TABLE OF CONTENTS Free-Space Optical (FSO) links involve the transmission, absorption and scattering of light by the Earth's atmosphere. The atmosphere interacts with light due to the composition of the atmosphere which, under normal conditions, consists of a variety of different molecules and small suspended particles called aerosols.
This interaction produces a wide variety of optical phenomena:
selective attenuation of radiation that propagates in the atmosphere,
absorption at specific optical wavelengths due to the molecules,
generation by scattering (the sky blue color, the red sunset, etc.) or by radiative emission of an optical beam comparable to noise at the source of perception contrasts loss. This loss is all the more important since the distance is large,
scintillation due to the variation of the air's refractive index under the effect of temperature (stars twinkle).
The construction of an optronic system, made up of a transmitter and a receiver in free atmosphere, requires a good knowledge of specific optical properties of the atmosphere like, for example, the spectral transmission of the propagation medium which is affected mainly by the scattering and the absorption of the radiation by this medium. In fact, the performance of any optronic system depends not only on its intrinsic design features resulting from its design and the technology used, but also on its behavior in its operational environment. Thus it is useful to know how optronic systems behave in differing climatic and weather conditions and particularly under prevailing environmental conditions.
To present the effects of...
