OBSERVER: How Sentinel-6 Michael Freilich improves the Copernicus Marine Service Ocean Data Catalogue

OBSERVER: How Sentinel-6 Michael Freilich improves the Copernicus Marine Service Ocean Data Catalogue

OBSERVER: How Sentinel-6 Michael Freilich improves the Copernicus Marine Service Ocean Data Catalogue
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Thu, 23/06/2022 – 09:17

The Sentinel-6 Michael Freilich. Credit: ESA

Following Jason-3, the Copernicus Sentinel-6 Michael Freilich is now the new reference altimetry mission satellite to provide the most precise sea level data in the world. This unique feature has allowed for Sentinel-6 Michael Freilich to support publications and recommendations from the International Panel on Climate Change specially in terms of sea level rise monitoring and projection. This new mission is an important step in continuing in the future the long-term uninterrupted recording of mean sea level from satellite radar altimeters from the past 30 years. As Jason series used to do, Sentinel-6 Michael Freilichwill now pursue the important mission to deliver the reference data needed to cross-calibrate sea level and wave measurements from all other satellite altimetry missions across the globe. Moreover, this mission will improve the quality of approximately 60% of the Copernicus Marine Service ocean data catalogue.

How do Ocean Monitoring Indicators monitor the health of the ocean?

As global temperatures climb, so does sea level as a result of land-ice melt and thermal expansion (so-called thermosteric sea-level rise). The acceleration of this rise is cause for grave concern given the impacts on coastal communities, ecosystems, and economies. Close monitoring of sea level is essential for decision-makers to develop data-informed mitigation and adaptation strategies. Launched in November 2020, Sentinel-6 Michael Freilichis the latest to join the family of Copernicus Sentinel satellites collecting essential data to better understand the state of our planet. Much like its predecessors with the Jason series, Sentinel-6 Michael Freilich will improve marine meteorology, assessing seasonal trends in sea level anomaly and waves, and monitoring the speed of sea surface currents. Perhaps most importantly, it will monitor the rise in sea levels which have been referred to as the “thermometer” for climate change. This type of data is used in seminal reports like those of the IPCC and WMO, that track and assess the changing state of the global ocean and climate.

Source: ESA

Expanding the Copernicus Marine Catalogue

In the words of Pierre-Yves Le Traon, Scientific Director at Mercator Ocean International, the European Commission’s Entrusted Entity to implement Copernicus Marine, The addition of Sentinel-6 data marks a major milestone in tracking sea level rise from global to coastal scales and improving over half of our catalogue, both with high accuracy sea level observations and by increasing the quality of our ocean forecasts through data assimilation.”

With more than 450,000 users globally, Copernicus Marine provides ocean information products across the Blue (physical), White (sea ice) and Green (biogeochemical) ocean. New Sentinel-6 Michael Freilichdata is expected to improve more than half of its observation and modelling product portfolio. Since April 2022, Sentinel-6 Michael Freilichobservations on sea level and waves have been added to the catalogue. These additions to the satellite observation components comprise about half of the expected improvement, and the second half will benefit the model products in the coming months.  All this will improve an impressive 60% of the Copernicus Marine observation and modelling products.

For example, the Copernicus Marine real-time global ocean sea surface height data product directly  benefits from the new Sentinel-6 Michael Freilich. It processes data from all altimeter missions that are now flying: Sentinel-6 Michael Freilich, Jason-3, Sentinel-3A & 3B, HY-2A, Saral/AltiKa, Cryosat-2. The global and regional ocean real-time models now also benefit from Sentinel-6 through data assimilation. Data assimilation methods apply a data-driven constraint on the model results. Such numerical models assimilate as much observed data as possible from in situ or satellite sources. Sentinel-6 Michael Freilichtogether with other altimeter missions (in particular S3A&B and Jason-3) provide essential and unique information to constrain ocean models.   

Sentinel-6 Michael Freilichdata will also be used by the Copernicus Climate Change Service (C3S) to deliver climate reprocessed sea level data (an Essential Climate Variable) that are unique datasets to monitor the long-term evolution of sea level (see the Copernicus Marine and Copernicus Climate change Indicators Global Ocean Mean Sea Level time series and trend from Observations Reprocessing).

Processing the data into Ocean Products

After the addition of Sentinel-6 Michael Freilichmeasurements to the sea level and wave observations already in place using Sentinel-3 and all available altimetry contributing missions, various models will undergo the process of data assimilation in which Earth Observation data, Sentinel-6 Michael Freilichin this case, is injected into numerical forecast models to increase their accuracy. Many of our global and regional physical and wave models will undergo these updates in the coming months.

