EUMETSAT Conference: M. Heumesser, O. Chanrion, T. Neubert, K. Dimitriadou, H. Christian, R. Blakeslee, N. Østgaard, A. Mezentsev and V. Reglero, Optical Signatures Associated with Terrestrial Gamma-Ray Flashes in the 777.4 nm band and their relevance for MTG-I LI, Wurzburg, Germany, 28 September- 2 October, 2020