Synthetic Aperture Radar (SAR) for Measurement of Permafrost Behavior on the North Slope of Alaska. A Tool for Ground Displacement Assessment Throughout Project and Infrastructure Lifecycles.
Authors: Lucente Courtney , Falorni Giacomo , Tortini Riccardo 
Published: May 2023

The North Slope of Alaska is a prolific hydrocarbon producing area, currently estimated to be the largest oil field in the United States and contains one of the greatest reserve accumulations.

The North Slope is a tundra covered region including the majority of the northern portion of the state of Alaska that is underlain by an extensive and continuous permafrost layer (Jorgenson, et al., 2008). To support the vast oil and gas development on the North Slope, significant infrastructure, including well pads, facilities, air strips and pipelines/flowlines, has been constructed over the past few decades. All this infrastructure is in some way in contact with the underlying permafrost. The Alaska Department of Transportation and Public facilities has identified two primary ways through which permafrost changes can damage infrastructure. The first is through differential settlement, caused by thawing; the second is seasonal freeze-thaw cycles (Alaska Department of Transportation and Public Facilities, 2022). Both phenomena are present on the North Slope to varying degrees at varying locations.

It is widely accepted that, globally, permafrost is warming and, in many cases, thawing (Runge, Nitze, & Grosse, 2022). Some studies estimate natural hazards and the risk of transportation infrastructure loss due to permafrost changes could reach 20% by the year 2030 (Tromifenko, Evgenev, & Shashina, 2017). Tromifenko et al. (2017) underline the necessity to develop climate change indicators to assess the risk to infrastructure in permafrost areas. They highlight the importance of utilizing this data during the design, construction, and operation of northern arctic infrastructure. Interferometric Synthetic Aperture Radar (InSAR) represents a powerful tool through which to assess long and short-term changes to the permafrost over extensive and remote areas.

Here we will show a case study from the North Slope of Alaska. InSAR data collected and processed over the site highlights the magnitude, seasonality, and location of permafrost changes. This analysis includes developed and undeveloped areas, in different stages of the development cycle. The high temporal and spatial coverage of the InSAR point cloud allows for comparison of settlement behavior between individual pieces of infrastructure compared to their immediate surroundings. In undeveloped areas, the displacement data allows to identify the areas with the largest subsidence rates, as well as the greatest degree of seasonal freeze-thaw displacement.

InSAR is a satellite based remote sensing technique for assessing ground deformation. By obtaining millimetric precision and high spatial and temporal density, it provides valuable insights to augment and enhance traditional survey techniques such as GPS.

In addition to the InSAR analysis, this study also leverages the amplitude component of SAR data to analyze water body ice dynamics using a novel quantitative approach. The results of this analysis provide insights into spring break up on the rivers which transect many of the oil and gas fields in the region.