Space radar reveals secrets of Great Wall
Saturday 20 April 1996
The pictures can identify different versions of the wall - one of the few manmade structures visible with the naked eye from space. It was first built in the third century BC, to protect the country from northern invaders.
"In the images, we can recognise two different dynasties that built the Great Wall," said Dr Guo Huadong, of the Chinese Academy of Sciences in Peking. "One was built in the Ming dynasty and is about 600 years old. The other was built during the Sui dynasty and is more than 1,000 years old."
The colour picture (top right) shows a 45-mile segment of the wall, which in total is more than 1,860 miles long. This piece lies about 430 miles west of Peking, in a remote part of the north-central China desert, and is visible running from top to bottom as a continuous line.
The radar images are black and white, each showing a section two miles long. The one illustrated here shows the two generations of construction: the bright line on the left is the present-day wall, while just to its right is a discontinuous line - the part built during the Sui dynasty (which lasted from 589-618), which has been intermittently buried by sand dunes blown by winds.
"In this region the wall was made out of loose soil and mud, not bricks and rocks," Dr Huadong said. "Usually you cannot find these segments even if you go there, so the radar data are helping to show us the whole wall."
The different generations of the wall are easy to detect by radar from space, because the steep, smooth sides - between 15 and 25 feet high in its present form - provide a prominent surface which reflects the radar beam.
The radar, called the "synthetic aperture radar", was carried on the Space Shuttle and took these pictures earlier this year.
"Archaeology wasn't one of our original science objectives, but the imaging radar data has been found to be very useful for this type of research," said Dr Diane Evans, a project scientist at the United States space agency, NASA.
The radar system is now being used for archaeological efforts in areas which include Angkor in Cambodia, the Lost City of Ubar, in Oman, and the Silk Road along the north-west desert of China.
- 1 Nigel Farage: Me vs Russell Brand on Question Time – he's got the chest hair but where are his ideas?
- 2 Harry Potter fans can apply to the Hogwarts-inspired College of Wizardry
- 3 Jessica Chambers: 19-year-old woman 'doused with lighter fluid and burned alive' in the US
- 4 Russell Brand calls Nigel Farage 'poundshop Enoch Powell' in BBC Question Time debate
- 5 Orange Wednesdays are no more
Weather bomb in pictures: Storms cuts power for tens of thousands – and snow is on the way
Jessica Chambers: 19-year-old woman 'doused with lighter fluid and burned alive' in the US
Russell Brand calls Nigel Farage 'poundshop Enoch Powell' in BBC Question Time debate
Russell Brand was rendered speechless on Question Time by this man
Fury at Airbus after it hints the super-jumbo may be mothballed
Disgruntled RBS worker writes hilarious open letter to Russell Brand after anti-capitalist publicity stunt leaves him hungry
Nigel Farage defends Kerry Smith 'ch***y' comment: 'If you are going for a Chinese, what do you say you’re going for?'
Nigel Farage's approval rating hits 'record low' as popularity suffers in wake of Ukip sex scandal
Pakistan school attack live: Taliban kill at least 132 children in 'horrifying' massacre
Sony hack: Angelina Jolie branded 'seriously out of her mind' in further embarrassing leaked email saga
Panic Saturday: 13 million Britons spend £1.2bn – while 13 million others across the country live in poverty unable to afford food
£30000 - £35000 per annum: Recruitment Genius: An opportunity has arisen for a...
£30000 - £35000 per annum: Recruitment Genius: An exciting opportunity to join...
£30000 - £35000 per annum: Recruitment Genius: We have an excellent role for a...
Negotiable: Recruitment Genius: An IT Support Analyst is required to join the ...