Fig. 15. The NTL change maps, the time series plot of a selected pixel, and high-resolution images for Raqqa, Syria. (a) The accumulated annual NTL change maps from 2013 to 2021 with the latest detected change year presented. (b) The day-of-year NTL change map in 2015 over the region enlarged from the white rectangle from Fig. 15a. (c) The time series plot of a selected pixel (red cross in Fig. 15b) and the corresponding VZA-COLD detection results, in which the red, green, blue, and grey colors indicate the different VZA intervals, lines represent the estimated models, small dots are the DNB observation, and the large magenta dots are the detected changes. (d) The high-resolution Google Earth image in January 2013. The red rectangle represents the location and size of the selected pixel. (e) The high-resolution Google Earth image in July 2020. The red rectangle represents the location and size of the selected pixel. The dark background in Fig. 15a and Fig. 15b is the Esri ArcMap Dark Gray Canvas base map.