In this report, the equations which describe the attenuation of long-wavelength electromagnetic radiation by water fogs and rain are briefly reviewed and explained under the assumption that the aerosol droplets are spherical and that the irradiance of the beam is in the "linear" regime. Calculations of water fog attenuation coefficients are made using the Rayleigh approximation, and an approximate error analysis of this approximation is made by comparing Rayleigh approximation calculations of absorption efficiency with exact Mie theory calculations of extinction efficiency. Numerical integration of the Mie extinction efficiency is used to compute the attenuation coefficient for rain with a Marshall-Palmer drop size distribution for various rain rates and temperatures. These results are compared with those given by a power law relationship with coefficients given by Olsen, Rogers, and Hodge which was used in the Near Milimeter Wave (NMMW) Module of the Electro- Optical Systems Atmospheric Effects Library (EOSAEL).

Unclassified report. ARL-TR-527.