The monitoring of atmospheric conditions is very important for fluorescence observations. Particularly, the presence of clouds can drastically distort the signal from the extensive air shower. Infra-red (IR) sensors, measuring sky temperature, can help to distinguish clouds, which are usually significantly warmer than clear skies. An array of such sensors, covering the HiRes detector's field of view, was installed, and has been collecting data every minute of detector operation. Using this information, a cloud database was created. This database is used to select cloud free CR events. In this paper we present a description of the array and the method to analyze IR data.

High Resolution Fly's Eye (HiRes)

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 5 (HE part 2), pages 1153-1156