Evaluation and Application of On-Orbit Calibration of the Automated Vicarious Calibration System

Observation sites using standard automated observation equipment and unified processing technology, such as the radiometric calibration network (RadCalNet) and the automated vicarious calibration system (AVCS) for continuous automated observation and independent on- orbit calibration and monitoring, are used to overcome difficulties of traditional vicarious calibration. In this article, the top-of-atmosphere (TOA) reflectance measured by five kinds of satellite sensors was used to evaluate the reliability of the AVCS-predicted TOA reflectance. The bidirectional reflectance distribution function (BRDF) model was introduced for observational geometric correction to meet the calibration requirements of sensors with different view angles. The mean relative deviation of the TOA reflectance between the predicted value and the sensor observations was within 3.5% (4.9% in the 661.4-nm band of Enhanced Thematic Mapper Plus (ETM+) and 6.9% in the SWIR2 band). Due to the less radiation performance evaluation of Fengyun-3D (FY-3D) Medium Resolution Spectral Imager-II (MERSI-II) in continuous time series, AVCS was used to perform continuous on- orbit calibration application of FY-3D MERSI-II in continuous time series. The results showed that each band had varying degrees of variation, among which the shortwave variation was more than 29%. An update of the calibration coefficient was needed. The consistency of TOA reflectance measured via Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and FY-3D MERSI-II after using the gain model was improved to varying degrees compared with the official gain. In the future, AVCS will be applied to the on- orbit calibration and radiation performance evaluation of various sensors, and improvement in the accuracy of the AVCS-predicted TOA reflectance for the band sensitive to water vapor is needed.