ATMOSPHERICALLY CORRECTED D-INSAR TO DETECT TIME SERIES DEFORMATION AT AGUNG VOLCANO USING SENTINEL-1A SAR DATA

摘要

Agung volcano located in the far east of Bali Island. Indonesia is one of the active volcanoes parts of Circum-Pacific ring of fire. Following the large eruption of 1963, the seismicity of Agung volcano increased significantly and put into alert level IV in September 22nd, 2017. Then, the early eruptions had occurred in November 25th and 26,h. 2017. Regarding the eruptions, this research was aimed to observe the deformation series of Agung volcano from August 2017 to January 2018 using the atmospherically corrected Differential Interferometric Synthetic Aperture Radar (D-InSAR) of multiplatform Sentinel-IA data. The D-InSAR techniques were commonly used for surface deformation monitoring by eliminating the topographical influence of the interferogram's phase. The Pairwise Logic Technique as termed as PLT was applied following the D-InSAR processing to eliminate atmospheric phase delay. The common image selection for D-InSAR pair served as the basis of the PLT. The method was adopted to Sentinel-IA data in ascending and descending orbits to observe the deformation change in Line-of-Sight (LOS). The deformation velocity was then calculated on the daily basis to omit the variation of temporal baseline. According to the PLT in ascending orbit, the surface velocity near the summit was calculated from -4.1 mm/day to 2.9 mm/day. The velocity obtained from the descending orbits was slightly different than the ascending orbit, from -2.5 mm/day to 3.6 mm/day due to different LOS orientation and time reference of the data. The deformation patterns formed from the deformation magnitude showed that the inflation occurred near the time of the eruption and the subsidence followed the eruption due to changes of pressure in the reservoir.