October 15th, 2020 by Steve Hanley
The Sentinel-6 Michael Freilich satellite has arrived at Vandenberg in southern California after a two day trip across the Atlantic and the US from Munich, Germany. The satellite will be loaded atop a SpaceX Falcon 9 rocket that will carry it into orbit 830 miles above the Earth on November 10. The satellite is the latest in a long line of instruments that have measured the world’s oceans beginning with the joint U.S.-European TOPEX/Poseidon project in 1992. The Sentinel 6 will be capable of monitoring the level of 90% of the world’s oceans with millimeter accuracy, contributing greatly to the historical record begun by TOPEX/Poseiden and providing Earth scientists with the most up to date and authoritative information available about the oceans of the world along with data about the temperature and moisture content of the atmosphere.
The Sentinel-6 is the product of an historic U.S.-European partnership between NASA and the European Space Agency. It is named for Michael Freilich, the former director of NASA’s Earth Science Division and a tireless advocate for advancing satellite measurements of the ocean. It will continue the work of the Jason 1, 2, and 3 satellites, the last of which was placed into orbit in 2016.
“This continuous record of observations is essential for tracking sea level rise and understanding the factors that contribute to it,” says Karen St. Germain, director of NASA’s Earth Science Division. “With Sentinel-6 Michael Freilich, we ensure those measurements advance both in number and in precision. This mission honors an exceptional scientist and leader, and it will continue Mike’s legacy of advances in ocean studies.” She adds, “The Sentinel-6 Michael Freilich satellite will extend our observation record of global sea level, 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 level.”
According to NASA, the Earth’s oceans and atmosphere are inextricably connected. The sea absorbs more than 90% of the heat trapped by rising greenhouse gases, which causes seawater to expand. This expansion accounts for about a third of modern sea level rise while melt water from glaciers and ice sheets accounts for the rest. The rate of sea level rise has accelerated over the past two decades and scientists expect it to speed up more in the years to come. The rise will change coastlines and increase flooding from tides and storms. The Sentinel-6 satellite will help provide the data need to measure both the extent and rate of change of rising sea levels.
“Sentinel-6 Michael Freilich is a milestone for sea level measurements,” says project scientist Josh Willis of NASA’s Jet Propulsion Laboratory, which manages NASA’s contributions to the mission. “It’s the first time we’ve been able to develop multiple satellites that span a complete decade, recognizing that climate change and rising seas are here to stay.” A twin to the Sentinel-6 satellite is expected to launch, known as Sentinel-6B, is scheduled to launch in 2025. The ESA is developing the new Sentinel family of missions to support the operational needs of the EU’s Copernicus program, the Earth observation program managed by the European Commission.
“It has been a long journey of planning, development, and testing for the mission team,” said Pierrik Vuilleumier, the mission’s project manager at ESA. “We are proud to work with our international partners on such a critical mission for sea level studies and are looking forward to many years of Sentinel-6 Michael Freilich taking critical sea level and atmospheric data from orbit.” Although Sentinel-6 Michael Freilich has already undergone rigorous testing, it will go through a final checkout at the SpaceX payload processing facility at Vandenberg to verify that the satellite is functioning correctly and is ready for launch.
Prior satellites have been very good at measuring large ocean features such as the Gulf Stream but have had difficulty measuring small sea level variations near coastlines. Sentinel-6 Michael Freilich will collect measurements at higher resolution and will include new technology — an Advanced Microwave Radiometer instrument that, in combination with a Poseidon-4 radar altimeter, will enable researchers to see smaller, more complicated ocean features that occur near coastlines.
The European Organisation for the Exploitation of Meteorological Satellites will operate the satellite. Paul Counet, its strategy chief, tells Bloomberg: “Measurements of global and regional sea level have become a valuable tool for decision makers to assess one of the most compelling impacts of climate change and how to prepare for flooding of coastal areas.”
Climate change doesn’t just affect Earth’s oceans and surface, It impacts all levels of the atmosphere, from the troposphere to the stratosphere. An instrument on Sentinel-6 Michael Freilich uses a technique called radio occultation to measure the physical properties of Earth’s atmosphere. It is called the Global Navigation Satellite System – Radio Occultation and it tracks radio signals from navigation satellites that orbit Earth. When a satellite dips below or rises above the horizon from Sentinel-6 Michael Freilich’s perspective, its radio signal passes through the atmosphere. As it does so, the signal slows, its frequency changes, and its path bends. This refraction effect can be used by scientists to measure minute changes in atmospheric density, temperature, and moisture content.
When researchers add this information to existing data from similar instruments currently in space, they’ll be able to better understand how Earth’s climate is changing over time. “Like the long-term measurements of sea level, we also need long term measurements of our changing atmosphere to better understand the full impacts of climate change,” said Chi Ao, the GNSS-RO instrument scientist at JPL. “Radio occultation is a wonderfully precise and accurate way to do that.”
The satellite’s radar altimeter will collect measurements of sea surface conditions, including significant wave heights, and data collected by the GNSS-RO instrument will complement existing observations of the atmosphere. These combined measurements will help meteorologists improve weather forecasts. In addition, information on the temperature and humidity of the atmosphere, as well as the temperature of the upper layer of the ocean, will help to improve models that track the formation and evolution of hurricanes.
JPL, a division of Caltech in Pasadena, is contributing three science instruments for each Sentinel-6 satellite — the Advanced Microwave Radiometer, the Global Navigation Satellite System – Radio Occultation, and the Laser Retroreflector Array. NASA is also contributing launch services, ground systems supporting operation of the NASA science instruments, the science data processors for two of these instruments, and support for the international Ocean Surface Topography Science Team. NASA contracted with SpaceX to launch the satellite. ]
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