In October, Earth observation satellite Jason-3 will officially take over duties from its predecessor. Weather services and researchers worldwide will then be able to determine the sea level much more precisely.
Image: NASA.gov
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Discovering the secrets of our planet
Earth observation satellites can help us understand planet Earth better. They can do much more than just predicting the weather - an overview
Image: NASA.gov
Measuring the sea level
Jason-3 was launched on January 17th, 2016. It took over from Jason-2 in October of that year. The satellite became part of a large Network of NASA satellites, looking at sea Levels and at oceanic and atmospheric currents.
Image: NASA.gov
Is the sea level rising, or is the continent sinking?
Level recorders installed at shore can't answer that question. However, satellites can recognize continental shift. That's why NASA launched its Ocean Surface Topography Mission (OSTM) using the satellites Topex/Poseidon, Jason-1, -2 and later -3 to solve the mystery. Jason-2 sent us topographical radar images, and its successor Jason-3 has additional tools on board -- a radiometer and a laser.
Image: NASA.gov
Lots of data for environment and development
Without Earth observation satellites, we would not understand our planet as well as we do now. Sentinel-2 took this picture of the northern shore of the Adriatic with the Italian Alps in late June, shortly after its launch. Sentinel-2 is part of the European Space Agency's (ESA) comprehensive Copernicus Earth observation program.
Image: Copernicus data/ESA
Small box, great camera
Sentinel-2 uses a spectrometer, which is a special camera that can take pictures at numerous light wavelengths. This enables scientists to see all kinds of details in pictures that you can't detect with the naked eye, including the status of vegetation or the moisture in the soil. Here, engineers are preparing the satellite for its journey.
Image: picture-alliance/dpa/P. Kneffel
What grows where and how well?
A view of Northern Italy: The city of Pavia in the upper left corner with the river Ticino flowing into the larger Po. The infrared spectrum of the camera reveals the state of the agriculture: Scientists can even see what is growing on the fields - is it corn, wheat or pumpkins on this one?
Image: Copernicus data/ESA
Twins for better observation
Many Earth observation satellites are not alone in their mission; they do their job better as a team. This is also true for Sentinel-1 and -2, which eventually will each get a support satellite. Together they can document every spot on the surface of the planet every five days. The Copernicus Program includes six modules (Sentinel-1 through -6) for all kinds of tasks.
Image: ESA/ATG medialab
Radar for topography
One task is measuring the topography of the land, just as Jason-3 does with the sea. Sentinel-1 is built for that, with its large radar antennas. It can detect hills, mountains and valleys. The data the satellite generates can later be combined with the data from Sentinel-2 or other satellites. This gives farmers, developers and environmental agencies exactly the information they need.
Image: ESA/ATG medialab
The Netherlands are all but flat.
The radar-eye of the satellite took this picture of the Dutch coast. It shows that the country is not as flat as many may believe. Dunes, buildings and levees can be clearly seen.
Image: ESA
Its not just, what's on the surface…
ESA's SWARM mission is a whole different type of Earth observation: Three satellites are circling the Earth, looking deep into the core of the planet. The SWARM satellites have been recording changes in the magnetic field of the Earth since 2013.
Image: Astrium/picture-alliance/dpa
Changes you cannot see
Scientists are interested in the Earth's magnetic field because it is constantly changing. Under the Earth's crust, magma is constantly moving and changing the magnetic makeup. Even the magnetic poles sometimes swap places. Knowing this is extremely important for the sea and air navigation.
Image: GFZ
Observing Earth with the Sun in mind
Earth magnetism also affects our relationship to the sun. The magnetic field shields us against cosmic and sun rays, which can be particularly strong after sunspot eruptions. If the Earth's magnetism changes, it also changes the way particles from solar rays travel around the Earth's poles. Satellites looking toward Earth can sometimes reveal these secrets from far away.
Image: picture-alliance/dpa
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Climate scientists, weather services and coastal protection officials need to now how high sea levels across the world really are. But it's pretty hard to determine the precise movement of waves and the depth of the water accurately. Sea levels are being influenced by so many factors that they are hard to grasp.
They are influenced by the position of celestial objects - most noticeably the moon, which is responsible for high and low tides. Wind, volcanic or seismic activities, movements of tectonic plates, earthquakes and even more simple factors like rain and snow or freezing sea ice in the polar regions can all influence sea levels as well.
To make matters more complicated, scientists also have to deal with the fact that Earth isn't really round. When you look at its gravitational field, you will see it's shaped more like a potato than a perfect ball. And even the gravitational patterns may change over time, triggered by movements deep under the Earth's surface.
The "gravity potatoe" of the German Research Centre for Geosciences (GFZ) shows how uneven the distribution of gravity isImage: GFZ
"Normal zero" isn't normal
Furthermore, the Earth's rotation also has an effect on the sea level. The result: it does not have the same distance from the geocenter, everywhere. For example at the equator, the ocean surface is more than 4,700 meters farther away from the planet's center than at the 30th degree of northern latitude. This means that the highest mountain on earth is actually not Mount Everest - when calculating its distance from the geocenter.
The peak of the Chimborazo in Ecuador is 6,384,557 meters above the center of the Earth, while the peak of Mount Everest stands only 6,382,414 meters tall. However, when looking at height from the ocean surface - which is the traditional way of measuring mountains - Mount Everest with its 8,848 meters stands higher than the 6,267 meter tall Chimborazo, of course.
Satellites can handle gravitational influences very well by calibrating the data through computing. They are virtually immune against earthly factors such as tectonic movements or weather since they're running on rather stable orbits and are therefore incorruptible.
The newest satellite for measuring the ocean surface is Jason-3 - a joint project of the US space agency NASA and its French counterpart CNES. The US weather service NOAA and the European Meteorological satellite service Eumetsat are also involved in the project.
A complete picture once every ten days
Jason-3 circles Earth at 1,330 kilometers and is scanning 95 percent of the ice-free ocean surface every ten days. The precision of the measurements reaches up to four centimeters - considerably less than normal waves generate.
To ensure that the orbit of the satellite is known and that the collected data is correct, Jason-3 uses three different instruments to determine its own orbit down to a centimeter: the satellite navigation system GPS, an instrument called the "Doppler Orbitography and Radiopositioning Integrated by Satellite" (DORIS) and a Laser Retroflector Array which can measure the altitude of the satellite.
Jason-3 was launched on January 17. Now it is operational.Image: picture-alliance/dpa/Nasa
Early detection of tropical storms
The satellite is also able to measure water temperature. This way it can identify pools of warm water from which tropical storms such as typhoons or hurricanes can develop. And the quality of the reflected radar signals gives meteorologists information about wind speeds and the height of waves.
Jason-3 was launched on 17 January from the Vandenberg Airforce Base near Lompoc, California. NASA has passed the satellite control over to NOAA on 3 June after a six-month installation period. Since then, the meteorologists have been able to compare and calibrate the data that Jason-3 delivers with that from the predecessor satellite Jason-2.
Learn more at a life-briefing
In early October Jason-3 is supposed to take over his new role as the official "source of reference for global measurements of the sea level from space." Then, weather services worldwide will be able to use the data.
And for everybody who wants to learn more about Jason-3, there is an interactive opportunity: On September 19th starting at 16:00 Central European daylight savings time, Eumetsat is organizing a life-briefing, here - and on twitter: #askjason3.
