What Is Ice Thickness?

Ice thickness is a measure of the vertical extent of a body of ice, from its upper surface to its lower boundary with water or bedrock. As a geophysical parameter, it is fundamental to calculating ice volume, estimating freshwater storage, assessing sea-level rise potential, and characterizing ice mechanical behavior. Ice thickness varies across sea ice, glaciers, and ice sheets by several orders of magnitude: Arctic first-year sea ice typically reaches one to two meters, while the East Antarctic Ice Sheet attains depths exceeding four kilometers. Monitoring thickness changes over time is one of the central challenges of cryospheric science.

Because ice covers millions of square kilometers of the polar regions, no single measurement technique can provide complete, continuous coverage. Scientists combine surface surveys, submarine sonar, airborne radar, and satellite altimetry to produce thickness estimates at the scales required for climate research and operational forecasting.

Measurement Methods

The principal techniques for measuring ice thickness reflect the distinct environments involved. For sea ice, upward-looking sonar mounted on submarines has provided observations since the late 1950s: a sound pulse travels through the water column, reflects off the underside of the ice, and the return travel time determines the draft, which is converted to total thickness using density assumptions. Electromagnetic induction sensors towed across sea ice surfaces measure the conductivity contrast between ice and seawater to estimate thickness at local scales. For glaciers and ice sheets, radio echo sounding is the standard airborne method: a radar pulse from an aircraft penetrates through ice and reflects off the basal interface, with the two-way travel time yielding thickness once the wave speed in ice is known. The University of Kansas CReSIS program developed ultra-wideband radar systems capable of mapping ice thickness with centimeter-scale range resolution from long-endurance aircraft.

Satellite Altimetry

Satellite observations transformed the spatial and temporal scope of ice thickness monitoring. Radar and laser altimeters measure surface elevation; when combined with assumptions about hydrostatic equilibrium and ice and snow density, freeboard observations yield thickness estimates over sea ice. ESA's CryoSat-2, carrying a radar altimeter, and NASA's ICESat-2, carrying a photon-counting laser altimeter, have provided high-resolution elevation data over both sea ice and ice sheets since 2010 and 2018, respectively. As the National Snow and Ice Data Center explains, these satellites observe the same location infrequently and face challenges during melt seasons when surface meltwater interferes with radar returns, so satellite data are routinely combined with models and in-situ measurements to produce consistent thickness records.

Ice Sheet Basal Topography

For the major ice sheets of Antarctica and Greenland, thickness data are combined with surface elevation data to map bedrock topography beneath the ice. This subglacial terrain, revealed through decades of airborne radio echo sounding campaigns, determines where ice streams form, where the ice bed lies below sea level (and is thus vulnerable to marine instability), and how grounding lines will migrate as ice thins. The NSIDC and international partners maintain the BEDMAP and BedMachine datasets, which compile thickness measurements from many national programs into continent-wide grids used by ice-sheet models. These grids are essential inputs for projections of ice-sheet contributions to sea-level rise over the coming centuries.

Applications

Ice thickness research has applications in a range of fields, including:

• Sea-level rise projection and ice sheet mass balance assessment
• Arctic shipping and submarine route planning
• Polar climate model initialization and validation
• Subglacial lake and hydrological routing studies
• Structural assessment of ice roads and ice runways in polar logistics