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Effect of dense atmospheric environment on the performance of laser radar sensors used for collision avoidance

The operation of laser radar in an automotive collision avoidance system under poor visibility conditions is analyzed. The equations were formulated to calculate (1) the signals returned to a laser radar system by a reflecting target positioned at a given range and (2) signals caused by the scattering of laser radiation by atmospheric particles only. The dependence of calculated signals on the density and the scattering properties of the atmospheric medium on one hand and on the geometry of the system on the other hand was studied. The multiple scattering processes were included in these calculations, and the polarization properties of the calculated signals were analyzed. An experimental verification of the theoretical results in a clear atmosphere and in a dense atmospheric environment has been performed. Good agreement was achieved only when multiple scattering was included in the theory. It is shown that multiple scattering is the main contributor to the signals received from the medium. Utilization of the results of this work can reduce significantly the very high false alarm rate typical for dense atmospheric conditions where successful anti- collision system performance is most crucial.