New sea-level monitoring satellite: More accurate ocean data thanks to precise position determination by Beyond Gravity

Over the last 10 years the global mean sea level has been increasing at average by four millimeters per year. Currently, hundreds of millions of people live in low-lying coastal areas that are directly threatened by flooding. A new sea-level monitoring satellite is scheduled for launch from California (USA) on November 17. “Rising sea levels are among the most pressing environmental challenges of our time. For all Sentinel-6 satellites we provide products that truly make a difference to the mission. Every Sentinel-6 satellite is equipped with our world-leading navigation receiver, which determines the satellite’s orbital position with below one centimeter accuracy. This level of accuracy is essential for ultra-precise millimeter-level sea measurements, enabling scientists to work with more accurate ocean data,” says Oliver Grassmann, Executive Vice President Satellites at Beyond Gravity. Headquartered in Zurich, Switzerland, Beyond Gravity is a leading provider for both established customers and New Space customers. The US-European “Sentinel-6B” satellite was built by prime contractor Airbus Defence and Space in Germany. It will launch aboard a SpaceX Falcon 9 rocket.

Precise positioning for more accurate environmental data

The satellite’s precise in-orbit-position will be determined using technology from Beyond Gravity. The company’s Precise Orbit Determination Receiver (PODRIX) achieves a very high in-orbit accuracy of the satellite’s position below one centimeter utilizing on-ground post-processing. “The high accuracy is achieved through simultaneously processing of multi-frequency signals from the US GPS and European Galileo navigation satellites. This level of accuracy is even more impressive considering that the satellite will circle the Earth at a speed of around 25,000 km/h at an altitude of around 1,300 km”, says Kurt Kober, Vice President Electronic Solutions at Beyond Gravity. He adds: “The more accurate the satellite’s position is pinpointed, the more accurate the sea data provided by the satellite.” 

Enhanced overall mission performance thanks to novel PODRIX receiver

The satellite’s predecessor “Sentinel-6 Michael Freilich”, launched in November 2020, was the first satellite to use the new Precise Orbit Determination Receivers (PODRIX) from Beyond Gravity. The European Space Agency (ESA) has publicly stated that the addition of Galileo measurements has improved the quality of orbit determination significantly, thereby enhancing the overall performance of the Sentinel-6 mission*. Currently, Beyond Gravity’s navigation receivers determine the positions of around 30 satellites in space. The latest generation receivers can also compute the new High Accuracy Service provided by Galileo satellites since 2023, even further enhancing precise position determination. 

Thermal protection against extreme cold and heat

Thermal insulation from Beyond Gravity protects the environmental satellite from the extreme cold and heat it faces in space. The thermal protection is made out of several layers of ultra-thin special polyimide foils. This will keep the instrument of the satellite at the required operating temperature despite the extremely harsh thermal environment in space from -+/-200 degrees Celsius. 

Antenna sends down ocean data to Earth

The ocean-monitoring satellite uses a high-power downlink helix antenna from Beyond Gravity to send all the collected ocean data down to Earth. Unlike traditional reflector antennas, the Beyond Gravity helix antenna is compact and lightweight but as performant as a larger antenna. Beyond Gravity developed the X-band helix antenna initially for ESA earth observation programs. The company also provided the Sentinel-6 S-band telemetry, tracking and command (TTC) antennas. The antenna TTC system enables communication with the satellite and control of it. 

Computer controls the satellite

For Sentinel-6B Beyond Gravity provided the satellite’s onboard computer. The computer is the brain of the satellite and controls e.g. the satellite’s on-board power distribution, temperatures and critical actions such as the release of locking mechanisms and thruster operations.

Remote interface unit

Beyond Gravity supplied the remote interface unit for Sentinel-6B. This unit connects the onboard computer to the satellite’s platform equipment. It plays a key role in calibrating the payload instruments, analyzing real-time telemetry, managing housekeeping functions, and facilitating command exchange between the main on-board computer and subsystems. The remote interface unit also controls the interface to the propulsion system, which executes changes in the spacecraft’s direction and speed. Additionally, it manages Sentinel-6B’s attitude and orbit control. Precise orientation in orbit is essential for the optimal performance of the satellite’s scientific instruments.

