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DTU on high-precision climate mission in space

Posted May 22, 2018

NASA will soon be launching the comprehensive climate mission GRACE Follow-On (GRACE-FO). The launch is scheduled from Vandenberg Air Force Base in California with a SpaceX Falcon 9 rocket.

The mission comprises two satellites, which in the coming years and with great precision will examine the hydrological cycle and thus the Earth’s climate. Among other things, the satellites will be used to monitor the melting of the land ice in the Arctic and Antarctica, sea water levels and the distribution of groundwater. DTU Space has developed technology for the satellites, and is involved in the climate research, which is the purpose of the mission.

“The movement of water, whether it is rainwater, groundwater, seawater, or melted ice, is an important parameter in the climate system. With GRACE-FO, we can achieve long, continuous and very accurate measurements of the changes on our planet, and thus obtain a more accurate picture of the climate changes taking place and their effect,” says Professor and Head of Measurement and Instrumentation John Leif Jørgensen from DTU Space.

The measurements are made by the two satellites in partnership recording small changes in gravity. The drag the Earth exerts on the satellites as they orbit the planet depends on the local mass concentration. This concentration changes when ice melts, water levels increase in the oceans, or when groundwater reservoirs grow or decrease. In this way, it is possible to calculate to a high degree of accuracy how much ice is melting or how much global sea levels are rising.

Builds on unique concept
GRACE-FO builds on the unique work that began with the design and construction of the GRACE 1 and GRACE 2 satellites 20 years ago as part of a collaboration between Airbus, NASA’s Jet Propulsion Laboratory (JLP), and DTU Space. This successful mission was launched in 2001 and completed last year. Here, Danish, German, and US researchers cooperated on mapping with great precision the climate changes taking place.

Now take GRACE-FO is taking over where GRACE left off. But with even greater precision in measuring the condition of the Earth’s climate.

This type of satellite is unique, as they are the only satellites that can measure changes in mass concentration on Earth. The highly sensitive satellite system can actually measure so accurately that it can detect whether it has rained in central London, for example. Other climate satellites, such as the European Sentinel satellites, typically measure differences in altitude.

However, the mass concentration measurements conducted with the GRACE satellites have provided the same results as altitude measurements made with other types of systems. With the two independent types of measuring, today there is a relatively solid body of knowledge about the climate changes which are taking place at the moment. And it is this development and its consequences that we must continue to follow and research using data from the new and more precise GRACE-FO satellites.

Precision down to 1/10,000 of a hair’s breadth
The two satellites are flying at a distance of approx. 100 km between them. It is by measuring the variations in the distance between the two satellites which occur as a result of gravity differences beneath them that data on changes in the quantity of, for example, ice and groundwater, and therefore climate change, are obtained.

The distance between the GRACE-FO satellites is measured, for example, by using laser light, whereas the previous GRACE mission used microwaves which is not quite as precise a technology.

Where the previous GRACE mission could measure variations in the distance between the two satellites down to 1/100 of a hair’s breadth, the new GRACE-FO satellites work by achieving a precision of 1/10,000 of a hair’s breadth. This is roughly the diameter of an atom. Thus, this will enable an unprecedented degree of precision in the task of mapping climate change from space.

DTU Space has developed the star trackers which the satellites use for positioning.

“It has been a big challenge, as it must be done with much higher precision than before,” says John Leif Jørgensen.

“The previous satellite missions have given us a clear picture of how the climate is changing. With the new GRACE-FO satellites, we will obtain even better data to work with in future in the form of much higher spatial resolution than from the original GRACE mission, so that you can see even smaller signals. Not least, GRACE-FO will extend the 15-year time series of data to climate studies first started by GRACE,” says Ole Baltazar Andersen, Senior Researcher at DTU Space.

Source: DTU

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