NASA and ESA’s next Earth Observing science mission aims to better understand sea level rise and how it changes over time, as coastal communities around the world see more and more the affects of the Earth’s global climate warming. The joint U.S.-European Sentinel-6 ‘Michael Freilich’ satellite intends to collect the most accurate data thus far on how climate change is affecting the oceans, with millimeter-scale precision, and is now in the final stretch for launch later this month from Vandenberg AFB, CA.
The spacecraft, named after Dr. Michael Freilich, former director of NASA’s Earth Science Division who was instrumental in advancing ocean observations from space, recently competed final checkouts and has since been encapsulated within the rocket’s bullet-like protective aerodynamic payload fairings. The next step now is to transport the satellite to meet and join its Falcon 9 rocket, slated for launch no sooner than Nov 21 at 9:17 a.m. PST from Space Launch Complex 4E.
The spacecraft is part of Sentinel-6/Jason-CS, a 10-year mission by U.S and European agencies to continue studying rising sea levels across more than 90% of the world’s oceans, and actually consists of two identical satellites launching five years apart, Sentinel 6A (launching in Nov) and Sentinel 6B in 2025. They follow four other joint U.S.-European missions — TOPEX/Poseidon and Jason-1, Ocean Surface Topography/Jason-2, and Jason-3 — that over the past thirty years have documented Earth’s oceans rising by an average of 0.13 inches (3.3 mm) per year, more than twice the rate at the start of the 20th century (source NASA).
“As more and more people move to coastal regions, and coastal megacities continue to develop, the impact of sea level change will be more profound on those societies,” said Craig Donlon, mission project scientist at the European Space Agency.
The mission was set to launch in early Nov, but an on-pad abort during a non-NASA mission in Oct forced NASA and SpaceX to standby on all Falcon 9 launches while an investigation got underway. After completing engine testing and inspections, teams determined that two engines on the Sentinel-6 rocket’s first stage would need to be replaced to ensure optimal performance during launch. Work is now progressing to implement the engine change and all engine hardware replacements will finish next week, says NASA.
“Some of the long-term datasets climate scientists rely on, like ocean temperature or the height of tides, have gaps or major changes in how data was collected (like before and after satellite records began) that make understanding the long-term climate signal challenging,” says NASA. “Researchers must account for these variations to ensure that their results are truly representative of the phenomena they’re looking at.”
Continuity is key to the dataset’s success, which is why each of the previous satellites all launched into the same orbits, and before the older one was decommissioned. Sentinel 6A for example, will orbit at an altitude of 1,300km (800 miles) and be inclined over the equator, following 30 seconds behind the Jason-3 satellite, which launched in 2016 atop another SpaceX Falcon 9 from Vandenberg. Being inclined to the equator will allow Sentinel-6 to cover 2/3 of the entire planet every 10 days
Scientists will then spend a year cross-calibrating the data collected by Jason-3 and Sentinel 6A, ensuring the continuity of measurements from one mission to the next, and they’ll do the same again once Sentinel 6B launches in 2025.
“This new earth observing satellite will give us the ability to track and understand sea level rise like never before,” says Josh Willis, the missions’s Project Scientist from NASA JPL. “It will extend the record of sea level rise for another decade, past the 30 years we already have, and allow us to see how sea levels are not only rising, but how it’s accelerating.”
“Sea levels are rising at a faster and faster rate every decade,” he adds. “We need these measurements to predict how quickly flooding will increase across the planet.”
But Sentinel-6/Jason-CS won’t just study sea level change; it will also record changes in ocean circulation, climate variability such as El Niño and La Niña, and weather patterns such as hurricanes and storms, providing atmospheric data that will improve weather forecasts and bolster climate models. The mission will also collect measurements at higher resolution than any of the previous satellites, and measure smaller sea level variations near coastlines; something none of the previous missions could do.
Understanding weather phenomena such as El Niño and La Niña are critically important to people around the world, as each have very significant impacts across every continent. An El Niño, for example, can shift ocean currents and global weather patterns, bringing torrential rain to the Southwestern U.S. and triggering droughts in Asia and Australia. La Niña, meanwhile, has the opposite effect.
“In 2010, there was a massive La Niña and it essentially flooded huge parts of Australia and Southeast Asia. It rained so much on land, it dropped global sea levels by one centimeter [0.4 inches],” said Willis. “We had no idea it could have such a massive impact on global sea level.”
“The Sentinel-6 Michael Freilich satellite will advance our understanding of the Earth as a system, and inform decision-makers, from federal to local levels, who must manage the risks associated with rising sea levels,” said Karen St. Germain, director of NASA’s Earth Science Division in Washington.
It’s being jointly developed by the European Space Agency (ESA), the European Organisation for the Exploitation of Meteorological Satellite (EUMETSAT), NASA and the National Oceanic and Atmospheric Administration (NOAA), with funding support from the European Commission and support from France’s National Centre for Space Studies (CNES).
A Ku/C Radar Altimeter called POSEIDON-4 will be the primary measurement system, capable of acquiring “phase coherent measurements of a surface allowing synthetic-aperture processing to improve along-track sampling and reducing range and Significant Wave Height (SWH) noise as a function of SWH,” according to ESA.
The main characteristics of the POSEIDON-4 (SENTINEL-6 Ku/C radar altimeter) are:
- Radar measurement modes: Interleaved mode (simultaneous LRM and SAR, plus reduced-data-rate-SAR RMC
- Ku-band central frequency of 13.575 GHz, total bandwidth of 320 MHz
- C-band secondary frequency, used for ionosphere corrections, central frequency of 5.41 GHz, total bandwidth of 320 MHz
- Tracking modes: closed and open-loop
- Pulse repetition frequency: approximately 9 kHz (variable from 9.076 to 9.280 kHz)
- With the current POSEIDON-4 design theoretical performances have been assessed which demonstrates that SENTINEL-6 will improve on its required performances for both LRM and SAR processing.
NASA meanwhile is providing three science instruments for both satellites: an Advanced Microwave Radiometer, a Global Navigation Satellite System – Radio Occultation instrument which will use radio occultation to measure the physical properties of Earth’s atmosphere (another big key piece to the climate change puzzle), and a Laser Retroreflector Array.
NASA’s Launch Services Program is responsible for launch management. The agency is also providing the ground systems supporting the science instruments operations and giving support for the international Ocean Surface Topography Science Team.