Land Subsidence Monitoring in Semarang (Indonesia) by SBAS-DInSAR using ALOS-2 and Sentinel-1 SAR data from 2015 to 2023

Land subsidence in Semarang is a famous environmental problem in Indonesia. This Subsidence was monitored by GPS ground surveys from 2008 to 2016 and Interferometric Synthetic Aperture Radar (InSAR) by other researchers. In this study, the SBAS-DInSAR is applied to monitor Subsidence in Semarang using ALOS-2 and Sentinel-1 SAR data. Both SAR datasets, ALOS-2 and Sentinel-1, are almost in the same observation period (2015 to 2023). This study presents the first application of SBAS-DInSAR using the ALOS-2 dataset. The updated Subsidence in Semarang City obtained by SBAS-DInSAR using ALOS-2 and Sentinel-1 is presented. The SAR dataset, ALOS-2, and Sentinel-1 show that the maximum accumulated Subsidence over eight years (from 2015 to 2023) is about 90-100 cm with an average subsidence velocity of about 11-12.5 cm/year. The subsidence area is mainly located in the north and northeast areas. The subsidence results obtained by ALOS-2 and Sentinel-1 coincide from spatial distribution and temporal transition points of view. The discrepancy between ALOS-2 and Sentinel-1 is less than 1 cm on average.