Misalignment Effects on Lidar Backscatter Signals

Abstract

   The optical alignment of the axes of the laser transmitter and the receiving telescope is one of the fundamental problems in lidar systems. The receiver field of view is generally reduced to limit the sky background radiation. When the receiver's field of view is comparable to the divergence of the laser transmitter, accurate optical alignment is demanded. For checking the optical alignment, lidar backscatter signals at five wavelengths of ruby and YAG laser are calculated using a standard atmospheric model including the background stratospheric aerosols and mid-latitude ozone profile.
   Misalignment effects of the transmitter and receiver axes on the lidar signals and backscatter ratios of the stratospheric aerosols are investigated. When the transmitter and receiver axes are directed outward from a perfect optical alignment, the apparent backscatter ratio, R′_B, increases downward in an altitude range of 10-30 km even if there are no stratospheric aerosols. If the transmitter and receiver axes intersect each other, R′_B increases upward. A convenient method for the correction of R′_B is shown. It goes without saying that it is important to design the lidar system so that such misalignment will not occur.