SDGSAT-1 (Sustainable Development Science Satellite-1) is the world's first scientific satellite specifically designed to support the United Nations 2030 Agenda for Sustainable Development Goals (SDGs). Developed by the Chinese Academy of Sciences (CAS) and operated by the International Research Center of Big Data for Sustainable Development Goals (CBAS), it was launched on November 2021 into a sun-synchronous orbit at an altitude of approximately 505 km.
The satellite carries three complementary sensors: a Thermal Infrared Spectrometer (TIS), a daytime Multispectral Imager (MII), and a Glimmer Imager (GLI), a low-light imaging instrument capable of detecting night-time lights.
The spatial resolution the SDGSAT-1 GLI data is 10 m for the panchromatic band, and 40 m for the three multispectral bands (red, blue and green). The swath width is 300 km. The temporal revisit is around 11 days. The acquisition time is between 8 PM and 9 PM UTC.
Data are available on the SDGSAT-1 portal. Data are free of charge but restricted to scientific research. Thus, it is mandatory to submit a project on the portal, and for it to be accepted before accessing to some credits for downloading archives and programming acquisitions.
For Europe, a specific Google Earth Engine visualisation portal was created by the Universidad Complutense de Madrid, the University of Exeter, Plan-B and the CBAS.
The technical description of the sensor and the method for data calibration are provided in the SDGSAT-1 Data Users Handbook.
The panchromatic band contains three channels: Panchromatic Low (PL), Panchromatic High (PH) and High Dynamic Range (HDR), where the HDR is the 50% weighted average of PL and PH data.
The absolute calibration coefficients (Gain and Bias) of the GLI sensor are continuously updated and provided in the metadata of each product. Each band can be calibrated as follow: L=DN×Gain+Bias where L is the apparent radiance (W/m2/sr/μm), DN is the digital number of the band after relative radiometric calibration, and Gain and Bias are the calibration coefficients.
SDGSAT-1 data remain pioneering as they are the only high resolution nighttime images available for now. Nevertheless, some limitations must be pointed out:
Cloud coverage is difficult to detect on nighttime images (see dedicated section). Nevertheless, SDGSAT-1 satellite is also equiped with a thermal infrared sensor (TIS), which acquires images simultaneously with the GLI sensor. Clouds are generally well visible on thermal images, as they appear colder than the Earth background. Hence, the concomitant use of GLI and TIS images enables to detect clouds and to mask them on GLI data.