Atmospheric horizontal uniformity measured by a steerable laser system at the high resolution fly's eye

The optical horizontal uniformity of the atmosphere surrounding the HiRes cosmic ray detector is measured using a steerable laser system (HR2SLS). Most models assume horizontal uniformity to achieve a one dimensional characterization of the atmosphere. The validity of this assumption is discussed. Possible asymmetries in the HiRes detector and HR2SLS are discussed. A method is developed whereby one can identify asymmetries in the atmosphere without being certain of the absolute calibration of the HiRes detector. At small scales, the atmosphere appears to be uniform but begins to show asymmetries at large distances.