Space Technology Facilitates the Preventive Monitoring and Preservation of the Great Wall of the Ming Dynasty: A Comparative Study of the Qingtongxia and Zhangjiakou Sections in China

In this study, an integrated monitoring and evaluation approach was proposed to fix the systematic safeguarding gap of the Great Wall corridor using space technologies. Two representative sections of the Great Wall located in Qingtongxia County and Zhangjiakou City in China were selected for a preliminary comparative investigation to ascertain the coupling mechanism and spatiotemporal characteristics of the driving forces for the heritage damage. The surface deformation rates were estimated by synthetic aperture radar interferometry, and the interaction between the deformation rates and the normalized difference vegetation index (NDVI) and meteorological and topographic data was calculated using the correlation matrix. The results showed the following: 1) the surface motions along the observed landscape corridor of the Great Wall were decreased in 2015-2018; 2) the correlation coefficients between the deformation rate and the elevation, slope, annual wind speed, and NDVI in Qingtongxia were 0.524, 0.115, 0.582, and 0.522, respectively, indicating the dominant influence of surface runoff and high winds on the degradation of the rammed-earth wall in the western arid regions; vice versa, 3) the correlation coefficients between the deformation rate and the aforementioned factors in Zhangjiakou were 0.065, 0.027, 0.025, and 0.052, respectively, indicating negligible effects of natural processes for the decline of Great Wall in the eastern section. This study not only provides new insights into preventive monitoring and risk assessment of the entire Great Wall but also highlights the potential of space technologies and a geographical perspective for the sustainable conservation of large-scale heritage sites.