Mapping Sea-Level Rise with Sentinel-6

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On November 21st, Sentinel-6 was launched by the European Space Agency (ESA) using a SpaceX Falcon 9 rocket. The satellite was developed in partnership with NASA and other agencies and was named after former NASA Earth Science Division Director Michael Freilich.[1] 

The recent launch of Sentinel-6 Michael Freilich/Jason CS is the latest mission that will collect sea level measurements at more frequent intervals to monitor the effects of climate change on our oceans. With one of the biggest threats of climate change being the rise of ocean levels, this represents an important tool for scientists planning and mapping the Earth’s response to climate change. 

Current sea levels are rising at a rate of 3.6 centimeters per decade. As this rise continues to accelerate, measuring the height of the ocean is a key component of understanding the effects of climate change.

The Sentinel-6 satellite is an altimeter-focused instrument, representing a continuity of satellite systems used to monitor oceans since the early 1990s. Sentinel-6 will serve as the reference mission for sea-surface height measurement. Intended to be a two-satellite mission, the second Sentinel-6 satellite is scheduled to launch in 2025 to complement the current system.

Artistic rendering of the Sentinel-6 Michael Freilich satellite.  Image: Credits: NASA/JPL-Caltech
Artistic rendering of the Sentinel-6 Michael Freilich satellite. Image: Credits: NASA/JPL-Caltech

Additional instruments onboard the satellites also be used to provide weather data, including atmospheric data to improve climate models and hurricane tracking.[2]

In 1992, the mission of measuring sea-level rise began with the TOPEX/Poseidon satellite and continued with Jason-1 (2001), OSTM/Jason-2 (2008), and, in 2016, Jason-3.  The launch of the Sentinel-6 satellites will ensure a continuity in sea level observations out to 2030. Sentinel-6 has both a low-resolution and a high-resolution observing mode to ensure compatibility with prior missions.

Sentinel-6 carries the European Poseidon-4 altimeter that uses, for the first time, a synthetic aperture radar capability to the altimeter reference mission time series. This will allow measurements of sea levels to be within a few centimeters.

Data also allow the collection of high resolution vertical profiles of temperature data, where a GNSS Radio-Occultation sounding technique is used to monitor change in the temperature profile. This makes it able to take measurements in the troposphere and stratosphere, including the modeling of these profiles for forecasting purposes. [3]

Measuring Sea Level Rise

Sentinel-6 continues a record of nearly thirty years of data that have already measured a progressive rise of sea levels. Since the French-US Topex/Poseidon mission, precision now allows us to make realistic averages on how rapidly sea levels are changing.

Sea level rise is a threat to low-lying coastal populations.  Photo shows results of wave-driven flooding and overwash on Roi-Namur Atoll, Republic of the Marshall Islands. Photo: Peter Swarzenski, USGS. Public domain.
Sea level rise is a threat to low-lying coastal populations. Photo shows results of wave-driven flooding and overwash on Roi-Namur Atoll, Republic of the Marshall Islands. Photo: Peter Swarzenski, USGS. Public domain.

Back in the 1990s, sea level change showed about a 3.1 mm/year increase. In the 2000s, it increased 3.6 mm/year. Between 2013-2018, the rate increased to increased to 4.8 mm/year.

Scientists have observed the fact that this increasing rate is not uniform across the globe, with some regions appearing to have more rapid increase.

Instruments from Sentinel-6 will, therefore, be important because it can show precise levels of sea level change across different regions, allowing scientists to analyze where the greatest threats to sea level change are most likely to be. With the majority of the planet’s population living near coastal regions, forecasting where regions are likely to face near- and long-term threats will be crucial as adaptation to climate change will increasingly be paramount in global policies.[4]

Storm and sea level rise scenario model for Dauphin Island, Alabama. This model shows what Dauphin Island may look like 10 years from now if storms become stronger and more frequent (Passeri and others, 2018). Map: RC Mickey, USGS. Public domain.
Storm and sea level rise scenario model for Dauphin Island, Alabama. This model shows what Dauphin Island may look like 10 years from now if storms become stronger and more frequent (Passeri et al., 2018). Map: RC Mickey, USGS. Public domain.

 Data should become available within three to three and a half months of launch, with near real-time low resolution data made available. A dedicated FTP server will be provided to enable scientists around the world to utilize the data as they become available.[5]

The Sentinel-6 is the next generation of sea level monitoring altimeter monitoring tools that have increasingly improved accuracy since the 1990s. Scientists now can monitor sea level change within centimeters of their true accuracy across the globe. Data we have clearly show an accelerating level of sea level change and it is expected that Sentinel-6 will not only confirm this but also better forecast change for different regions. 

References

[1]    For more on Sentinel-6 and sea level  rise, see: http://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-6.

[2]    For more on background data on Sentinel-6 and its development to monitor oceans, see:  https://www.nasa.gov/feature/jpl/sentinel-6-michael-freilich-satellite-prepared-for-launch.

[3]    For more on the instrumentation and goals of Sentinel-6, see: https://www.eumetsat.int/sentinel-6.

[4]    For more on monitoring sea level change, and regional threats that data demonstrate, see:  Pultarova, T., 2020. Satellite – Monitoring. The seas are rising – but how fast? Engineering & Technology 15, 56–58. https://doi.org/10.1049/et.2020.0108

[5]    For more on data release and where to get information on data, see:  https://www.eumetsat.int/sentinel-6-data-release-and-access.


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