Analyzing Nighttime Lights Using Multi-Temporal Imagery from Luojia-1 and the International Space Station with In Situ and Land Use Data

Remotely sensed nighttime lights (NTLs) have become essential in urban and environmental research but are typically captured at fixed local times by sun-synchronous satellites, limiting their ability to capture changes throughout the night. In contrast, in situ measurements of night sky brightness (NSB) can provide continuous records over time, but direct comparisons with NTLs have remained rare. This study first examines the relationship between in situ NSB and remotely sensed NTLs using multi-temporal imagery from Luojia-1 and the International Space Station (ISS), focusing on 10 sites in Hong Kong and Macau. We find moderate to strong correlations between NSB and Luojia-1 (R = 0.73) and between NSB and ISS imagery (R = 0.8–1.0), though notable spatial and temporal variations persist. Even images captured within seconds differ in brightness across locations (R = 0.88–0.96), driven by factors such as changing viewing angles in dense urban areas, variations in light transmission paths, and atmospheric conditions, all influenced by satellite position. Our further analysis reveals distinct temporal patterns across land use categories: port facilities and airports are brightest late at night, whereas commercial districts peak earlier and gradually dim throughout the night. Within individual ISS images, transportation-related lighting tends to be red, and commercial areas appear blue compared to other urban areas, which may be due to lamp type differences (high pressure sodium, LED). This study highlights the need to cross-examine in situ and remotely sensed data in NTL research, emphasizing that factors such as local pass time, viewing geometry, color sensitivity, and atmospheric conditions can influence observations and ultimately affect the conclusions.