从太空探测万里长城

Detecting the Great Wall from space

2004年 5月 11日,欧空局网站发布了题为“从太空看长城”的公告,引起广泛关注和热烈争论.争论焦点涉及如何正确认识人眼视觉原理,如何准确理解卫星遥感应用潜力等问题.文章从人眼结构、产生光觉、视觉和形觉的基本条件以及眼睛分辨率等基本概念入手,判定肉眼从太空不可能看到长城.同时通过理论分析与实验,揭示了空间分辨率达到米级的SPOT-5全色图像能够清楚地展现北京密云水库北面的各段野长城.在分辨率为 10m和 20m的多光谱图像上,无法辨别出长城.而在全色(2. 5m, 5m)与多光谱进行融合处理的图像上,各段野长城及其周围背景都能十分清晰地显示出来.

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.