PSInSAR Processing for Volcanic Ground Deformation Monitoring over Fogo Island

Persistent Scatterer SAR interferometry (PsInSAR) has been widely used in the precise measurement of ground deformation due to anthropogenic and natural disturbance of the Earth's surface. The present study has utilized the spaceborne C-band Sentinel-1 data for PsInSAR processing to generate a displacement map due to the volcanic eruption of Pico do Fogo volcano of the Fogo Island. An eruption was recorded in the year 2014-15 and the Fogo volcano became active on November 23, 2014. It was observed that the intensity of volcanic eruption during 2014-15 had approached the intensity of the volcanic eruption of 1951 which was recorded as one of the strongest eruptions on the island. The volcanic eruption continued for 77 days and it stopped on February 8, 2015. To find the mean line of sight displacement from PsInSAR processing, a total of 7 SLC products of Sentinel-1 data in the interferometric mode was used. The SLC product of the SAR data which was acquired before starting the volcanic eruption was chosen as the master image and all the remaining 6 slave images were precisely coregistered. Selection of persistent scatterers (PS) is the most important step in PsInSAR processing. The initial set of PS was identified by amplitude stability index and the phase analysis was performed to estimate the phase stability of each resolution cell. After PS identification, 3D phase unwrapping was performed. The unwrapping step involved the low-pass filtering of the complex phase difference and time series in the frequency domain using a Gaussian window. The phase difference between each filtered data point is then calculated. The unwrapped phase of the interferogram was used to generate a displacement map for the volcanic field. The PsInSAR based line of sight displacement was measured in the range of -34 mm to +35 mm and the standard deviation of the displacement was ranging from +2 mm to +30 mm.