EULE -European Urban Light Explorer

The presentation will detail the proposed EULE mission -European Urban Light Explorer. It was originally proposed as Earth Explorer 12 to ESA (European Space Agency). At any moment, one half of the Earth's surface is experiencing daytime, and the other half nighttime. Most Earth surface observation missions focus on the first half. The EULE mission focuses on Earth's night. The scientific goal of EULE is to improve the understanding and quantitative description of artificial light during Earth's night. In achieving this goal, it provides a unique data stream for scientific questions related to anthropogenic and atmospheric light emissions. Artificial lighting of the night environment has brought enormous benefits to humankind, and has shaped societies in dramatic ways by enabling activities to take place despite a lack of natural light. The connection between human activity and light emissions means that artificial light is closely linked to social factors (e.g. wealth) as well as to environmental disruption (e.g. via light pollution). Recently 41 pressing scientific questions in seven thematic fields were identified that would benefit from improved nighttime visible band imagery. Research based on artificial nighttime light has increased rapidly in recent years, due to the introduction of improved instruments from the US and China. However, this research remains limited by the overall lack of current sensors, as well as issues related to their insufficient spatial resolution, spectral information, radiometric sensitivity, and revisits. Further issues are an overall lack of reliability, and overpass times which are not matched to peak evening emissions and with no detection of changes between evening and night activities. Compared to sunlight, artificial light sources are characterized by their spatial heterogeneity, as well as extreme variability in spectra, angular emission characteristics, and temporal properties. These factors interact to make interpretation of nighttime light series challenging. Consider, for example, that different sources are observed for the same area on Earth's surface, depending on whether the satellite view is from the East or West. This gives rise to considerable variability in observations from night to night, which causes problematic dispersion in the radiance values reported in monthly and annual composite images. Furthermore, the changing phase of the moon means that with a revisit cycle of 14 days or longer, geometric revisits often alternate between moon-lit and moon-free conditions. Changes in lighting technology have proved especially problematic for existing time series, as transitions from high pressure sodium to LED streetlights that preserve photometric illuminance can cause dramatic decreases in the radiance observed in a panchromatic band. The EULE mission would considerably advance the state of the art for most of the existing limitations of night lights data as a standalone satellite, and the overpass time limitation in synergy with other missions. It provides reliable radiometric observations in multiple spectral bands. This allows nighttime radiance to be re-expressed in terms of sensitivity curves, such as those for human or other animal vision systems, as well as the identification of lighting technologies. It has unprecedented sensitivity, making the detection of even individual spatially isolated artificial lights possible, and allows direct observation of the flux of artificial [...]