"These first observations already illustrate the value that Sentinel-6B will add as the next world’s reference mission for high-precision satellite altimetry well into the 2030s. Our teams, together with our European and US partners, are now entering the critical phase of calibration and validation to ensure we deliver the trusted data that scientists, forecasters and communities rely on to better understand and protect our oceans," said EUMETSAT Director-General Phil Evans.

Christoph Kautz, Director for Space Policy, Earth Observation, and Satellite Navigation at the European Commission (DEFIS) stated: "These first images mark an exciting step for the Copernicus component of the EU Space Programme. Sentinel-6 Michael Freilich, the first satellite in the Sentinel-6 series, already delivers essential information on sea level, ocean currents and inland waters, supporting coastal protection and climate resilience. Sentinel-6B ensures this capability continues well into the future, showing how Europe's long-term investments in space translate into tangible benefits for society."

Sentinel-6B data will feed operational ocean forecasts from the Copernicus Marine Service, improve weather and seasonal prediction, and support long-term ocean and climate monitoring.

Satellite reaches final orbit — tandem flight begins
On 16 December, Sentinel-6B reached its final orbit at 1,336 km above Earth. The satellite is now flying just 30 seconds behind its predecessor, Sentinel-6 Michael Freilich, and will remain in this position for about ten months. This tandem phase will allow exceptionally precise cross-calibration of sea-level measurements — to within a fraction of a millimetre - ensuring a seamless continuation of the 30-year climate-quality sea-level record used worldwide, which is essential for understanding sea-level rise.

The Copernicus Sentinel-6 mission is the High-Precision Altimetry reference mission, against which other international altimetry missions are calibrated. Once operational, Sentinel-6B will replace Sentinel-6 Michael Freilich as the new reference altimetry satellite, while the latter will then move its ground track to interleave with Sentinel-6B, so optimising their combined observation of the global oceans. The continuation of such observations beyond 2030 is planned with a Sentinel-6C satellite, currently under discussion among the partners.

The Copernicus Sentinel-6 mission is the result of a partnership between the European Commission, Eumetsat, the European Space Agency (ESA), the US National Aeronautics and Space Administration (Nasa), the U.S. National Oceanic and Atmospheric Administration (Noaa), with support from the Centre National d’Études Spatiales (Cnes).

Images and further mission updates are available via Eumetsat's Sentinel-6B launch hub.

(news from Eumetsat)

See also:
https://cnes.fr/en/projects/sentinel-6
https://science.nasa.gov/mission/sentinel-6b/
https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-6

Part of the European Copernicus program, this operational mission ensures the continuity and stability of measurements which are essential to the climate series initiated by the US-French Topex/Poseidon mission in 1992, then continued by the Jason satellites and more recently by Sentinel-6A Michael Freilich in 2020.

The satellite carries a payload consisting mainly of a radar altimeter, a microwave radiometer, and a satellite positioning system including three different instruments. These four systems enable it to provide us with valuable data on the oceans: by measuring the time elapsed between the emission, the reflection on the ocean, and the reception of the radar signal, it is possible to deduce the height of the water surface. To do this, the satellite also measures the water vapor content of the atmosphere, while engineers on the ground determine its position with great precision (to within a centimeter!) using the positionning system (GNSS, Doris and the laser reflector).

Doris, an essential ally for the mission

To ensure long-term measurement stability and reduce the uncertainty of sea level measurements by between 0.1 and 0.3 mm/year over 10 years, the GNSS system is combined with the Doris (Doppler Orbitography and Radiopositioning Integrated by Satellite) system, developed by Cnes. Used on numerous missions since the 1990s, this system, consisting of a global network of more than 60 ground beacons, is an unfailing ally for altimetry missions. Without precise knowledge of the satellite's position, provided by the GNSS/Doris combination, it is impossible to determine the distance traveled by the radar signal between the ocean surface and the satellite. 
"In addition to improving the stability of the orbit solution and enabling the quantification of its uncertainty, which is essential for climate activities, the Doris instrument is also used to provide the satellite with a priori knowledge of its location on board. This information, combined with a digital terrain model loaded on board, enables the Poseidon-4 altimeter to know when it can expect to receive the return signal that we want to measure. This is essential for coastal oceanography, hydrology, and continental ice measurement, where the topography varies rapidly. Without this capability, we would have virtually no data in these important geographical areas. This is one of the key areas of expertise that CNES brings to the program. " (Lionel Zawadzki, Sentinel-6B project manager at Cnes)

