Remote Sensing of Cultural Heritage Sites

The Great Wall of China (2/2)

Contribution of Remote Sensing

In 2006, the State Administration of Cultural Heritage and the State Bureau of Surveying and Mapping in China launched the joint China's Great Wall Protection Project.

This Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sub-image covers a 12 x 12 km (7.5 x 7.5 miles) area in Northern Shanxi Province, China, and was acquired January 9, 2001. The low sun angle, and light snow cover highlight a section of the Great Wall, visible as a black line running diagonally through the image from lower left to upper right.
Source: NASA

The objectives of the project are to provide basic information about the Great Wall, to develop protection plans, to add funds for the protection of the Great Wall and to repair damages. Research within the project is based on technologies such as infrared range finders, remote sensing technology, geographic information systems and a global positioning system.

In April 2009, when Phase I came to an end, experts announced that new portions of the wall that stretch from Hu Mountain in northern Liaoning province to Jiayu Pass in western Gansu province had been discovered. The presently known length of the Ming dynasty Great Wall was found to be 8,851.8 km.

The joint project will continue until 2010. Further plans include the mapping of sections of the wall built during the Qin (221 B.C.-206 B.C.) and Han (206 B.C.-9 A.D.) dynasties.

These radar images show two segments of the Great Wall of China in a desert region of north-central China, about 700 kilometers (434 miles) west of Beijing. The wall appears as a thin orange band, running from the top to the bottom of the left image, and from the middle upper-left to the lower-right of the right image. These segments of the Great Wall were constructed in the 15th century, during the Ming Dynasty. The wall is between 5 and 8 meters high (16 to 26 feet) in these areas. The entire wall is about 3,000 kilometers (1,864 miles) long and about 150 kilometers (93 miles) of the wall appear in these two images. The wall is easily detected from space by radar because its steep, smooth sides provide a prominent surface for reflection of the radar beam. Near the center of the left image, two dry lake beds have been developed for salt extraction. Rectangular patterns in both images indicate agricultural development, primarily wheat fields.
Source: NASA / JPL

Another result of the China's Great Wall Protection Project is that this World Heritage site is under great threat, mainly because of climate change and the country's massive infrastructure development.

The western section of the wall, for the most part located in the desert, has traditionally been built with sand and mud, making it vulnerable to erosion caused by extreme weather conditions such as wind storms. The frequency of such storms is increasing as a result of climate change. Erosion of the wall is most obvious in the Ning Xia region.