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ABSTRACT
Night-time light (NTL) data shows a high correspondence with human activities. Recent studies also found that the NTL responds to holidays, and that light values often peak at festival times. However, there are few studies on the different patterns of light change caused by different cultural events. Here, we examined the impacts of festivals on NTL, examining both the seasonal changes in NTL, and the spatial patterns of NTL changes during festivals. The monthly Visual Near-Infrared band composites on Suomi National Polar-orbiting Partnership (Suomi NPP VIIRS) from January 2014 to December 2017 were used. Firstly, we studied two religious events, Ramadan in Mecca, Saudi Arabia, and Ashura in Najaf, Iraq. We extracted the seasonal changes using a Seasonal-Trend decomposition procedure based on Loess and a proposed Information Ratio (IR) index, and found two completely different light change patterns, which corresponded to two Islamic factions, Shia and Sunni. Secondly, we studied two kinds of celebrations, Carnival and a catholic religious event (Day of the Virgin of Guadalupe), in Cancún and Puebla City in Mexico and found the distribution of light change during festivals is clearly distinguished between carnival and the religious event. The NTL during Carnival increases uniformly throughout the city, while the NTL during religious event presented an aggregate increase centring on the central cathedral. Thirdly, we calculated the Information Ratio (IR) values at the pixel scale and analysed the spatial distribution of seasonality in the four regions, Mecca and Najaf showing different patterns of light change during the event months compared to Mexico areas. The analysis shows that different characteristics of different cultures can be distinguished through the spatio-temporal analysis of NTL data. Given the responses of NTL to cultural context, local knowledge should be incorporated to better understand how people modify the nightscape.