Anticipating the impacts of sea level rise

To carry out its mission, Sentinel-6B orbits at an altitude of 1,336 km and an inclination of 66 degrees, enabling it to observe 90% of the ice-free ocean surface. In addition to sea surface heights, it provides near real-time information on significant wave heights and surface wind speeds. The satellite will also provide more detailed data on water eleveations near coasts, sea ice, and continental ice, thanks to advances in radar altimetry techniques developed during the Sentinel-3 and CryoSat missions.

This essential data, combined with data from the entire altimetry constellation, will provide a better understanding of local dynamics and enable us to anticipate the impacts of sea level rise on populations and territories. In France alone, more than 6.4 million people live near the coast and depend directly on the maritime economy, tourism, or coastal resources. However, between 1993 and 2025 altimetry satellites revealed an average rise in sea levels of more than 10 cm... This phenomenon, caused by the melting of glaciers in Antarctica and Greenland, as well as by the thermal expansion of the oceans linked to their warming, has a direct impact on maritime activities and the coastline, where coastal erosion is becoming increasingly visible.

The role of Cnes in the Sentinel-6 program

With over 30 years of expertise in space altimetry missions thanks to the Topex/Poseidon mission, followed by the Jason series of satellites and, more recently, Sentinel-6A Michael Freilich, Cnes supports the entire program, from the development phases to data exploitation, in order to guarantee the highest level of performance and quality of the data produced: system expertise during the development phase, R&D in algorithms and science, operational production of orbit solutions and geophysical corrections, definition of the onboard digital terrain model, analysis of the altimetry system's performance during the CalVal phase and then during the operational phase, operational production of L2P/L3 products for Copernicus core services, etc.

Launch replay:
https://www.youtube.com/@NASA 

More information on Sentinel-6B and its journey to California at ESA Sea-level monitoring satellite Sentinel-6B sets sail

The cooperation has broadened, with other organizations, and also Europe joining in, in the frame of the Copernicus Sentinel program. 

Jason-3 is still up and functionning and should be shifted on a new orbit next year, to complement the coverage of Sentinel-6 Michael Freilich (also called "Jason-CS") and deliver data for some more years.

New stage, since this reference mission is now fully part of the Copernicus operational constellation of satellites, a "Sentinel", with a clone already nearly ready, built and tested. It will be launched to take over Sentinel-6 Michael Freilich, after the same intercalibration with its predecessor. Moreover, the use of the "SAR mode" for all the oceans opens new capabilities. Some are already being developped (such as fully-focused SAR), some might still arise.

See also: Monitoring of the Earthâs oceans from space enters a new era (Eumetsat),  New sea-level monitoring satellite goes live (Esa, with some calval results), Major Ocean-Observing Satellite Starts Providing Science Data (Nasa)

The CNES contribution includes the provision of improved and calibrated sea surface height and wave products that will be used by CMEMS to generates forecasts and maps of ocean parameters such as temperature, salinity or currents, the performance chain of measurement (CAL/VAL) and accurate orbit restitution.
Sentinel-6 extends the reference altimeter mission of Topex/Poseidon (1992-2006) and Jason series (Jason-1 2001-2013; Jason-2 2008-2019; Jason-3 2016) and thus continues the long-term recording of sea surface height measurements.

These long time series are fundamental for understanding the ocean's role as a mitigator of climate change, for understanding all components of climate, including the "slow" variations in climate: ocean circulation, melting of the polar ice caps and their consequences on sea level rise.

Further information

• Missions : Sentinel-6
• On ESA website : Sentinel-6, Discussing sea-level rise and Sentinel-6

The HaiYang-2B (HY2B) mission has been launched on October 25th, 2018. It is a marine remote sensing satellite developed by the China's National Satellite Ocean Application Service (NSOAS). The objective of the mission is to monitor the dynamic ocean environment. HY2B carries a classic LRM altimeter on the same 14-day repeat orbit as HaiYang-2A currently used in the DUACS Delayed Time system.

