This animation shows the radar pulse of the altimeter of the Michael Freilich satellite Sentinel-6 bouncing off the surface of the sea to measure the height of the ocean. Photo credit: NASA / JPL-Caltech
The spaceship Sentinel-6 Michael Freilich will soon be launched into orbit to monitor the height of the ocean for almost the entire globe.
Preparations for the launch of the world’s newest sea level satellite on November 10 are in full swing. Since arriving in a giant cargo plane at Vandenberg Air Force Base, California last month, Sentinel-6 Michael Freilich has performed final checks, including visual inspections, to ensure it is fit for orbit.
Surviving the bone-rattling vibrations and launch sounds on a Falcon 9 missile is just the beginning of the mission. As soon as Sentinel-6 Michael Freilich is in an orbit 1,336 kilometers above the earth, he has the task of taking sea level measurements with one accuracy of a few centimeters (for a single measurement) for more than 90% of the world’s oceans. And it will take these measurements as it flies repeatedly through an area of intense radiation known as the South Atlantic Anomaly, which can mess up electronics.
The Michael Freilich Sentinel-6 satellite is being prepared for launch in early November in a clean room at Vandenberg Air Force Base, California. Photo credit: ESA / Bill Simpson
For this reason, engineers and researchers Sentinel-6 Michael Freilich subjected a series of tests to ensure that the spaceship would survive the launch and the harsh environment of space. But how will the mission do the rest? With sophisticated instruments, global navigation satellites and lasers – lots of lasers. They will all work together so that the spaceship can do its job of observing the ocean.
Given the challenges and objectives of the mission, the satellite’s nickname is appropriate: it is named after famous researcher Dr. Michael Freilich, the former director of NASADepartment of Earth Sciences.
A second spaceship, identical to Sentinel-6 Michael Freilich, Sentinel-6B, will launch in 2025 to continue work after the end of its siblings’ five and a half year main mission. Together, the satellites form the Sentinel-6 / Jason-CS (Continuity of Service) mission, a partnership between NASA, ESA (European Space Agency), the European Organization for the Use of Meteorological Satellites (EUMETSAT) and the National Oceanic and Atmospheric Administration ( NOAA).
Taken together, the satellites will add the most accurate satellite elevation data to date to a nearly 30-year record that documents how our oceans rise in response to climate change by a decade. Both spacecraft will also collect data on air temperature and humidity that will help improve weather forecasting and atmospheric and climate models.
This is where these sophisticated instruments, global navigation satellites and lasers come into play.
How it works
In order to accurately measure extremely small fluctuations in sea level, Sentinel-6 Michael Freilich will use a number of three instruments that provide scientists with information to determine the precise position of the spacecraft in orbit.
One component of this positioning kit is the laser retroreflector array, a set of nine small, precisely shaped mirrors. Lasers are aimed at them from ground stations on earth and reflect the (harmless) rays back to their place of origin. These so called laser emitting range stations calculate how long it takes for the laser to bounce off the reflectors and return, which is the distance between the satellite and the station.
Another instrument, the Global Navigation Satellite System – Precise Orbit Determination (GNSS-POD), tracks GPS and Galileo navigation signals. The researchers analyze these signals to determine the position of the satellite.
The third instrument in the positioning package is Doppler Orbitography and X-ray Positioning (DORIS) integrated by satellites. It analyzes radio signals from 55 global ground stations and measures the Doppler shift of the frequencies of the radio signals in order to determine the 3D position of the satellite over time. Together, these instruments provide the data needed to determine the exact position of the satellite, which in turn helps determine the elevation of the sea surface.
On the scientific side, there are two instruments that work together to determine sea level and a third that collects atmospheric data. The Poseidon 4 radar altimeter measures sea level by bouncing radar pulses off the surface of the water and calculating the time it takes for the signal to return to the satellite. However, water vapor in the atmosphere affects the propagation of radar pulses from the altimeter, which can make the ocean appear higher or lower than it actually is. To correct this effect, an instrument called the Advanced Microwave Radiometer for Climate (AMR-C) measures the amount of water vapor between the spacecraft and the ocean.
“AMR-C is the next generation of AMR instruments and includes new components that allow more accurate measurements along the coast and throughout the mission,” said Shannon Statham, AMR-C integration and test manager at NASA’s Jet Propulsion Laboratory in Southern California.
Our planet is changing. Our ocean is rising. And it affects us all. Because of this, a new international satellite will continue the decades-long monitoring of our global ocean and help us better understand how climate change is changing our planet.
For information on the atmosphere, the Global Navigation Satellite System – Radio Occultation (GNSS-RO) instrument collects data on temperature and humidity that can help improve the weather forecast. GNSS-RO analyzes radio signals from global navigation satellites as they appear and disappear beyond Earth – the hazy blue edge of the atmosphere visible when you look at images of our planet in space. As these radio signals travel through different layers of the atmosphere, they flex and slow down to varying degrees. Sentinel-6 Michael Freilich and similar satellites use GNSS-RO technology to measure these changes. Researchers can extract atmospheric properties such as temperature and humidity at different altitudes.
All instruments, power systems, and telecommunications companies – anything that makes Sentinel-6 Michael Freilich tick – must work together to achieve the mission’s scientific goals, just as the international partners worked together to prepare this satellite for launch.
“Copernicus Sentinel-6 Michael Freilich makes a major contribution to climate change, environmental monitoring and the digital twin earth. Sentinel-6 is a reference model for cooperation between the USA and Europe in earth observation and represents a good basis for future projects, ”said Josef Aschbacher, ESA Director for Earth Observation Programs.
In this illustration, the spaceship Sentinel-6 Michael Freilich – the world’s newest satellite at sea level – orbits the earth with its solar modules extended. Photo credit: NASA / JPL-Caltech
More about the mission
Sentinel-6 / Jason-CS is being developed by ESA, EUMETSAT, NASA and NOAA with financial support from the European Commission and technical support from the French National Center for Space Studies (CNES).
JPL, a division of Caltech in Pasadena, supplies three scientific instruments for each Sentinel-6 satellite: the Advanced Microwave Radiometer, the Global Navigation Satellite System – Radio Occultation, and the Laser Retroreflector Array. NASA also contributes to launch services, ground systems that aid the operation of NASA’s scientific instruments, the scientific data processors for two of these instruments, and to support the international ocean surface topography science team.
