Sentinel-6: the “Dog Kennel” satellite leaves for the ocean mission

A satellite that will be critical to understanding climate change has exploded skyward from California.

Sentinel-6 “Michael Freilich” is set to become the primary means of measuring the shape of the world’s oceans.

Its data will not only track sea level rise, but will reveal how the great mass of water is moving around the globe.

Resembling a bit like a kennel, the sophisticated 1.3-ton satellite was carried aloft from the Vandenberg base on a SpaceX Falcon-9 rocket.

The Sentinel is a joint effort between Europe and the United States, and will continue measurements that have been made by a series of spacecraft, called the Jason-Topex / Poseidon series, dating back to 1992.

These previous missions have unequivocally demonstrated that the global sea level is rising, at a rate of more than 3mm per year over a period of 28 years. And their most recent data even suggests an acceleration is underway, with levels recorded increasing by more than 4mm per year.

About a third of the global sea level rise measured on Earth comes from the expansion of water warming, a key factor of which is climate change. The rest is largely due to the melting of the ice.

Sentinel-6, like all previous satellites, will use a radar altimeter to assess the height of the oceans.

This instrument sends a microwave pulse to the surface and then counts the time it takes to receive the return signal, converting it into an elevation.

Sentinel-6, however, will fly with a much improved capacity, which will allow it to see more clearly what the seas are doing right against the coasts; and also how the characteristics of inland waters – rivers and lakes – behave.

Elevation is a key parameter for oceanographers. Just as the surface air pressure reveals what the atmosphere above is doing, so the height of the ocean will reveal the details of the behavior of the water below.

The data provides clues to temperature and salinity. When combined with gravity information, it will also indicate the current direction and speed.

Oceans store large amounts of heat from the sun; and how they move that energy around the world and interact with the atmosphere is what drives our climate system.

But having the longest possible record of the change is essential.

“The longer the time series, the better we are able to separate natural climatic signals from forced ones, from the human signal,” explained Craig Donlon, mission scientist of the European Space Agency.

“It means we can run the climate models backwards and then, through a validation process, be confident that when we run them forward we have some predictive capability.”

The oceans are not increasing at the same rate everywhere. There are parts of the world where the elevation exceeds 1 cm per year.

This is due to a multitude of factors, including changes in ocean circulation, changes in heat content, and uneven dispersion of meltwater from ice sheets.

It is a somewhat recognized fact that discharge from powerful glaciers, such as the Thwaites Glacier in Antarctica, has the greatest effect on ocean height at great distances.

“Sea level rise is not uniform; it’s really important to recognize that,” Christine Gommenginger, of the UK’s National Oceanography Center (NOC) in Southampton, told BBC News.

“It’s the regional sea-level budgets that we’re now targeting. Global sea level rise – well, we know. But it’s the local picture we want, and the altimetry can give it.”

Oceanographers and climatologists, of course. But the data is also of extreme importance to meteorologists.

In the return signal there is information about the state of the ocean – about how rough it is, which also speaks of the strength of the winds.

The ocean and its connection to the atmosphere are perhaps best illustrated by hurricanes. These storms draw their energy from tropical warm water that an altimeter can sense from the way the sea surface swells.

And it’s satellites like Sentinel-6 that sound the alarm of an El Niño event, which sees warm waters in the western Pacific shift east. This triggers a global perturbation in weather systems, redistributing rainfall and increasing temperatures.

“Other users include ship routes: they don’t want their ships to go through storms; they want to avoid big waves,” said Remko Scharroo, of the intergovernmental weather agency Eumetsat. “With the Sentinel-6 altimeter, we will also see eddies in the ocean, and if you are a ships router this information will tell you how to go with the current, not against it.”

It goes without saying that coastal and flood defense planning depends on elevation data. No new nuclear power plant can be built without understanding where high tides and storm surges could reach decades in the future.

The nickname “Sentinel” is the name given to all the satellites of the Copernicus Earth observation program of the European Union, of which this mission is a part.

Its number shows that it is the sixth in the series of different types of sensors planned for the network.

The name Michael Freilich commemorates the former director of the Earth Sciences division of the US space agency NASA, who died earlier this year. He was an oceanographer by background and was instrumental in putting together the international partnership behind the mission.

“Mike Freilich exemplified the commitment to excellence, the generosity of spirit and the unparalleled ability to inspire trust that has driven so many people around the world to want to work with NASA, to promote great goals on behalf of the planet. and its people, “commented Thomas Zurbuchen, who heads the scientific direction of NASA.

British engineers built the propulsion module on Sentinel-6. It has eight 5-newton thrusters that will help keep the 1.3-ton satellite in the very precise orbit required to make its measurements.

The module is a kind of plug and play unit that can be easily incorporated into other spacecraft.

“Because we have recurring equipment, it means we can make bulk purchases with cost savings,” said Natasha Pushkin of Airbus UK. “And because we have reusable building blocks, it means projects and processes can be established in advance, which saves time.”

Additional modules will be added to Sentinel-6 successor Michael Freilich and next generation polar-orbiting weather satellites in Europe.

But beyond the industrial contribution, British scientists and agencies will be big users of the data – to the NOC to understand the broader behavior of the oceans and to the UK Met Office to feed its data into the numerical models they produce the next day. , medium and long-term weather forecasts.

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