Scientists map what lies beneath Antarctica by combining radar measurements of the ice-bed boundary, satellite observations of changes on the ice surface, and models that infer terrain from how ice flows over it. Satellites do not photograph lakes through kilometers of ice: they detect surface changes linked to water below. Each method reveals a different part of the picture, and the resulting maps remain incomplete where measurements are sparse.
How do scientists see beneath Antarctic ice?
No single instrument produces a complete map of Antarctica’s hidden landscape. Researchers combine three kinds of evidence: direct geophysical measurements along survey paths, repeated satellite measurements of the ice surface, and physics-based estimates of terrain between observations.
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| Method | What it measures | What it can reveal |
|---|---|---|
| Ice-penetrating radar | Reflections from layers within the ice and from the bed | Ice thickness, bed shape, and evidence consistent with basal water |
| Satellite altimetry | Ice-surface height over time | Surface deformation associated with filling or draining subglacial lakes |
| Ice-flow inversion | Surface patterns interpreted using ice-flow physics and thickness data | Inferred terrain between geophysical survey observations, at resolvable scales |
The distinction matters: a radar return is a measurement along a survey line; a lake boundary inferred from surface motion or terrain reconstructed from ice flow is an interpretation of measurements.
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How does radar detect subglacial lakes?
Radio-echo sounding sends radio pulses through the ice and records the echoes that return from internal layers and the bed. Because water and ice reflect radio waves differently, basal water can produce a strong reflection. A lake’s water-ice boundary may also appear unusually smooth and flat compared with rough bedrock.
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Researchers assess the radar profile and its surrounding context rather than treating one bright echo as a definitive lake map. Carter and coauthors described reflection categories—definite, dim, fuzzy, and indistinct—based on brightness and specularity. These are interpretive classifications of radar returns, not four universally defined kinds of lake.
Radar also measures ice thickness along its path. Combined with surface elevation, thickness helps constrain the bed’s elevation. Airborne and ground-based geophysical surveys provide direct evidence, but their tracks are unevenly distributed. In many regions, the distance between tracks is on the order of 10–100 km, leaving gaps where the bed must be inferred.
Can satellites see through Antarctic ice?
No. Satellite altimeters measure the height of the ice surface, not the lake beneath it. When a subglacial reservoir fills, the ice above it can rise; when water drains away, the surface can subside. Repeat height measurements reveal this deformation and let scientists estimate the footprint and activity of a lake system.
NASA’s 2021 explanation of ICESat-2 describes how precise surface-elevation measurements helped refine lake maps and identify two additional active lakes in West Antarctica. CryoSat-2 radar altimetry has also enabled repeated, broad observations of surface change.
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A 2013 case study by McMillan and colleagues used CryoSat-2 to map the perimeter and depth of a 260 km² surface depression above a subglacial lake. It illustrates how surface topography can help characterize a lake, but it does not mean the satellite directly imaged the water body.
What did CryoSat-2 reveal about active lakes?
In a study published in Nature Communications on 19 September 2025, Wilson and colleagues analyzed a decade of swath-processed CryoSat-2 data and identified 85 active Antarctic subglacial lakes. The study said this increased the then-known active-lake count by 58%. Those figures describe that study’s data, period, and definition of activity—not a timeless census of every lake beneath the continent.
During the study period, the researchers documented 37 complete drainage events and 34 complete filling events, as well as five lake networks in which upstream drainage occurred alongside downstream filling. Other monitoring approaches have different limitations: visible-wavelength laser altimetry can have cloud and repeat-track gaps, while radar interferometry depends on coverage and coherence between image pairs.
Active lakes matter because water moving at the base of the ice can change pressure and friction, potentially affecting ice motion. The overall influence of subglacial lake activity on Antarctic ice speed remains undetermined; drainage should not be assumed to make an ice stream move faster in every case.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do scientists map terrain between survey lines?
Ice flowing over bedrock highs and valleys develops stress patterns that can produce corresponding variations in the ice surface. Ice-flow physics can be applied to high-resolution surface observations to infer which subglacial topography could have generated those patterns. This broadens mapping beyond the narrow paths covered by direct geophysical surveys, but the terrain is inferred rather than directly measured everywhere.
In a paper published in Science on 15 January 2026, Ockenden and colleagues presented a continental-scale elevation map combining satellite surface observations, geophysical ice-thickness measurements, and corrections that align the inferred result with available geophysical observations. The method targets mesoscale landforms roughly 2–30 km across. Its authors say it cannot resolve features shorter than the ice thickness, because those features do not create a detectable surface perturbation.
The map reveals or sharpens features including incised valleys, channels, highlands, and linear boundaries that may have geological or tectonic origins. One example in Maud Subglacial Basin is a channel averaging 50 m deep, about 6 km wide, and nearly 400 km long. The authors hypothesize that it may be linked to drainage from the Dronning Maud Land mountains; it is a mapped feature and proposed interpretation, not a directly observed open river beneath the ice.
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Each measurement answers a different question. Radar helps establish what the bed looks like along a flight or ground track and can identify reflections consistent with water. Satellite altimetry tracks surface changes that reveal lake activity over time. Thickness data help constrain the distance between surface and bed, while ice-flow inversion uses the surface response to extend terrain interpretation between measurements. Gravity and magnetic data can add clues about broader geological structure.
- For direct evidence of basal water or bed shape: radar and other geophysical surveys are central, but their detail is limited to surveyed paths and surrounding coverage.
- For changing lake activity: repeated altimetry shows how the surface rises or falls over time, rather than seeing through the ice.
- For broader terrain coverage: physics-based mapping can identify mesoscale features between observations, but not features below its resolution limit.
Survey spacing, surface-signal limitations, and incomplete understanding of lake filling and drainage all leave uncertainty. A lake inventory or terrain reconstruction is therefore a map of the evidence available to a particular study, not a final account of everything under Antarctica.
Quick Recap
Sources
- Wilson et al., “Detection of 85 new active subglacial lakes in Antarctica from a decade of CryoSat-2 data,” Nature Communications, 2025
- NASA Goddard, “NASA Space Lasers Map Meltwater Lakes in Antarctica With Striking Precision,” 2021
- Ockenden et al., “Complex mesoscale landscapes beneath Antarctica mapped from space,” Science, 2026
- Carter et al., “Radar-based subglacial lake classification in Antarctica,” Geochemistry, Geophysics, Geosystems, 2007
- McMillan et al., “Three-dimensional mapping by CryoSat 2 of subglacial lake volumes,” Geophysical Research Letters, 2013
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