干旱区生态环境知识资源中心

Within the scope of the investigation of material for camouflage, concealment, and deception (CC&D material) in desert environment, it is necessary to evaluate the impact of turbulence on thermal imagers in the MWIR and in the LWIR. Turbulence decreases the effectiveness of electro-optical systems. It causes a reduction of the spatial resolution of thermal imagers, which is characterized by the turbulence modulation transfer function MTF. Turbulence MTF depends on atmospheric parameters, e.g. the strength of atmospheric turbulence as described by the structure parameter of the refractive index fluctuations, C-n(2), the atmospheric path length, the cross-wind velocity, and on the sensor parameters, i.e. the wavelength and the aperture diameter of the front optics. The total MTF is the product of turbulence MTF and sensor MTF, which in turn is the product of detector MTF and optics MTF. As a figure of merit for the spatial resolution, we used the area under the total MTF (MTFA). Based on our turbulence measurement that was taken in and climate in Negev desert, Middle East, we calculated the total MTFA for a dual-band thermal imager (MWIR and LWIR) with two available optics under diverse turbulence conditions and for different path lengths up to 5 km. The selected C-n(2) values are representative for the diurnal run of C-n(2) in and summer or different times of day, respectively. We defined a turbulence degradation factor X to estimate the impact of turbulence on the image quality as a function of V time of day and path length. Resulting MTFAs and the corresponding turbulence degradation factors will be discussed in details.