As detailed in (Labroue et al, OSTST 2019) and in the routine statistics available on the dedicated DUACS page there is a good agreement of HY2B measurements with other altimeters and particularly a lower noise level for HY2B compared to Jason-3.

Daily statistics of Sea Level Anomaly (SLA) standard deviation in meters for Jason-3 in red and HY2B in blue showing a good quality of HY2B measurements

Noise level of SWH (left) and SLA (right) measurements for HY2B and Jason-3

HY2B in DUACS since the 7^th of July

Since the 7th of July 2020, the DUACS Near Real Time system has been using the HY2B altimeter measurement, bringing to 6 the number of altimeter missions processed. Opposite figure shows the contribution of each satellite to the gridded products. HY2B has a 14% contribution over the July-August period. In particular, HY2B strongly helped to limit the impact of the loss of Cryosat-2 data, temporarily disactivated in the system, and the gaps in Altika measurements due to stronger than usual mispointing events. The contribution of HY2B could still be increased by 2-4% (higher than Cryosat-2) by improving the timeliness of the products, ie using OGDR based products, with a few hours of delay.

Mean contribution (DFS) in % of each satellite to the gridded products

SWH measurements

The noise level of HY2B SWH measurements is lower than Jason-3 (see Labroue et al, OSTST 2019) showing its good quality. An illustration of the interest of HY2B SWH is detailed during the Laura Hurricane (see AVISO+ web Page)  where HY2B measured wind and wave parameters on August 25 and 26 when flying over the Hurricane.

The future with HaiYang-2C

The next altimeter HaiYang-2C of the same family as HaiYang-2A and 2B has been launched on September 21st. It will be integrated into DUACS as soon as the data are available and assessed, to reinforce the resilience of the system and improve the multimission products quality.

These new products are processed by the Sentinel-3 L2P/L3 Marine Altimetry Service (CNES/CLS), in the frame of a EUMETSAT contract, part of the COPERNICUS Programme funded by the European Union. 

The products are available in Near-Real Time and the service is pre-operational till mid-june 2019. 

Please refer to the

product sheet and disclaimer for more information. The details about the processing is described in the

Product handbook.

Dissemination:

Sentinel-3 L2P are disseminated by AVISO+ (via ftp or AVISO+ CNES Data Center) and will also be disseminated by EUMETSAT via EUMETCast once the service will be fully operational, i.e. mid-June 2019.

AVISO+ Access:

• For new users, please see information and registration on the product page
• For AVISO+ registered users, please, choose the product "Wave Along-track Level-2+ (L2P) Sentinel-3â in your private page

Dissemination:

AVISO+ access:

• Ocean and Land Colour Instrument (OLCI),
• Sea and Land Surface Temperature Radiometer (SLSTR), 
• SAR Radar Altimeter (SRAL), 
• MicroWave Radiometer (MWR), 

• DORIS receiver (Doppler Orbitography and Radiopositioning Integrated by Satellite)
• GNSS receiver (Global Navigation Satellite System)
• LRR (Laser Retro Reflector)

• the input data are the âspring 2017 reprocessedâ version of input NTC L2 products fully detailed in the EUMETSAT S3A STM reprocessing technical note
• the standards are the same as in 01_00 version
• new cycles are available (cycles 5 to 11)

The Products

• The update of geophysical standards to calculate sea level anomalies, such as
  • FES2014 ocean tide
  • CNES/CLS 2015 mean sea surface referenced to a 20 year reference period
  • Filtered ionospheric correction
  • Dynamical atmospheric correction for L2P NRT products (instead of only inverted barometer height correction in the case of L2 NRT products).
• A validity flag to remove spurious measurements
• The distribution of L2P SLA near real time products splitted in passes (instead of 10 minute granules for L2 near real time products).

The dissemination

The L2P STC/NRT products are also available through EUMETSAT dissemination via EumetCast.