To benefit from Sentinel-6 Michael Freilich, the Copernicus Marine Service relies on the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), which operates the Sentinel-6 Michael Freilichdata delivery. EUMETSAT, is responsible for data processing and dissemination of Level-1 (L1) to Level-2 (L2) Sentinel-6 Michael Freilichsea level products as well as global Level-3 (L3) data processing.

Building on it, The Copernicus Marine Service’s Sea Level Thematic Assembly Centre (SL TAC), led by CLS, transforms and disseminates these data into regional L3 and L4 sea level products combining data from many satellite altimeters flying combined with Sentinel 3 satellites and using Sentinel-6 Michael Freilich as reference, so that our service can track sea level, or surface currents.

Marie Isabelle Pujol of CLS and service manager or the Copernicus SL TAC noted that,

“The integration of Sentinel-6 Michael Freilichinto the SL TAC system is an important step. Sentinel-6 Michael Freilichis now the new reference mission in our system. This means that the sea surface height (SSH) measured by Sentinel-6 Michael Freilichis used as a reference to calibrate the SSH measured by the other altimeters, at the global but also regional scale. Sentinel-6 Michael Freilich will therefore guarantee the continuity of the measurement of the mean sea level in the next years. Moreover, the SAR mode available on Sentinel-6 Michael Freilichallows us to reduce the measurement noise and thus to improve the quality of the products and to increase the resolution of these products for the observation of the signal at smaller scales“.

To learn more about the products currently improved by the Sentinel-6 Michael Freilichingestion click here.

Sea Surface Height above sea level. Credit: Copernicus Marine MyOceanPro viewer.

Why is Sentinel-6 Michael Freilich a Game-changer?

Sentinel-6 Michael Freilich uses a radar altimeter to observe changes in sea-surface topography with centimetre precision providing, for example, insights into global sea levels. Sentinel-6 Michael Freilich is hence key to monitoring sea level rise. Sea level rise is one of the main indicators of climate change. Calculations in the fifth Copernicus Marine Ocean State Report reveal that sea level rose by about 3.1 mm on average a year since 1993 and that sea level rise is accelerating with this rate increasing by 0.12+-0.073mm/year each year.

The mechanisms that enable Sentinel-6 Michael Freilich to provide the most precise data on sea level ever makes use of the latest altimetry technology and is developed in Europe. It relies on a dual band (C/Ku) and dual mode (SAR/LRM) acquisitions that ensure a better along-track sampling and reduced measurement noise. Sentinel-6’s Michael Freilich Poseidon-4 altimeter brings new high-resolution Ku-band synthetic aperture radar measurements into the altimetry reference time series. It delivers simultaneous low-resolution  (LRM) (as previous Jason missions)  and new high-resolution (SAR) measurements.

 At the same time, it is designed to be fully compatible with the historical reference altimetry time series from its predecessors. Sentinel-6 Michael Freilich is a mission fully optimised for climate monitoring thanks to a high-altitude orbit (for very precise orbit determination), to a non-sun synchronous orbit (to reduce tidal aliasing problems) and high-performance instruments (radar altimeter, radiometer, precise orbit determination). It has the same orbit as the previous TOPEX/Poseidon and Jason-1/2/3 missions, which allows for continuous and long-term sea level monitoring on the same ground tracks.  Thanks to a careful intercalibration with Jason-3 during the tandem flight phase, a very high consistency between the Jason series has been achieved.    

This next generation of Sentinel-6 Michael Freilich satellites, replacing the Jason series, which is now funded by the European Commission and enables the Copernicus Programme to sustain the heritage and long-term record on sea level data. Sentinel-6 builds on the heritage of the Jason series and is designed to complement ocean information from Sentinel-3. It is part of the European Commission’s Copernicus Programme, and involves a multi-agency partnership including: ESA, EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites), NASA-JPL (NASA Jet Propulsion Laboratory), NOAA (US National Ocean and Atmospheric Administration), and CNES (the French National Centre for Space Studies) (see more).  Sentinel-6 takes over as a reference altimetry mission from Jason-3 which has been relocated into an interleaved orbit with Sentinel-6. This will allow scientists to maximise the temporal and spatial sampling provided by the two altimetry missions.

Thu, 23/06/2022 – 12:00

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