Rising sea level puts people at risk of flooding

Sea-level rise is one of the most serious consequences of the climate crisis. Since 1993 satellite data show that the global mean sea level has risen, on average, by over three millimeters every year. Over the last ten years the global mean sea level has been increasing at average by even four millimeters per year. While a rise of three millimeters may not sound like a lot, this means that every year the sea rises, on average, another three millimeters. Over thirty years this sums up to a rise of nine centimeters. For every additional centimeter of sea-level rise, an extra three million people are at risk of annual flooding.

Why is the sea level rising?

Climate change is the main cause of rising sea levels. Around 45% of this rise is due to the melting of ice from the Greenland and Antarctic ice sheets, as well as from mountain glaciers. Another major contributor to sea-level rise (account for around a third) is the warmer ocean water due to climate change. This causes thermal expansion, whereby warming seawater increases in volume. 

Why measuring sea-level rise from space?

Due to the enormous size of the oceans, which cover 70% of the Earth, the use of satellites from space is necessary for measuring the rising sea-level. For this purpose, Copernicus Sentinel-6 carries a radar altimeter as a main sensor. The instrument is best suited to observe sea level and ice thickness in the polar regions. In addition, the satellite uses several instruments for navigation and observation of water vapor. Sentinel-6 will map up to 95% of the earth’s ice-free ocean every ten days. 

About Sentinel-6B

The Sentinel-6 mission consists of two identical satellites: Sentinel-6 Michael Frelich, launched in late 2020, and Sentinel-6B, set for launch on Monday. These satellites continue the legacy of sea-surface height monitoring that began in 1992 with the French–US Topex Poseidon mission, followed by the Jason series of satellites. 

Sentinel is part of European earth observation program Copernicus

Sentinel is an important part of Copernicus, the Earth observation component of the European Union’s space program. Copernicus is considered as the world’s most advanced Earth observation system. It provides free Earth observation data and services to organizations and citizens around the globe. Copernicus offers information services that draw from satellite Earth Observation and in-situ (non-space) data. The European Commission manages the program. It is implemented in partnership with the Member States, the European Space Agency, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), the European Centre for Medium-Range Weather Forecasts (ECMWF), European Union Agencies and Mercator Océan, the European Environment Agency, and the Joint Research Center.

More information about the European Union’s Copernicus Earth observation program:
https://www.copernicus.eu/en
https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-6

Images and Video

Image 1: A Beyond Gravity navigation receiver precisely determines the in-orbit-position of Sentinel-6B, contributing to more precise scientific data. © Beyond Gravity. Download: https://www.beyondgravity.com/sites/default/files/styles/stage_mid_x_large/public/media_image/2022-03/Navigation%20receiver_01_color_2.jpg.webp?itok=QU5MMZI1

Image 2: The environmental satellite Sentinel-6B monitors sea-surface height. © ESA/ATG Medialab. Download: 
https://www.esa.int/ESA_Multimedia/Images/2020/09/Copernicus_Sentinel-6_radar_altimeter

Image 3: The Sentinel-6B satellite uses a small but powerful data downlink antenna from Beyond Gravity. © ESA/Beyond Gravity. Download:  https://www.esa.int/ESA_Multimedia/Images/2018/11/Data_downlink_antenna

Image 4: Oliver Grassmann, Executive Vice President Satellites at Beyond Gravity. © Beyond Gravity. Download:
https://www.beyondgravity.com/sites/default/files/styles/gallery_lightbox_x_large/public/media_image/2023-05/Oliver%20Grassmann-029.jpg.webp?itok=2TXVgR0W

Video: Learn how Beyond Gravity is pushing boundaries of what is technically feasible for the benefit of humankind. 

*ESA on the contribution of in-orbit position determination to the overall mission performance: https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-6/Sea-level_monitoring_satellite_first_results_surpass_expectations

More about navigation solutions from Beyond Gravity: https://www.beyondgravity.com/en/satellites/electronic-solutions/navigation-receivers