[A-CG46] Science in the Arctic Region

[ACG46-12] InSAR detection of surface displacements associated with permafrost change in Prudhoe Bay, northern Alaska

*Marika Konta¹, Masato Furuya² (1.Graduate School of Science, Hokkaido University, 2.Department of Earth and Planetary sciences Hokkaido University)

Keywords:permafrost, Interferometric Synthetic Aperture Radar, thermokarst

In recent years, the earth has been experiencing climate change due to global warming. Especially arctic earth cryosphere is the area strongly affected by global warming. In the permafrost zone distributed in the Arctic region, a decrease in the freezing period and an increase in the thawing depth have been observed with the progression of global warming. The active layer above the permafrost repeats thawing in summer and refreezing in winter. When ice-rich permafrost areas are strongly affected by global warming, the temperature in summer will rise. Under high temperatures, the ice beneath the active layer will thaw and flow out from the soil. Volume decrease of the soils causes settlement, and makes the ground surface bumpy, called thermokarst. The ground settlement could lead to construction damage or collapse because they are constructed just above the active layer. We focus on the North Slope of Alaska near Prudhoe Bay. This area, a continuous permafrost area, has much of bumpy landforms due to the thaw settlement as described above. The surface displacements are small, a few centimeters per year. However, it is hard to observe this change directly because the displacements could occur where large ice is in the permafrost, and we have to keep a wide range of more than tens of square kilometers. In addition to field observation, image analysis using artificial satellites has attracted attention in recent years to solve this problem. This technology is our research method, Interferometric Synthetic Aperture Radar, called InSAR for short. Artificial satellites shoot the same range on the ground two times. We can generate one interferogram using two satellites' images and detect the surface displacements that occurred during two periods. Using ground-based and InSAR observation enables the quantification of ground surface dynamics and inference of near-surface ground ice content in the North Slope of Alaska near Prudhoe Bay(Liu et al., 2014). In that study, researchers focus on each drained thermokarst lake basins(DTLB) that are ubiquitous landforms on Arctic tundra lowlands. They use only the snow-melting season data, from June to September, between 2006 and 2010 to avoid severe phase decorrelation and artifacts due to snow cover. However, it doesn't snow much in Prudhoe Bay and we have the snow-season data. In our study, we focus on the same place as the previous study and generate interferograms using the snow-season data, from October to May, between 2007 and 2011. Moreover, we could use annual data between 2016 and 2020. As a result of InSAR image analysis, we could generate interferograms using snow-season data and detect the signal of seasonal thaw settlement and frost heave at Sagavanirktok river from the data between 2016 and 2018. The degradation signal was shown in a temperature-rising combination and the uplift signal was shown in a temperature-falling combination. In addition, the amount of displacement was a few centimeters. These points suggest that the signals are related to permafrost seasonal settlement or frost heave. However, there is an issue that we could not eliminate the ionosphere noises.