First image from Sentinel-6B extends sea-level legacy

Following its launch on 17 November 2025, the first data from Sentinel-6B was captured on 26 November by the satellite’s Poseidon-4 altimeter. The image, shown below, is a combination of altimeter data from both the Sentinel-6 sea-level tracking satellites: Sentinel-6B and its twin, Sentinel-6 Michael Freilich, which was launched in 2020. The image shows the Gulf Stream current in the North Atlantic Ocean, off the eastern coasts of the US and Canada.

The Gulf Stream is a hugely important area of the North Atlantic Ocean, not only for the role it plays in global weather patterns and climate, but also because it’s a busy shipping route as well as a key ecosystem for marine species and therefore an important fishing zone.

ESA’s Project Manager for Sentinel-6, Pierrik Vuilleumier, acknowledged the teams’ efforts, “This is the second launch for the Sentinel-6 mission and I am very pleased to see that industry and agency teams have managed again to guarantee the essential continuity of the mean sea-level record, adding five years to the 35 years already accumulated.”

State-of-the-art altimetry

The image was created using data from the mission’s Poseidon-4 dual-frequency (C- and Ku-band) radar altimeter, which uses an innovative mode that has improved performance and resolution compared to previous satellite altimeter designs. Radar altimeter instruments measure the time it takes for radar pulses to reach Earth’s surface and bounce back to the satellite. Sentinel-6 also carries a microwave radiometer, which estimates the delay to the radar pulses caused by Earth’s atmosphere. Both these instruments work together to enable very precise measurements of the sea-surface height as well as wave height and wind speed.

Sentinel-6 also provides data for operational ocean forecasting by providing near real-time data on extreme weather at sea. The mission provides data to support safer navigation at sea, better coastal protection and smarter water-resource management.

ESA’s Director of Earth Observation Programmes, Simonetta Cheli, said, “Developing missions that can track sea-level rise with such precision and long-term reliability is fully aligned with ESA’s core values and strategic goals. The agency’s Earth Observation programmes are focused on providing environments that nurture the innovative technology for such satellites. We also establish the crucial collaborations that enable these missions to become key sources of actionable data for the science community and for climate policy. I thank our European partners as well as NASA and NOAA, and I look forward to seeing this mission continue the legacy of reference data on ocean conditions.”

ESA’s Mission Scientist for the Sentinel-6 mission, Alejandro Egido, said, “It is very encouraging to see Sentinel-6B performing so well soon after launch. While the instruments will undergo a careful calibration phase over the coming months, the quality of the initial dataset is very promising. Once this phase is completed, the mission will be fully prepared to extend the sea-surface height measurement record through at least 2030.”

Continuing the legacy of sea-level data

The Copernicus Sentinel-6 mission serves as the reference mission for satellite altimetry, providing the sea-surface height measurements that underpin the monitoring of sea-level rise, a key indicator of climate change. With sea-level rise high on the global agenda, numerous organisations have worked to make Copernicus Sentinel-6 the gold-standard reference mission for extending the record of sea-surface height measurements – delivering data with greater precision than ever before.

As part of the European Union’s family of Copernicus missions, Sentinel-6 is the product of exceptional international cooperation, involving the European Commission, ESA, NASA, Eumetsat and NOAA, with additional support from the French space agency CNES.