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Night-Time Light Imagery Reveals China's City Activity During the COVID-19 Pandemic Period in Early 2020

The COVID-19 global pandemic has posed a serious impact on human life and health. Facing this unknown, unexpected, and devastating disease, China launched a resolute battle to prevent and control its spread. This study focused on assessing the recovery of city activity of 17 administrative regions in China around the COVID-19 pandemic period in early 2020. The night-time light (NTL) satellite remote sensing data, NPP-VIIRS dataset, was applied to evaluate the NTL changes during the coronavirus epidemic to understand the impact of the epidemic on city activity and the economy of China. A series of median composites was first constructed to analyze short-term NTL changes. Based on these median composites, the ratio map, difference map, wave index, and recovery ratio (RR) were defined to indicate the NTL recovery pattern and its spatial distribution characteristics. The results are as follows:first, the adopted median composites are able to describe the NTL changes in the short term; second, the recovery of city activity could not be exactly described by RR of a single year but could be evaluated by the comparison of RR between two adjacent years; third, a partial and spatially heterogeneous recovery of city activity is observed after the 2020 holiday compared to 2019, fourth, a better degree of recovery is observed after China announced its fully work resumption.