The horizontal variability of atmospheric backscatter may have a substantial effect on how Differential Absorption Lidar (DIAL) data must be taken and analyzed. To minimize errors, lidar pulse pairs are taken with time separations which are short compared to the time scales associated with variations in atmospheric backscatter. To assess the atmospheric variability for time scales which are long compared to the lidar pulse repetition rate, the variance of the lidar return signal in a given channel can be computed. The variances of the on-line, off-line, and ration of the on-line to off-line signals at given altitudes obtained with the dual solid-state Alexandrite laser system were calculated. These evaluations were made for both down-looking aircraft and up-looking ground-based lidar data. Data were taken with 200 microsecond separation between on-line and off-line laser pulses, 30 m altitude resolution, 5 Hz repetition rate, and the signal were normalized for outgoing laser energy
