Monitoring Based on Differential Radar Interferometry (DInSAR) of the Activity of San Miguel Volcano, El Salvador

The present study demonstrates the application of time series techniques with Differential Interferometry Radar (MT-InSAR) using images from the Sentinel-1 (C-band) and SAOCOM (L-band) radar sensors. The main objective was to identify and assess ground deformation at the San Miguel volcano, one of the most active volcanoes in El Salvador, for study and monitoring purposes. Various approaches were employed to enhance phase signal quality, including the use of Small Baseline Subset (SBAS) and Persistent Scatterers (PS) MT-InSAR methodologies, as well as atmospheric corrections using both the GACOS (Generic Atmospheric Correction Online Service for InSAR) data and an altitude-dependent linear model able to estimate and then remove the stratified component of the troposphere. Additionally, orbital corrections were performed, and the impact of Digital Elevation Model (DEM) accuracy and updates of the topography on phase, especially for SAOCOM L-band images, were evaluated.

The InSAR results revealed subsidence in the volcano crater showing a maximum rate of -25 mm per year, then we modeled the retrieved deformation patterns as a system of normal faults simulating two concentric craters. Moreover, limited deformation was detected in the western upper flank of the volcano during the 2023 period using SAOCOM data. We also observed that the volcano was strongly affected by atmospheric disturbances, although the performed corrections by using GACOS information did not yield to fully satisfactory results. In our work, the importance of using updated and accurate DEMs when processing L-band images has been emphasized.

Finally, our study suggests to continue using SAR images for monitoring San Miguel volcano activity, implementing longer time series with SAOCOM, and performing comparisons between SAR data acquired from both C- and L-band, possibly covering the same period, to gain a more comprehensive understanding of the deformation occurring at San Miguel volcano, and to improve the understanding of the volcanic activity.