Program for Arctic Regional Climate Assessment (PARCA) is a NASA-funded initiative directed toward an improved understanding of the mass balance of the Greenland Ice Sheet.
PARCA involves several approaches to measuring ice sheet mass balance, including spaceborne and airborne altimetry as well as ground-based programs.
One approach is to calculate local rates of ice sheet thickness change using precision GPS methods (the so-called "coffee-can" technique). This technique entails comparison of ice vertical velocities, obtained from GPS, with long-term rates of snow accumulation, derived from ice core stratigraphy. Small adjustments must be made to account for the effects of along-slope flow and firn compaction. Calculated rates of thickness change apply to geophysical-length timescales (100-1000s years, the length of the ice core record) and have small uncertainties.