Effect of atmospheric extinction on laser rangefinder performance at 1.54 and 0.6 microns

Extinction of laser rangefinder (LRF) pulses by the atmosphere depends on the wavelength, weather conditions, and aerosol concentration along the optical path. In the IR, extinction is due to absorption by molecular constituents and scattering and absorption by aerosols. The total atmospheric extinction alpha(lambda) is the sum of the molecular and aerosol contributions, alpha(sub m)(lambda)and Alpha(sub a)(lambda). We present simple expressions for alpha(sub m)(lambda) and alpha(sub a)(lambda) for two LRF sources: Er:glass and CO2 which operate at 1.54 and 10.6 microns, respectively. The expressions are based on accepted models of atmospheric aerosols and molecular extinction and give an estimate of alpha(lambda) as a function of standard meteorological parameters, assuming horizontal beam propagation. Signal-to-noise ratios of LRF returns, measured from a reference target under different weather conditions are compared to predictions based on the estimate of alpha(lambda).