GNSS measurement of seasonal ice flow velocity of the northeast Greenland ice stream and Jakobshavn Isbræ, Greenland.

In 2016, we established the first network of GNSS stations on the Northeast Greenland Ice Stream (NEGIS), enabling continuous monitoring of ice flow motion and surface elevation changes. These stations have revealed both short-term variability and longer-term accelerations that propagate far inland from the terminus (Khan 2022; Khan 2024), highlighting the dynamic coupling between the glacier front and the interior of the ice sheet. Building on this effort, in 2024 we deployed four additional GNSS stations on Jakobshavn Isbræ, one of Greenland’s fastest-flowing outlet glaciers. All stations on both Jakobshavn and NEGIS are located along the main glacier trunks, spanning distances of ~20 to ~200 km from the terminus, thereby capturing spatial gradients in flow and deformation.

The GNSS sites also enable direct validation of satellite-derived surface elevation products (ICESat-2 and CryoSat-2). Whereas satellite altimetry provides repeat measurements of ice-surface elevation once per month, GNSS observations deliver continuous, hourly records of both vertical and horizontal ice motion. This high temporal resolution allows us to resolve short-lived dynamic events, seasonal signals, and longer-term trends that are not detectable from spaceborne sensors alone. Together, these complementary datasets provide powerful constraints for improving ice-flow models and for assessing the future evolution and stability of the Greenland Ice Sheet.

In addition, we apply GNSS interferometric reflectometry (GNSS-IR) to the ice-sheet environment, using reflected GNSS signals to infer changes in ice-surface height and physical properties such as roughness and snow accumulation. This technique adds a new observational dimension to the GNSS network, further enhancing its value for characterizing glacier–atmosphere interactions and surface processes.