THE EXTRACTION OF URBANIZED AREAS THROUGH IMAGES OF HIGH RESOLUTION NIGHTTIME LIGHTS

Abstract. Satellite nocturnal images of the earth are a useful way to identify urbanisation. Nighttime lights have been used in a variety of scientific contributions, including studies on the identification of metropolitan areas as well as landscapes impacted by urbanization. However, the study 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 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 study cases are Barcelona Metropolitan Region (Spain) and Shenzhen City (China).