Delimitation of urban systems by Luojia 1-01 nighttime light imagery

Satellite nocturnal images of the earth are a useful way to identify urbanisation. Nighttime lights have been used in a range of scientific contributions, including studies on building human development indices and on the identification of megalopolises and impacted landscapes. However, the study of the area and internal structure of urban systems by nighttime light imagery has had a fundamental limitation to date: the low spatial resolution of satellite sensors. Although the DMSP Operational Linescan System (OLS) has been gathering global low-light imaging data for over 40 years, its 2.7 km/pixel footprint has limited its use for in-depth studies of urban development. The 2011 launch by NASA and the NOAA of the Suomi National Polar Partnership (SNPP) satellite, with the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on board, has led to a significant improvement. This instrument has better spatial resolution (742 m/pixel), on-board calibration, a greater radiometric range, and fewer saturation and blooming problems than DMSP-OLS data. However, it still has considerable limitations for the in-depth study of the area and internal structure of urban systems. The launch of Luojia 1-01 in June 2018 has increased expectations. LJ1-01 is a nano satellite weighing 20 kg that can obtain high-resolution nocturnal images (130 metres/pixel). The aim of this paper is to analyse, and compare with previous satellites, the new instrument's capacity to delimit the urbanised area and its efficiency in identifying types of urban landscape (compact, dispersed and rurban). The case study is Barcelona Metropolitan Region (3,200 km(2), 4.7 million inhabitants).