Detecting the Great Wall from space

On May 11, 2004, European Space Agency(ESA) issued a bulletin titled Look at the Great Wall from Space, which brought great attention and dispute. The dispute focuses on how to correctly realize the visual principle of human eyes, and how to understand the application potential of satellite remote sensing and so on. This paper, on the basis of analyzing the structure of eyes, the resolving power of eyes and the basic condition creating sense of light, vision and pattern in eyes, proved that the bare eyes of human can't see the Great Wall from space. And also it can be known from our theoretical analysis and experiment that the segments of Great Wall to the north of Miyun reservoir display clearly in SPOT-5 panchromatic image with spacial resolution of 2.5m and 5m. The Great Wall can′t be seen in SPOT-5 multi-spectral image with spacial resolution of 10m and 20m. But the fusion image of multi-spectral and panchromatic shows the Great Wall and the relief around it very clearly.