Evaluating VIIRS EPS Aerosol Optical Depth in China: An intercomparison against ground-based measurements and MODIS

Abstract

The Visible Infrared Imaging Radiometer Suite (VIIRS) has been providing routine retrievals of aerosol properties since 2011. As a new generation advanced sensor, VIIRS has certain advantages in terms of spectral and accuracy and spatial resolution, especially with updated algorithm for the NOAA Enterprise Processing System (EPS) since July 2017. However, the VIIRS EPS aerosol products have not been extensively validated. In this study, we evaluate the VIIRS EPS AOD product over mainland China, which has been suffering from heavy aerosol pollution in the recent decade. By comparing collocated VIIRS and ground observations over 12 sites for the Aerosol Robotic Network (AERONET) and 5 sites from the Sun-sky radiometer Observation NETwork (SONET), we find that VIIRS AOD achieves overall reasonable agreement, with 50.61% falling within the expected accuracy interval and a correlation of 0.91 with ground observation. A positive bias of 0.13 is noticed with relatively larger mean bias found in the spring and summer. VIIRS AOD also has a high bias compared with MODIS. The bias is found to be slightly increasing with AOD level. The seasonal variability of VIIRS AOD are also mostly consistent with surface observation and MODIS. VIIRS aerosol model still needs improvement, especially for dust and urban aerosols. A Combined Principal Component Analysis (CPCA) to extract dominant spatial and temporal variability between VIIRS and MODIS data also shows very good agreement, an indication that VIIRS is capable of capturing the major aerosol variability over China.