{"id":3171,"date":"2018-10-12T06:16:55","date_gmt":"2018-10-12T06:16:55","guid":{"rendered":"http:\/\/www.styledeals.co.uk\/blog\/german-satellites-sense-earths-lumps-and-bumps\/"},"modified":"2018-10-12T06:16:55","modified_gmt":"2018-10-12T06:16:55","slug":"german-satellites-sense-earths-lumps-and-bumps","status":"publish","type":"post","link":"https:\/\/www.styledeals.co.uk\/blog\/german-satellites-sense-earths-lumps-and-bumps\/","title":{"rendered":"German satellites sense Earth’s lumps and bumps"},"content":{"rendered":"\n
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\n The map traces the variations in height across the Earth’s land surfaces
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The German space agency (DLR) has released a spectacular 3D map of Earth. <\/strong><\/p>\n

Built from images acquired by two radar satellites, it traces the variations in height across all land surfaces – an area totalling more than 148 million sq km. <\/p>\n

DLR is making the map free and open, enabling any scientist to download and use it. <\/p>\n

There will be myriad applications, from forecasting where flood waters flow to planning big infrastructure projects. <\/p>\n

How was the map made?<\/h2>\n

The two satellites involved are called TerraSAR-X and TanDEM-X. <\/p>\n

Like all radar spacecraft, they send down microwave pulses to the surface of the planet and then time how long the signals take to bounce back. <\/p>\n

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\n The satellites fly close to each other some 500km above the Earth
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The shorter the time interval, the higher the ground. TerraSAR-X and TanDEM-X fly virtually side by side, sometimes coming to within 200m of each other. <\/p>\n

This is complex to control, but it gives the pair “stereo vision”, by allowing them to operate an interferometric mode in which one spacecraft acts as a transmitter\/receiver and the other as a second receiver. <\/p>\n

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\n Tibet in the Himalaya. The images use colour to denote elevation. Red is high; blue is low
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How precise is the map?<\/h2>\n

The resolution of the newly released digital elevation model (DEM) is 90m<\/a>, meaning the land surface has been divided up into squares that are 90m along the side. <\/p>\n

The absolute accuracy in those squares in the vertical dimension is 1m, making the DEM a powerful rendering of all the Earth’s lumps and bumps. <\/p>\n

There are DEMs that have far higher resolution on regional scales, but this new product beats any other global, publicly available dataset. It also has no gaps. <\/p>\n

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Image caption<\/span>
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\n The Sahara desert, showing part of the Tamanrasset province of central Algeria
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What are the next steps?<\/h2>\n

DLR has other versions of the map whose sampling squares are 30m and 12m across, but these are – for the time being – commercially restricted. <\/p>\n

TerraSAR-X and TanDEM-X continue their mapping exercise. <\/p>\n

Having a static DEM is great but the shape of the Earth’s surface is always changing and this needs to be captured as well. <\/p>\n

The orbiting pair are now getting quite old. TerraSAR-X was launched in 2007 and TanDEM-X was launched in 2010. <\/p>\n

DLR hopes to keeping them running for a good few years yet, but planning for the replacements is well advanced.<\/p>\n

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\n The northern Appalachian Mountains in the US state of Pennsylvania
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What comes after these satellites?<\/h2>\n

The future mission would be slightly different in that the radar instruments would operate not in the X-band but in the L-band – a longer wavelength. <\/p>\n

This would facilitate different types of application. “In forests, for example, in the X-band you get, more or less, the top of the canopy,” explained Dr Manfred Zink from DLR’s Microwaves and Radar Institute<\/a>. <\/p>\n

“You don’t penetrate and see under the leaves. But with the L-band we will penetrate; we will see the solid ground. That would enable us to see the vegetation volume in real 3D. It’s tomography,” he told BBC News. <\/p>\n

“We would see the full vertical structure of the forest and that is key for precise biomass estimates.” <\/p>\n

Knowing exactly how much carbon is tied up in the world’s forests is a big unknown, but vital for climate change assessments. <\/p>\n

Another application in the L-band would be to sense better the way the ground deforms during an earthquake. <\/p>\n

Scientists do this already using radar satellites operating at other wavelengths, but their observations can often be difficult to interpret in places where there is a lot of vegetation growth. <\/p>\n

TanDEM-L, as the future system will be known, would hope to get around some of these difficulties.<\/p>\n

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\"AntarcticImage copyright<\/span>
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\n Glaciers flow towards the Weddell Sea on the eastern side of the Antarctic Peninsula
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Jonathan.Amos-INTERNET@bbc.co.uk<\/span><\/a> and follow me on Twitter: @BBCAmos<\/a><\/p>\n<\/p><\/div>\n