Effects of atmospheric obscurants on the propagation of optical/IR radiation

The magnitude and importance of the effect which various natural pollutants can have on the transmission of radiation at different wavelengths are examined. An example is presented for a 10 km long slant path from 1 km altitude to the surface with a mid-latitude winter atmosphere containing either a rural, urban, or maritime aerosol, a 100 meter thick layer of fog at the surface, and rain at two different rainfall rates. The transmittance over this 10 km slant path due to these atmospheric obscurants is obtained for the wavelength regions around 1, 4, and 10 microns, and for millimeter wave frequencies from 0-900 GHz using the FASCODE Program of the US Air Force Geophysics Laboratory. It is determined that natural atmospheric obscurants such as haze, fog, rain, or snow can significantly impede the performance of laser remote sensing systems, depending on laser wavelength, atmospheric conditions, and path length. The existing models are found to provide generally reliable estimates of these effects, although problems such as multiple scattering, propagation through snow, and correlation between optical effects and weather variability are not fully clarified.