Introduction
On November 16, 2025, the Sentinel-6B satellite launched from Vandenberg Space Force Base (VSFB) in California. The mission is a partnership between NASA, the National Oceanic and Atmospheric Administration (NOAA), and several European partners – the European Space Agency (ESA), the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), the French Centre National d’Études Spatiales (CNES), and the European Commission. Its objective is to continue collecting data to extend the ocean height record, which was started in 1992 with the U.S./French TOPEX/Poseidon satellite mission. During the past three decades, NASA and its partners have operated a satellite in the same orbit, precisely tracking the height of the oceans across the globe, once every 10 days.
Sentinel-6B took to the skies almost five years to the day after its twin, Sentinel-6A, which launched November 20, 2020, also from VSFB, and was renamed Sentinel–6 Michael Freilich, honoring the former head of NASA’s Earth Science Division – see The Editor’s Corner [March–April 2020, 32:1, 1–2]. Together, the two missions comprise the international Sentinel-6/Jason – Continuity of Service (CS) mission, which will provide continuity with past missions from TOPEX/Poseidon through Jason-3. Sentinel-6B will continue to measure sea level to about one inch (2.5 cm), extend the record of atmospheric temperatures, and continue sea level observations through the end of the 2020s.
The article that follows briefly introduces Sentinel-6B’s payload (which is the same as Sentinel–6 Michael Freilich). It then describes the planned science applications of the mission, followed by a brief conclusion.
Sentinel-6B Payload
The Sentinel-6B satellite carries several instruments to support the mission’s science goals – see Figure 1. A Radar Altimeter bounces signals off the ocean surface to determine the distance to the ocean. An Advanced Microwave Radiometer (AMR) retrieves the amount of water vapor between the satellite and ocean, which affects the travel speed of radar pulses, providing a critical correction to the distance measured by the radar. Other onboard instruments are used to precisely determine the satellite’s position [e.g., Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) and Laser Retroreflector Array]. The height of the ocean surface can be calculated by combining the satellite’s position with the distance to the ocean. In addition, S- and X-band antennas perform data downlinks, and a solar array supplies power.
Beyond these instruments, Sentinel-6B contains Global Navigation Satellite System Radio Occultation (GNSS-RO) instrument that will aid with weather prediction. Observations made between the spacecraft instrument and other GNSS satellites as they disappear over Earth’s limb, or horizon, will provide detailed information about variations in the layers of the atmosphere. This information will contribute to computer models that predict the weather and enhance forecasting capabilities.
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