The sea level observer takes flight

A joint US-European satellite, built to monitor sea level around the world, lifted off on a SpaceX Falcon 9 rocket from Vandenberg Air Force Base just after 9 a.m. PT on November 21, 2020. About the size from a small van, Sentinel- 6 Michael Freilich will expand a nearly 30-year continuous data set on sea surface height.

The satellite’s primary instrument is a radar altimeter, which monitors the height and shape of ocean ridges and valleys – known to scientists as ocean surface topography. Radar altimeters continuously send pulses of radio waves (microwaves) that bounce off the ocean surface and reflect back to the satellite. The instrument calculates the time it takes for the signal to return, while tracking the precise location of the satellite in space. From there, scientists can calculate the height of the sea surface directly below the satellite.

Sentinel-6 Michael Freilich will continue a sea level record that began in 1992 with the TOPEX / Poseidon satellite and continued with Jason-1 (2001), OSTM / Jason-2 (2008) and Jason-3 ( 2016). Together, these satellites have provided accurate long-term measurements of sea level height while tracking the rate at which our oceans are rising in response to global warming. Sentinel-6 Michael Freilich will finally hand over the baton to his twin, Sentinel-6B, which is scheduled for launch in 2025.

“Together, these satellites will allow us to continue measuring global sea level for another full decade,” said Josh Willis, NASA’s project scientist for the mission and oceans specialist at NASA’s Jet Propulsion Laboratory. “This is the first time we have been able to launch one when its predecessor is still young. Jason-3 is still in its design lifespan, and that’s a big deal for us because to keep the record accurate when it’s transferred from satellite to satellite, we really need them to overlap to be able to cross-calibrate.

The time-lapse video above shows the Falcon 9’s exhaust plume within 25 minutes of the rocket launching from California. Images were acquired with the Advanced Baseline Imager (band 2 / red) on GOES-17. The satellite is operated by the National Oceanic and Atmospheric Administration (NOAA), and NASA is helping to develop and launch the GOES series.

The spacecraft is named in honor of Michael Freilich, former director of NASA’s Earth Sciences Division and a leader in advancing ocean observations from space. Freilich retired in 2019 and passed away on August 5, 2020. Close family and friends attended the launch of the satellite that now bears his name.

“Michael was a tireless force in the earth sciences. Climate change and sea level rise know no national borders, and he has championed international collaboration to meet the challenge, ”said Josef Aschbacher, director of observing programs at the Earth for the European Space Agency (ESA). “It’s only fitting that a satellite in his name will continue to serve as a ‘benchmark’ for sea level measurements for the next half decade.”

“The Earth is changing and this satellite will help us deepen our understanding of how,” said Karen St. Germain, director of NASA’s Earth Sciences Division. “Earth’s changing processes affect sea level globally, but the impact on local communities varies widely. International collaboration is essential both to understand these changes and to inform coastal communities around the world.

After entering orbit, the spacecraft separated from the second stage of the rocket and unfolded its two sets of solar panels. The ground controllers successfully acquired the signal from the satellite, and the first telemetry reports showed the spacecraft to be in good health. Sentinel-6 Michael Freilich will now undergo a series of exhaustive checks and calibrations before starting to collect scientific data in a few months.

The initial orbit of Sentinel-6 Michael Freilich is approximately 20 kilometers (12 miles) lower than its ultimate operational orbit of 1336 kilometers (830 miles). In about a month, the satellite will receive commands to raise its orbit, trailing Jason-3 for about 30 seconds. Scientists and engineers on the mission will then spend about a year calibrating the data collected by the two satellites. Sentinel-6 Michael Freilich will then take over as the primary sea level satellite and Jason-3 will provide a support role until the end of his mission. Scientific instruments from the two satellites will also take atmospheric measurements that can be used to supplement climate models and help meteorologists make better weather forecasts.

Sentinel-6 Michael Freilich and Sentinel-6B make up the Sentinel-6 / Jason-CS (Continuity of Service) mission developed in partnership with ESA, NASA and NOAA. NASA’s JPL supplies three scientific instruments to each Sentinel-6 satellite: the Advanced Microwave Climate Radiometer, the Global Navigation Satellite System – Radio Occultation, and the Laser Retroreflector Network. NASA also provides launch services, ground systems and data medium, and support for the US component of the International Ocean Surface Survey Science Team.

To learn more about the height of the sea surface and the long international collaboration to study it, read Taking a Measurement of Sea Level Rise: Ocean Altimetry.

To learn more about Sentinel-6 Michael Freilich, visit the mission home pages at the European Space Agency, NASA, the European Union’s Copernicus program, and EUMETSAT.

Looking for sea level rise data? The Sea Level Change Data Pathfinder on NASA’s Earthdata site highlights the tools used by researchers to study ocean altimetry, including integrated multi-mission ocean altimeter data for climate research.

Video from NASA’s Earth Observatory by Joshua Stevens, using GOES 17 data from NOAA and the National Centers for Environmental Information (NCEI). Photographs courtesy of SpaceX. Story assembled from NASA and ESA press releases by Mike Carlowicz.