OBSERVER: With the launch of Sentinel-6B, Europe builds on its ocean monitoring legacy

As November approaches, the EU Space Programme is preparing for its next milestone in Earth Observation (EO): the launch of Copernicus Sentinel-6B, the second of two identical satellites in Europe’s sea-level monitoring mission. Set to launch from Vandenberg Space Force Base in California, the satellite carries a sophisticated radar altimetry instrument capable of measuring sea-surface height with centimetre precision, providing essential data for understanding climate change and protecting coastal communities worldwide. In this Observer, we look at how the Copernicus Sentinel-6 satellite mission continues a thirty-year record of ocean altimetry with the launch of Sentinel-6B, ensuring continuity and precision in what has been an active year of satellite deployments for the EU Space Programme.

Global sea levels continue to rise as Earth's climate changes. Coastal cities in Europe, from Rotterdam to Venice face increased flood risks, while small island nations remain among the most vulnerable to rising seas. Understanding exactly how fast seas are rising, and where, requires precise measurements from space and long time series.

Copernicus Sentinel-6 is the reference satellite mission for sea-surface-height measurements, ensuring continuity of the global ocean topography record which started in 1992. Sentinel-6 Michael Freilich (Sentinel-6A), launched in 2020, flies the long-established reference ground track, with a roughly 10-day repeat cycle, delivering centimetre-level sea-surface-height data together with significant wave height and wind-speed measurements.

Thanks to its state-of-the-art instruments, the satellite mission provides high-accuracy and stable measurements that serve as the benchmark for calibrating other satellite altimetry datasets, underpinning global mean sea level estimates and regional sea-level variability analyses.

The Copernicus Marine Service integrates Sentinel‑6 observations with those from other Copernicus Sentinel satellites and partner missions to produce operational oceanographic products and climate data records, providing downstream analyses and forecasts used by public authorities, industry, and researchers worldwide. Among these are the Global Ocean Along Track Sea Surface Heights data, visualised below, which provides measurements of the ocean’s surface height along the satellite’s ground track. Additionally, Sentinel-6 observations feed into products measuring global wave height and specific Ocean Monitoring Indicators (OMIs) focused on sea level rise.

Scientists use Sentinel-6 observations to monitor the rate of global and regional sea-level rise, map ocean currents, and derive sea-state parameters such as significant wave height, supporting coastal risk assessment, maritime safety, and climate policy applications in Europe and beyond.

Sentinel-6B, scheduled for launch in November 2025, will ensure the continuity of these measurements, maintaining the accuracy and stability of the global sea-level record. With a nominal lifetime of around five and a half years, it will provide users across the world with reliable data through 2030.