Version 2 of Hourly Aerosol Optical Centroid Height (AOCH) Data Product from EPIC/DSCOVR in Deep Space

Orbiting at Sun-Earth Lagrange-1 point, the Earth Polychromatic Imaging Camera (EPIC) provides sunlit Earth images at 10 channels from ultraviolet (UV) to near-infrared (NIR) every 1–2 h. Here, we presented the version 2 of the algorithm to retrieve aerosol optical depth (AOD) and aerosol optical centroid height (AOCH) from visible (443 and 680 nm) and O2 absorption (688 and 764 nm) bands of EPIC (hereafter AOCH-v2 algorithm). The EPIC AOCH-v2 algorithm differs from the version 1 (AOCH-v1) algorithm in several aspects. First, an independent calculation of ultraviolet aerosol index (UVAI) was added by using two UV bands (340 and 388 nm) to identify absorbing aerosols for AOCH retrieval. Second, we updated the real part of aerosol refractive index to represent a new smoke aerosol model for large smoke AOD scenarios over North America, while retaining the original smoke model generated from the Aerosol Robotic Network (AERONET) climatology for background aerosol cases. Third, a new AOD retrieval scheme was developed to constrain the surface reflectance using the climatological surface reflectance ratios. Finally, the cloud mask scheme was improved for cloud screening over bright surfaces. The EPIC AOD from the AOCH-v2 algorithm displays a better agreement with AERONET than AOCH-v1 algorithm. The evaluations against Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) measurements indicate that the AOCH overestimation in AOCH-v1 algorithm is significantly mitigated by AOCH-v2 algorithm, suggesting uncertainties in the EPIC AOCH retrievals are notably reduced through a better characterization of surface reflectance, enhanced AOD retrievals, and an updated smoke aerosol model.