Damaged Area Mapping and Ground Displacement Estimation using Sentinel-1 Synthetic Aperture Radar (SAR) Interferometry: January 12, 2020, Taal Volcano Eruption Case Study, Philippines

Abstract

The availability of damage assessment maps and ground displacement information is essential in the Philippines, which experiences various types of climate-induced and naturally-driven geohazards. The emergence of freely accessible space-borne synthetic aperture radar (SAR) data has led to interferometric SAR (InSAR) applications in the Philippines. However, most InSAR studies only focused on ground displacement detection, monitoring, and modeling and not on damages resulting from geohazards. This work used pre- and co-eruption Sentinel-1 interferometric pair datasets and the SeNtinel-1 Application Platform tool to create a pixel-based damage proxy map (DPM) for the 2020 Taal Volcano eruption in the Philippines, employing a coherence difference analysis. The pre-eruption coherence difference data stack mean and standard deviation were exploited to achieve a coherence difference threshold that reasonably created the DPM that delineated damaged areas, which included buildings and roads. The DPM was qualitatively evaluated through comparison with the field investigation and reports obtained from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and showed significant agreement with 89% overall accuracy. The decomposition of the line-of-sight displacement field map revealed the dynamic geological activities due to the phreatomagmatic eruption. The vertical displacements from InSAR and in-situ measurements obtained from field inspection and PHIVOLCS reports showed excellent agreement with root-mean-squared less than 2 cm and coefficient of determination (R2) close to unity. Overall, the application of InSAR to Sentinel-1 SAR images successfully mapped damaged areas and estimated ground displacements associated with the Taal Volcano phreatomagmatic eruption on January 12, 2020.