Effects of atmospheric scattering and extinction on the retrieval of fluorescence and Cherenkov signals produced by extreme energy cosmic rays and neutrinos from space: role of lidar for their assessment and correction

The impact of extreme energy cosmic rays on the Earthʹs atmosphere is manifested by the generation of fluorescence and Cherenkov radiation: these effects constitute source fields that propagate and, once detected, provide an indirect way to deduce energy, trajectory, composition of the primary particle. Because of the relatively infrequent probability of detection of such effects at the ground, proposals have been advanced to observe them from space: one of the proposed experiments is EUSO (Extreme Universe Space Observatory). Both the generation and propagation of these fields are affected by the high variability of the atmospheric conditions: to limit the deriving uncertainties, the observations would greatly benefit by the support of adequate instrumentation to provide the status of the atmosphere at the time of detection. Thus the use of an optical radar––lidar––has been suggested to complement the EUSO capability. This paper discusses: (a) the distortion induced by different atmospheric conditions on the fluorescence and Cherenkov profiles acquired from space; (b) the lidar retrieval of the transmission and scattering characteristics of the atmosphere and the use of these data to correct the detected signals to reach a realistic assessment of the atmospheric sources and of the primary particle characteristics. The simulations are based on experimental results with regard to aerosol and cloud backscatter data, on a relatively simple transfer model and on realistic assumptions regarding the extinction to backscatter ratio.