Ground Surface Deformation Monitoring of an Active Volcano Using the DInSAR Technique in Comparison with GPS Data: Case Study of Okmok Volcano, Alaska

Mount Okmok is an active volcano, located on the northeastern end of Umnak Island in the Aleutian Islands of Alaska. It is a shield volcano with an approximately 10 km wide caldera, and has undergone several eruptions over the last decades, with the most recent one taking place in 2008. Presence of an underground magma reservoir is manifesting on the surface in form of terrain deformations, e.g. subsidence and uplift. Because of that, Okmok is one of the most thoroughly studied volcanoes in the Aleutian Islands. Its deformations have been examined in the past using field geodetic techniques, like GPS. Work has also been done to determine Okmok's surface displacements using SAR Interferometry. The article presents an approach of calculating terrain deformations with the differential SAR interferometry method, as well as a quality assessment of obtained results by a comparison with GPS data received from various stations located over the study area. The DInSAR calculations have been conducted on a set of radar images taken by the Sentinel-1A and Sentinel-1B satellites from tracks 44, 95 and 117, covering a period of time between years 2015 and 2018. Calculated LOS deformations show that there is a significant uplift in the area of volcano's caldera, in contrast to the rest of Mount Okmok's surface. The comparison with GPS time series shows that both methods bring similar results, meaning that Sentinel-1 imagery processed with the DInSAR method can successfully be used to determine ground surface deformations over large areas.