Long-Term Analyses of Aerosol Optical Thickness Using Caliop Masahiro Fujikawa, Rei Kudo, Tomoaki Nishizawa, Eiji Oikawa, Akiko Higurashi and Hajime Okamoto EPJ Web Conf., 237 (2020) 02023 Published online: 07 July 2020 DOI: 10.1051/epjconf/202023702023