In optical directional radio
, there are effects that interfere with the transmission, if it is over a long distance. Laser beams used for optical message transmission between a LEO satellite and a ground station pass through the atmosphere, which consists of air cells of different sizes that refract the laser beam differently at different temperatures. Thus, the atmosphere has a random refractive index in space and time, which is called refractive index turbulence (BIT). The laser beam is slightly deflected by the refractive index turbulence and additional intensity fluctuations occur due to interference effects. The described effect can be seen, for example, in the flickering of stars.