D2 Geodesy and Movement in the Field

Topic

Geodetic and field methods directly measure the movement, deformation, and volume change of ice masses by placing instruments on the glacier surface or within the ice itself. These methods complement satellite remote sensing by providing centimeter-level precision at specific points on the glacier—precision that is essential for calibrating and validating the data collected by satellite remote sensing from space.

A differential satellite positioning system determines the location of a mobile receiver moving across the ice by comparing the phase of the signal it captures with that of the same signal received by a fixed reference station; this phase comparison yields a precision of one to two centimeters horizontally and three to five centimeters vertically.

Ablation stakes are rods inserted directly into the glacier ice; as the surrounding ice melts, the stakes become increasingly exposed above the surface, and this progressive emergence directly measures the amount of ice melted at that specific point on the glacier.

Terrestrial laser scanning and photogrammetry using unmanned aerial vehicles (UAVs) each generate a high-resolution, three-dimensional point cloud of the glacier surface; by comparing point clouds captured at different times, both terrestrial laser scanning and UAV-based methods allow for the creation of a digital model showing the exact change in surface elevation between captures. Inclinometers and deformometers installed in boreholes penetrating the glacier ice measure—from within the ice itself—the speed at which the ice slowly deforms under its own weight; this is a type of continuous internal deformation known to glaciologists as "ice creep."

Collectively, these geodetic and field methods reveal an expected glacier velocity profile that peaks at the surface and decreases at an accelerating rate with increasing depth, alongside seasonal ablation rates—measured by ablation stakes—that align with the energy the glacier receives during each season; this confirms the role of these geodetic and field methods in calibrating and validating the satellite remote sensing techniques mentioned earlier.

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