SENTINEL-1A INSAR MONITORING OF SURFACE DEFORMATION IN DONNELLY TRAINING AREA, ALASKA (2015-2018)

Author

SHISHIR MANANDHAR, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2019

Degree Name

Master of Science

Department

Geography and Environmental Resources

First Advisor

Wang, Guangxing

Abstract

The majority of high-latitude Arctic land surface is underlain by permafrost. The high degree of permafrost sensitivity from climatic as well as anthropogenic factors leads to surface deformation and changing active layer. This is typically due to thawing in warmer seasons and refreezing in colder seasons. Such changes can have significant impacts on the infrastructure and hydroecological environment. Hence, the objectives of this study aimed at identifying spatial pattern and magnitude of surface deformation (uplifting and subsidence) from 2015 to 2018 using Sentinel-1A images in an army installation – Donnelly Training Area (DTA), Alaska. To achieve the objectives, Interferometric Synthetic Aperture Radar (InSAR) method was applied to 11 descending Level-1 Single Look Complex (SLC) images in thawing seasons, spanning from 8th May 2015 to 25th September 2018 with perpendicular baseline up to ±90 m. A Digital Elevation Model (DEM) of 30 m spatial resolution was employed to remove the phase contributed by altitude, to increase the accuracy of differential interferogram and for geocoding. Multilooking, Goldstein phase filtering and phase unwrapping using Minimum Cost Flow (MCF) were conducted on the resulting phase. The unwrapped phase was converted into displacement and it was then terrain-corrected. The collocation of terrain-corrected coherence and displacement was applied followed by the extraction of displacements in the areas where coherence exceeded 0.4 and the displacement was interpolated. Wilcoxon’s signed ranked test was conducted to test if the median displacements were significantly different from zero. The results showed seasonal deformation ranging from -0.43 meter to +0.34 meters. Subsidence was commonly observed between June and July when temperature was high and, uplifting was noticed as a prominent phenomenon after July and before June due to the expansive nature of silty soil and clays. However, the secular changes from May 2015 to May 2018 showed subsidence as a major phenomenon. This could be attributed to the thawing of ice-rich permafrost underneath probably due to global warming and military training activities. Deformations in all pairs were found to be significantly different from zero. These results corroborate with deformation studies conducted in other parts of Alaska and these findings are useful to researchers, decision-makers, and planners of land management.