Date of Award
Doctor of Philosophy (PhD)
John M. Wahr
In past decades, cryospheric components such as glaciers, ice sheets, sea ice, and frozen ground have been undergoing significant and rapid changes, associated with changes in the global climate system. In this research, I present two case studies on how geodetic tools, especially Radar Interferometry (InSAR), can be used to monitor and to advance our understanding of the changing cryosphere. First, I measure seasonal and long-term surface subsidence on the North Slope of Alaska near Prudhoe Bay using InSAR. I detect a long-term surface subsidence of 1 to 4 cm per decade, which is probably caused by melting of ground ice within the permafrost, as ground temperatures have increased by 2 to 3°C in northern Alaska since the early 1980s. I also find a seasonal subsidence of 1 to 4 cm during summer thaw seasons, which is caused by the volume decrease of the top soil layer (the active layer) undergoing annual thawing-freezing cycles. A retrieval algorithm is developed to estimate the active layer thickness (ALT) using the InSAR-measured seasonal subsidence. The estimated ALT values match in situ measurements at Circumpolar Active Layer Monitoring sites within the uncertainties. I estimate an ALT of 30 to 50 cm over moist tundra areas, and a larger thickness of 50 to 80 cm over wet tundra areas. Second, I use InSAR and Global Positioning System data to measure the crustal elastic uplift near Jakobshavn Glacier in west-central Greenland caused by its rapid ice loss since 1997. These geodetic measurements place valuable constraints on the ice mass balance estimation based on altimetry measurements from NASA's Airborne Topographic Mapper (ATM), as I find good agreement between the observed crustal rebound rates and the predicted rates using the ATM measurements. I also directly invert for the spatial pattern of ice thinning from the InSAR-measured crustal deformation. Overall, this research suggests that InSAR-measured surface deformation complements traditional in situ monitoring of the active layer and the permafrost, extends ALT estimates over large areas at high spatial resolution, provides new insights into the dynamics of permafrost systems and changes in permafrost conditions, and helps to study the ice mass loss of a rapidly thinning glacier and its surrounding region and to better understand a glacier's rapid response to a warming climate.
Liu, Lin, "Studying Changes in the Cryosphere Using Radar Interferometry: Permafrost Surface Subsidence and Glacial Unloading Deformation" (2011). Physics Graduate Theses & Dissertations. 27.