Thirty years after a pioneering satellite duo changed how scientists see ice, the same trick has been pulled off again over Antarctica. By temporarily flying two Copernicus Sentinel-1 radar satellites in close formation, the European Space Agency achieved one-day repeat imaging of the same frozen region. The results map glacier motion and the critical grounding line with precision that was once only possible in the 1990s.
A 1990s breakthrough recreated with modern satellites
ESA’s first Earth observation satellites, ERS-1 and ERS-2, launched in 1991 and 1995. Shortly after ERS-2 reached orbit, ESA maneuvered the pair into a novel tandem formation. For nine months, the two satellites observed the same area of Earth just 24 hours apart. That orbital arrangement gave scientists an unprecedented volume of closely spaced observations and a unique chance to track changes over very short timescales. A later tandem campaign in 2008 paired ERS-2 with the Envisat satellite. Now, the concept has been repeated using the Copernicus Sentinel-1C and Sentinel-1D radar satellites. During Sentinel-1D’s commissioning phase, it was placed temporarily in close formation with Sentinel-1C to achieve a one-day repeat-pass interval. This configuration also allowed cross-calibration of the two satellites and verified their interferometric synthetic aperture radar performance.
What the one-day gap reveals about Antarctica’s ice
The key target of this imaging is the grounding line, the critical boundary where a glacier or ice sheet stops resting on bedrock and begins to float on the ocean, forming an ice shelf. This line acts as an anchor point, controlling how quickly ice flows from the continent into the sea. Both the flow velocity of glaciers and ice streams, and changes in the position of the grounding line, are key indicators of how ice sheets are responding to climate warming. ESA’s Sentinel-1 System Manager, Dirk Geudtner, said the near-simultaneous observations from three Sentinel-1 satellites provided a rare opportunity to monitor glacier and ice-sheet dynamics across different timescales. By imaging the same region of Antarctica just one day apart, the Sentinel-1C and Sentinel-1D satellites recreated the observation time interval that made the original ERS-1–ERS-2 tandem mission a breakthrough for measuring glacier motion and mapping grounding lines.
Why this matters for understanding a changing continent
The ability to measure glacier motion and grounding line position with such precision gives scientists a clearer picture of how Antarctica’s ice is behaving. The tandem approach, first demonstrated three decades ago, remains a powerful tool for observing changes that happen quickly. For researchers studying the frozen continent, these one-day repeat images are rare and valuable data points. They show that even as satellite technology evolves, the simple idea of flying two satellites in close formation can still deliver discoveries about one of the most remote places on Earth.
