Spatial heterogeneity of uncertainties in daily satellite nighttime light time series

Abstract

Remotely sensed light imagery provides a unique perspective for high-frequency human activity monitoring. NASA has developed the Black Marble, a daily nighttime light (NTL) product from the Visible Infrared Imaging Radiometer Suite (VIIRS) nighttime images by correcting environmental effects (i.e., atmospheric, lunar, and stray light effects). However, variation and uncertainty remain in the daily lunar-BRDF corrected NTL product and hinder its quantitative applications. To better understand the uncertainty across multiple spatial and temporal scales, this study proposed a spatial–temporal hierarchical analysis strategy to separate uncertainties from different sources, and evaluated the effects of multiple factors on daily NTL time series. The experiments conducted on two populous regions show that: (1) The daily NTL in Northern America has variations up to 50% of the annual average, which is stronger than in East Asia, with variations up to 25%. (2) The variation in seasonality is stronger in Northern America, whereas the variation related to day-to-day changing factors is stronger in East Asia. (3) Generalized linear models are built to capture the relationship between daily NTL and influential factors in each grid, revealing that approximately 25%∼50% of the daily variations can be explained by environmental factors, observational factors, and seasonality. (4) Environmental factors and observational conditions show spatially varying impacts on NTL. Specifically, aerosol exhibit opposite impacts on rural and urban areas; significant impacts of moonlight are mainly distributed in rural areas; the impact of satellite viewing angle is less pronounced and frequent in East Asian cities compared to those in North America. This research revealed the essential knowledge about variations of satellite-derived NTL and will benefit the processing and utilization of daily NTL products.