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| A night calibration of air opacity based on measurements carried out by a computer controlled digital photocamera: it is possible to study the nighttime variability of atmospheric transparency, due to clouds and aerosols, through the observation of starlight in the visible region. The large field of view of the optics permit to observe a large number of stars and, through an appropriate methodology, retrieve the optical thickness in direction of each star. Through the composition of some photo shots on the whole zenithal arc it is possible to obtain a map of optical thickness and of skylight background; a succession of these maps may provide the time variation of the aerosols presence. The camera can be used simultaneously to a LIDAR system to obtain the nighttime extinction-backscatter ratio or used as a detector for a LIDAR bistatic system. |