Influence of atmospheric turbulence on imaging quality of electro-optical sensors in different climates
During long-term experiments FGAN-FOM measured Cn2 values over land with identical scintillometers in two different climates, in moderate climate in mid-Europe and in arid climate. Since Cn2 usually changes as a function of time-of-day and of season its influence on electro-optical systems can only be expressed in a statistical way. The cumulative frequencies of occurrence were calculated for a time period of one month for different times of the day. The statistical analysis was applied to calculate the effects of atmospheric turbulence on sensor performance like turbulence MTF, the resolution limit due to turbulence and intensity fluctuation. The calculations were performed for a SWIR sensor (active imaging system) and for typical MWIR and LWIR warning sensors. Turbulence MTF were calculated for a slant path of 5 km from the ground to a height of 100 m for upward and downward looking cases. For horizontal paths at a height of 2 m and 30 m the resolution limits due to turbulence were compared with the corresponding diffraction-limited ones. Calculations of the normalized intensity fluctuations were carried out for two slant propagation paths (zenith angle ? = 30° and 80°).