InSAR measurements of surface deformation over permafrost on the North Slope of Alaska

Ground-based measurements of active layer thickness provide useful data for validating/calibrating remote sensing and modeling results. However, these in situ measurements are usually site-specific with limited spatial coverage. Here we apply interferometric synthetic aperture radar (InSAR) to measure surface deformation over permafrost on the North Slope of Alaska during the 1992-2000 thawing seasons. We find significantly systematic differences in surface deformation between floodplain areas and the tundra-covered areas away from the rivers. Using floodplain areas as the reference for InSAR's relative deformation measurements, we find seasonally varying vertical displacements of 1-4 cm with subsidence occurring during the thawing season and a secular subsidence of 1-4 cm/decade. We hypothesize that the seasonal subsidence is caused by thaw settlement of the active layer and that the secular subsidence is probably due to thawing of ice-rich permafrost near the permafrost table. These mechanisms could explain why in situ measurements on Alaskan North Slope reveal negligible trends in active layer thickness during the 1990s, despite the fact that atmospheric and permafrost temperatures in this region increased during that time. This study demonstrates that surface deformation measurements from InSAR are complementary to more traditional in situ measurements of active layer thickness, and can provide new insights into the dynamics of permafrost systems and changes in permafrost conditions.