Land subsidence analysis using DInSAR and GNSS survey in Medan-Belawan City, North Sumatera, Indonesia

Rapid land subsidence is a major threat to coastal megacities in Indonesia. However, spatially detailed information on subsidence rates remains limited in Indonesia, particularly for Medan-Belawan. This study aimed to quantify land subsidence rates in Medan-Belawan and assess the consistency between ground-based and satellite-based measurements. Land subsidence was measured using Global Navigation Satellite System (GNSS) observations at 10 benchmark (BM) points and Differential Interferometric Synthetic Aperture Radar (DInSAR) analysis using Sentinel-1A imagery. Both methods consistently indicated substantial subsidence across the city. GNSS-derived subsidence rates ranged from -0.84 to -8.76 cm/year, while DInSAR-derived rates ranged from -6.18 to -13.56 cm/year. The overall mean subsidence rate was -6.41 cm/year, with an RMSE of 6.57 cm between the two approaches. The highest subsidence rates were concentrated in districts with very high population densities. Medan-Belawan is experiencing significant land subsidence, and GNSS and Sentinel-1A DInSAR provide broadly consistent estimates. The spatial concentration of high subsidence in densely populated districts highlights the need for targeted monitoring and mitigation strategies.