Estimation of Spouted Hot Mudflow Current Using Continuity Equation and DInSAR

Several techniques have been proposed to observe long-term land surface deformation using phase information of synthetic aperture radar (SAR), for example, interferometric SAR (InSAR), differential interferometric SAR (DInSAR), permanent scatterer interferometric SAR (PS-InSAR), and small baseline subset (SBAS) using images of JERS-1, ALOS-1/2, ENVISAT, ERS-1/2, RADARSAT-1/2, TerraSAR-X, SENTINEL-1A/B, and so on. These methods have also been employed to investigate land deformation and the impact caused by the hot mudflow accident at the study area of regency of Sidoarjo, East Java province, Indonesia, where this disaster happened on May 29, 2006, and has been flowing until now. But these methods only derived the land surface deformation and did not figure geological situation in the Earth, especially the current of geological material outflow. Therefore, this research proposed the continuity equation of the law of conservation of material to estimate the current of material outflow to investigate the impact of the land surface disaster in the study area. The information of vertical deformation or subsidence is derived by the consecutive DInSAR using multispaceborne SAR and substituted into the proposed equation to estimate the volume and current of hot mud outflow. The differential global positioning system (GPS) data collected since 2006 were employed to validate the analysis result of land surface deformation, and the root means square (rms) error is 0.46 m. The result obtained the current at the center of the study area at the beginning of the mudflow period was 6800 m3/day and decreased from 2018 until now that matched well with the local reports. The proposed equation could also be applied for observation of land deformation, volcano, fault activity, underground water, and so on, using remote sensing technologies.