Quantifying Surface-Height Change Over a Periglacial Environment With ICESat-2 Laser Altimetry

We use Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) laser altimetry crossovers and repeat tracks collected over the North Slope of Alaska to estimate ground surface-height change due to the seasonal freezing and thawing of the active layer. We compare these measurements to a time series of surface deformation from Sentinel-1 interferometric synthetic aperture radar (InSAR) and demonstrate agreement between these independent observations of surface deformation at broad spatial scales. We observe a relationship between ICESat-2-derived surface subsidence/uplift and changes in normalized accumulated degree days, which is consistent with the thermodynamically driven seasonal freezing and thawing of the active layer. Integrating ICESat-2 crossover estimates of surface-height change yields an annual time series of surface-height change that is sensitive to changes in snow cover during spring and thawing of the active layer throughout spring and summer. Furthermore, this time series exhibits temporal correlation with independent reanalysis datasets of temperature and snow cover, as well as an InSAR-derived time series. ICESat-2-derived surface-height change estimates can be significantly affected by short length-scale topographic gradients and changes in snow cover and snow depth. We discuss optimal strategies of post-processing ICESat-2 data for permafrost applications, as well as the future potential of joint ICESat-2 and InSAR investigations of permafrost surface-dynamics. Plain Language Summary NASA's Ice, Cloud, and Land Elevation Satellite 2 (ICESat-2) was designed to accurately measure surface heights in order to study changes to Earth's ice sheets, sea ice, and biomass. In this paper, we analyze changes in estimated surface-height from ICESat-2 data collected over an area in the Alaskan Arctic, where seasonal freezing and thawing of the ground causes the Earth's surface to deform with time. We compare these estimates of surface-height change with independent estimates of surface deformation acquired by the European Space Agency's Sentinel-1 spacecraft, which was specifically designed to precisely measure surface deformation. By comparing changes in estimated surface height from the ICESat-2 mission to surface deformation measurements from Sentinel-1, we demonstrate agreement of the estimated spatial patterns of surface deformation, suggesting that ICESat-2 data can be used to quantify surface dynamics in tundras. Further, the different strengths of ICESat-2 laser altimetry and Sentinel-1 interferometric synthetic aperture radar (InSAR) could be jointly leveraged to provide novel insights into periglacial surface processes. We discuss several phenomena that can complicate ICESat-2 surface-height change estimation and introduce errors, as well as future methods that might be employed to mitigate such errors.