Dalin, P., Connors, M., Schofield, I., Shelton, I., Zalcik, M., Pertsev, N., Sukhodoev, V., Perminov, V., McEwan, T., McEachran, I., Frandsen, S., Hansen, O., Andersen, H., Zadorozhny, A., & Romejko, V. (2007). Studies of noctilucent clouds with an inter-continental network of automatic digital cameras.