LASER BEAM ATTENUATION IN THE LOWER ATMOSPHERE
BEGE (J R M) CO ARLINGTON MA
Pagination or Media Count:
Small angle spreading, aerosol scattering and molecular absorption are considered the important mechanisms for the weakening of a laser beam in the open atmosphere. Three different transmission laws are worked out for these three mechanisms. Both the physical principles and the numerical values encountered in the lower atmosphere are discussed and illustrated. Random density fluctuations in the turbulent atmosphere are discussed as the cause of small angular deflections in a narrow pencil of light. Beam attenuation due to atmospheric aerosol scattering is treated for an aerosol size distribution described by the sum of two inverse powers of the droplet radius. Laser beams can help find the parameters of such distributions. Molecular absorption is examined in terms of the narrow infrared lines of water vapour. An effort is made to present this difficult topic in as simple and useful a form as is compatible with the observational material. The formulae are designed to make it possible to estimate in detail how the atmosphere would weaken a laser beam under a wide variety of conditions. It is found that some effects are serious even at short ranges of a few meters, while in favourable circumstances, laser signals would not be drastically attenuated out to any practical distance in the lower atmosphere.
- Lasers and Masers
- Atmospheric Physics