Radiation propagation in the atmosphere

When designing an optronic system whose sensor is located far from the source, one of the most important parameters is the spectral transmission of the atmospheric propagation medium. This is mainly affected by the absorption and scattering of radiation by this medium, the main sources of interaction between light and matter.

The performance of any optronic system is determined not only by its intrinsic technical characteristics resulting from its design and the technology used, but also by its behavior in the operational environment in which it is used. Thus :

• At the design stage or during development, it is important to know how these sensors will behave in a given climatic or meteorological situation;

• to use, it is useful to know how the nominal characteristics of these sensors vary according to the environmental conditions present.

The aim of this article is to show how the effects of the atmosphere affect the performance of optronic sensors.

The atmospheric environment, whether natural or loaded with artificial obscuring agents, affects the performance of optronic equipment in all spectral ranges (UV, visible, IR) and for laser radiation:

• by selectively attenuating radiation propagating towards the sensor at any wavelength;

• by generating an optical signal, comparable to noise, through diffusion or radiative emission, which weakens perceptual contrasts, the greater the distance.