Radiometric Calibration of SDGSAT-1 Nighttime Light Payload

Nighttime light plays an important role in social economy and human activities by observing artificial light at night. Accurate radiometric calibration is the basis of quantitative applications and influences the accuracy of surface information revision. A nighttime light payload, named glimmer imager (GLI), is onboard the sustainable development goals satellite (SDGSAT-1). The payload can acquire nighttime light observations with a spatial resolution of 10 m in the panchromatic bands and 40 m in the red/green/blue (RGB) bands. In this article, we proposed a vicarious radiometric calibration method for the GLI of SDGSAT-1 based on point light source and conducted experiment in the Dunhuang radiometric calibration site. Atmospheric profile, aerosol optical depth (AOD), and total column water vapor content were measured during the in situ measurements and were used to simulate the at-sensor radiance at the entrance of satellite payload via moderate resolution atmospheric transmission (MOTRAN). Our result shows that there is a strong linear correlation between the simulated at-sensor radiance and the DN value, with R2 larger than 0.91. Moreover, uncertainties of the vicarious radiometric calibration induced by relative spectral response shift, AOD content measurements, atmospheric profile measurements, AOD-type assumption, and specialized point light itself are also discussed. Results show that the overall uncertainty of vicarious radiometric calibration for nighttime light payload onboard SDGSAT-1 based on point light sources is between 4.00% and 5.50%. The comparison between GLI/SDGSAT-1 and DNB/VIIRS at Athens, Denver, and Milan shows a strong correlation with R2 larger than 0.80. Our analysis reveals the feasibility of vicarious radiometric calibration method based on point light source for nighttime light payload.