Estimating soil moisture in the active layer of the Arctic Foothills using spaceborne InSAR surface deformation data

Abstract:

Recent studies show that groundwater flow through the topmost portion of permafrost soil, known as the active layer, has a significant contribution to the export of carbon in permafrost terrain. As the permafrost continues to degrade, it is becoming increasingly important to characterize the groundwater flow in arctic tundra soil in order to understand how a warming climate will affect soil water content, the thawing of permafrost, hydrological processes, and carbon cycling in permafrost terrain. Because the Arctic covers continent-sized areas that are mostly inaccessible, remote-sensing has become a critical tool for observing the continuous permafrost. Particularly, the density difference between liquid water and ice causes seasonal ground surface deformation that can be detected over large spatial scales using InSAR. Here we analyze L-band ALOS PALSAR data and derived algorithms to extract seasonal and long-term deformation signals caused by thaw subsidence in both fire-disturbed and undisturbed areas. We demonstrate that the magnitude of surface deformation is proportional to the total soil water content by integrating space-borne InSAR deformation data with a large number of soil measurements that contain relevant information on water holding capacity. This allows us to derive an equivalent water depth map over the Toolik area of northern Alaska using InSAR data. We also discovered a strong relationship between the seasonal surface deformation signal, land vegetation cover types, and soil organic carbon content. Our study suggests that InSAR has greater observational capabilities than previously assumed for monitoring changes in hydrological and ecological characteristics above continuous permafrost and for estimating large-scale soil moisture.