–2007 period the subsidence rate was only 2.7 cm/year. This study found that there was land subsidence area expansion, that occurred in the southern part of the study area in the 2017–2020 period and in general, the study area was experiencing an increase in subsidence rate in the 2017–2020 period. © 2025 American Institute of Physics Inc.. All rights reserved.