Comparison between NDVI and InSAR data coherence in deformation analysis caused by the 2022 Pasaman earthquake

Abstract

Abstract One of the destructive earthquakes occurred in Pasaman Barat on February 25, 2022, with a magnitude of 6.1 Mw that caused 27 deaths, 19,221 people evacuated, and an estimated 6,627 houses destroyed. Currently, InSAR is one of the fastest methods to analyze the deformation impacted by an earthquake from processing Sentinel-1 Single Look Complex images. Analyzing the deformation of the 2022 Pasaman Earthquake using InSAR could be challenging because the area consists of high vegetation. It can cause decorrelation due to time difference which increases the possibility of the low coherence value of this data. Excluding the low-coherence result is essential for a better interpretation. This study will analyze the correlation between NDVI and interferogram coherence and eliminate low-coherence data for the displacement deformation map. The NDVI value was calculated using band 4 (Red) and band 5 (NIR) from Landsat 8 images. The InSAR was processed using SNAP, starting from interferogram formation until the conversion phase into displacements, and the map visualization was designed using QGIS. This application of the InSAR method (ascending mode) from Sentinel-1 SAR images can show the deformation, but the coherence level is relatively low. Deformations around the earthquake are shown as uplift and subsidence near the epicenter of the 2022 Pasaman Earthquakes. The high value of vegetation density in the study area causes low coherence between images, so the fringes that identify deformation due to the 2022 Pasaman Earthquake were not seen significantly for the entire study area.