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29 October 2007 Impact of turbulence on the measurement of CC&D materials in desert area
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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, Cn2, 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 arid 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 Cn2 values are representative for the diurnal run of Cn2 in arid 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 time of day and path length. Resulting MTFAs and the corresponding turbulence degradation factors will be discussed in details.
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Karin R. Weiss-Wrana and Alain Malaplate "Impact of turbulence on the measurement of CC&D materials in desert area", Proc. SPIE 6747, Optics in Atmospheric Propagation and Adaptive Systems X, 67470D (29 October 2007);


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